FAQs

What is RadarScope?

RadarScope is a specialized display utility for weather enthusiasts and meteorologists that allows mobile, Mac, and tablet users to view NEXRAD radar data and severe weather warnings. This premium application can display the latest reflectivity, velocity, and other radar products from any NEXRAD radar site in the United States, Canada, Guam and Puerto Rico. RadarScope is available on the App Store, Mac App Store and Google Play.

Who is it for?

RadarScope is for weather enthusiasts, meteorologists, or anyone who has an interest in weather radar. We come from Tornado Alley, and RadarScope at its roots comes from a meteorological background. That’s not to say it’s only for meteorologists (it’s not), but it’s not necessarily the same thing you see on your evening news (except maybe if you live in Tornado Alley). Showing an image of where precipitation is falling is sufficient for most people, and there are no shortage of websites that can give you that information, and even other native iPhone apps do a great job of showing radar mosaics. RadarScope is designed to do more than that, for those that need more detail, more flexibility, and more than just precipitation. For example, most people probably have no need to look at Doppler velocity data, but for those that do, they understand that it’s not the type of thing you’ve been able to do on a mobile platform like this before.

Can I get lightning data in RadarScope?

For those who upgrade to the Pro version of RadarScope, lightning data becomes available, in addition to 20 previous frames of data on the WDT data feed. Here’s info about lightning in RadarScope:

  • Lightning updates every minute
  • Lightning is non-gridded offering the best depiction on the map regarding strike location
  • Lighting strikes fade upon the 30-minute mark to indicate new vs. old strikes
  • Lightning animates with the radar

 

2015-04-25 20.14.11

RadarScope’s AllisonHouse integration also supports the display of lightning using your AllisonHouse subscription.

What happened to SuperRes data?

SuperRes data are only available using the WDT and RadarScope Pro data feeds. If you suddenly find yourself without access to SuperRes products, your data source is likely set to another source. This setting is found in RadarScope Settings > Settings > Radar Data

Why does it say “Not Available”?

There are times when a radar is down for a significant amount of time causing the last file sent from the radar to age off of our servers. In this case, the app is not able to download your selected product.

NotAvailableWeb

What is SAILS mode?

When RadarScope 2.2 was launched, it included support for rapid updates in SAILS mode. In this blog, we will explain what SAILS mode is.

SAILS stands for Supplemental Adaptive Intra-Volume Low-Level Scans. The concept adds a low level scan during the modes of operation used in the modes used for severe weather observations. This new low level scan is introduced into the approximate middle of the volume scan. In a volume scan, the radar scans elevation angles between .5° and 19.5°. When the radar has an AVSET termination angle of 19.5 degres and the current scan reaches 3.1°, the radar transitions back to the .5° elevation for an additional scan and then elevates back up to 4° to complete the volume scan. Lower AVSET termination angles results in a quicker insertion of the SAILS scan. This additional scan allows for more frequent scans of the lower levels and only increases the volume scan times to at most 40 seconds.

You can learn more about SAILS from the National Weather Service http://www.weather.gov/gsp/sails.

Does RadarScope collect information about me or my phone?

RadarScope accesses radar data via static URLs on web sites operated by NOAA’s National Weather Service and our commercial data providers. If you click the “Visit Web Site” button on the preferences panel, RadarScope will load a help page. RadarScope also contacts WDT web servers to obtain radar status reports.

If you are a member of the Spotter Network and you choose to report your location to the Spotter Network, RadarScope will send your location information to the spotternetwork.org web server every two minutes.

RadarScope collects statistics on how much radar data you download and reports the total number of bytes downloaded to our web server not more than once a day. We plan to use this information to determine total bandwidth usage by RadarScope and determine the overall impact on the servers from which RadarScope obtains its data. This information will help us plan for new products and services in future versions.

We respect your privacy as much as our own. We don’t collect any information about you, your phone, or how you use our software aside from that documented above. It’s conceivable that future versions might include features that require the collection of usage patterns or other information directly related to the use of the software. If we decide to offer such features in a future release, we will disclose it to you.

Hey, what’s the deal with all this ground clutter I’m seeing?

When there is no precipitation in the area, it’s very common for the radar to be operating in what is called “clear air mode”. When in this mode, the radar is operating more slowly so that it can be more sensitive and pick up weaker returns (and hence more clutter). But why would it do this? Why would you want to see this?

Clear air mode gives it the ability to see things like flocks of birds, insects and bats, but for meteorologists it provides the ability to see things like cold fronts and subtle airmass boundaries. When conditions are right, these boundaries can become the focus point for storm initiation, so being able to see them is extremely useful.

Clear air mode is also useful for detecting very light drizzle and light snow. Sometimes these phenomena do not generate a strong enough return signal to be detected in precip mode, but stick out like a sore thumb in clear air mode.

You can think of the two modes, clear air and precip mode, as opposite ends of the same scale, with clear air mode on the low end and precip mode on the high end.

To the uninitiated, clear air mode may just look like useless ground clutter, but in that data can lie very important hints about what the atmosphere is up to.

Here’s an example of a radar in clear air mode.

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Why doesn’t it update more frequently?

When a radar is in precipitation mode, the radar transmits updates usually every 5-8 minutes. In clear air mode, the updates are about every 10-12 minutes. When the data you’re looking at are fresh, RadarScope doesn’t bother checking the server again until it’s likely that an update is available. When the product you are viewing becomes more than five minutes old, RadarScope begins polling the server once a minute to check for a new product. It could check for data more often, but that would drain your battery more quickly.

What is different between RadarScope’s display and the images available on radar.weather.gov?

RadarScope uses the raw Level III data to generate an interactive display that you can zoom, scroll, etc. Since it uses Level III data, the display is in the true radial format of the radar, which is beneficial for its resolution and compact size. The images you see on the radar.weather.gov website are static and can’t be explored in the way you can in RadarScope. The data that RadarScope downloads from the NWS is surprisingly compact, which is great for those on the go.

Why does it say “Cannot contact server”?

RadarScope cannot establish a connection to data provider you’ve selected, therefore it cannot get data to display. Please see the disclaimers on the NWS website (http://www.weather.gov/disclaimer.php) and in our Terms of Use regarding data availability.

Why does it say “Image is X minutes old”?

When the data start to become stale, RadarScope will alert you to this fact with the above status message.

This can be for any number of reasons: Sometimes the radar is down for repair or maintenance, sometimes the server may be slow, etc.

If the radar does not update for an extended period, go to the application settings and tap the View Support Page button. Our iPhone-optimized support page includes radar status messages that indicate which radars are currently offline and may provide additional information about the problem. You can also check http://radar2pub.bldr.ncep.noaa.gov/ or http://www.weather.gov/view/validProds.php?prod=FTM for radar status. Those pages will give more details about what exactly is going on and when you might expect data to start flowing again.

Since RadarScope uses publicly available data feeds from NOAA and our commercial providers, and their servers are subject to slowdowns and heavy loads, unfortunately there can be no guarantees for data timeliness or availability. Please see the disclaimer on the NWS website (http://www.weather.gov/disclaimer.php) as well as our Terms of Use.

Where does the data come from?

The United States radar data originate from NOAA’s network of WSR-88D NEXRAD and FAA Terminal Doppler Radars and are in the public domain. RadarScope can obtain data from NOAA’s NWS data feed at weather.noaa.gov and commercial data feeds, so you have alternatives for getting data. Please refer to the NWS data disclaimer for more information. (http://www.weather.gov/disclaimer.php). Canadian radar data originate from Environment Canada’s network of weather radars across Canada.

Does it display animated loops?

Yes. RadarScope can download and animate over the latest six to twenty frames of data. Looping more the six frames of data with the WDT data provider requires a Pro subscription.

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Does it work for Puerto Rico, Hawaii, Alaska, or Guam?

Yes!

User’s Guide

Tools

How do I access the map tools?

On iPhone, you can access RadarScope Map Tools by tapping and holding on the map tools button located on the left side of the top toolbar.
iPhoneToolsMenu
On iPad, you can access RadarScope Map Tools by selecting the desired tool on the left side of the top toolbar.
iPadTools
On Android, you can access RadarScope Map Tools by and holding on the map tools button located on the right side of the bottom toolbar.
AndroidTools
On Mac, you can access RadarScope map tools on the right side of the unified toolbar.
Mac Map Tools

Changing Radars

Changing the selected radar can be done in two ways. One, chosing the Radar Selection Tool from the Map Tools menu and picking a radar on the map. Two, selecting a desired radar site from the radar list.

On iPhone, tap and hold the Map Tools icon located in the title bar and tap the Selection Tool. Now chose a radar from the map. Tap the Selection tool icon again to turn off Radar Selection Mode. To see a list of radars, tap the radar ID in the title bar and chose the Radar tab. A list of your favorite radars will be shown at the top while a list of all radars separeted by state is shown belows.

  • iPhone Change Radars Video

On iPad, tap the Selection Tool located on the left side of the title bar to toggle Radar Selection mode. To see a list of radars, tap the radar ID in the title bar and chose the Radar tab. A list of your favorite radars will be shown at the top while a list of all radars separeted by state is shown below.

  • iPad Change Radars Video


iPadChangeRadars

On Android, tap and hold the Map Tools icon located in the title bar and tap the Selection Tool. Now chose a radar from the map. Tap the Selection tool icon again to turn off Radar Selection Mode. To see a list of radars, tap the radar ID in the title bar and chose the Radar tap. A list of your favorite radars will be shown or you can tap View All Radars to show a list segmented by state.

  • Android Change Radars Video


AndroidChangeRadars

On Mac, click the Radar Selection Tool lacated in the center-left of the unified toolbar. To see a list of radars, select Radars from the inspector menu.
MacChangeRadars

Changing Products

The product menu displays a list of available radar products. Tap on the product tab at the bottom of the screen to reveal the menu.
Changing the selected radar can be done in two ways. One, choosing the Radar Selection Tool from the Map Tools menu and picking a radar on the map. Two, selecting a desired radar site from the radar list.

iPhoneChangeProducts
iPadChangeProducts
AndroidChangeProducts
macOSChangeProducts

Inspecting

With RadarScope Pro, you can inspect each radar data bin value with the Inspector Tool.

On iPhone, you can activate the Inspector Tool from the Map Tools menu located in the left side of the top toolbar.

  • iPhone Inspector Video

iPhone Inspector

On iPad, you can activate the Inspector Tool by tapping the Inspector icon located on the left side of the top toolbar.

  • iPad Inspector Video

iPad Inspector

On Android, you can activate the Inspector Tool from the Map Tools menu located on the right side of the bottom toolbar.

  • Android Inspector Video

Android Inspector

On Mac, you can activate the Inspector Tool by tapping the Inspector icon located on the right side of the unified toolbar.

  • Mac Inspector Video

Mac Inspector

Loop Scrubbing

Yes, RadarScope includes a loop scrubbing feature allowing you to manually step through previous radar frames. Just tap and hold on the play button to reveal the loop scrubber.

LoopScrubbing

Drawing

You can draw on the map by enabling the Drawing Tool from the Map Tools menu.

On iPhone, you can activate the Drawing Tool by tapping and holding on the Map Tools menu and selecting Draw.

  • iPhone Drawing Video

iPhone Drawing
iPhone Drawing

On iPad, you can activate the Drawing Tool by tapping the Draw icon located on the left side of the top toolbar.
iPad Drawing
iPadDrawing2
  • Android Drawing Video

AndroidDrawingTool

On Mac, you can activate the Drawing Tool by clicking the Draw icon located on the right side of the unified toolbar.
MacDrawing

Sharing

RadarScope allows you to share an image to your camera roll, Twitter, Facebook, and other sources. The image output using the share tool is configured specifically for sharing. If you tap the share button while looping, RadarScope will export a loop. You can export your loop as a gif, video, or directly to social media.


On iPhone, tap the share icon located on the toolbar.

  • iPhone Sharing Video

iPhoneShare

On iPad, tap the share icon located on the toolbar.
On Android, tap the share icon located on the toolbar.
AndroidShareTool
On Mac, tap the share icon located on the right side of the unified toolbar.
MacTools

Examples

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Measuring

RadarScope’s measuring tool allows you to measure a distance from one point to another. You can start and end the tool from any point on the map. If you start the measuring tool from the selected radar site, the tool also displays the pulse height. Note, pulse height is calculated using standard refraction.

On iPhone, you can activate the Distance Tool by tapping and holding the Map Tools menu located on the left side of the top toolbar and select Distance.

  • iPhone Measuring Video

iPhone Measuring

On iPad, you can activate the Distance Tool by tapping the Distance icon located on the left side of the top toolbar.

  • iPad Measuring Video

iPad Measuring

  • Android Measuring Video

AndroidMeasure1
AndroidMeasure2

On Mac, you can activate the Distance Tool by tapping the Distance icon located on the right side of the unified toolbar.
MacMeasuring

Settings

How to setup a second display

To AirPlay RadarScope, swipe up from the bottom of the screen to reveal the iOS Control Center. Now select your desired Apple TV and enable mirroring.

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Mirroring is also supported on certain Android devices using Chromecast. You will need to confirm your device is capable of Chromecast mirroring by visiting Google’s support website. https://support.google.com/chromecast/answer/6059461?hl=en

Storm Tracks

Storm tracks display the predicted path of the storm. Each tick on the path show the approximate time in 15 minute intervals along the path of the storm. Storm tracks are updated every two minutes.

Photo 2015-07-08, 15 43 51

Watches & Warnings

The following warnings are available in RadarScope:

  • Severe Thunderstorms
  • Tornadoes
  • Flash Floods

Warning polygons are displayed directly on the map. You can zoom out and pan around the map to view these warning polygons. When active warnings are in effect, a button will appear to the right of the radar name in the bar at the top of the map. Tap the badge, then tap “Warnings” to see the warning list. Tap on a specific warning in the list to view it on the map, or tap the disclosure button to the right of the warning description to read the full text.

Read Warnings

  1. Tap on the warning button to the right of the radar name
  2. Tap on “Warnings”
  3. Tap the disclosure button for a specific warning in the list

Show Warnings on Map from List

  1. Tap a warning in the list to display the map showing the warning polygon

Read Watches

Watches require AllisonHouse integration.

  1. Tap on the warning button to the right of radar name
  2. Tap on “Watches”
  3. Tap on the specific watch in the list

Find Watches on Map from List

  1. Tap on “View in Map” to display the map showing the warning polygon

Radar Data

RadarScope allows you to select from multiple radar data sources.

  • WDT – Weather Decision Technologies includes SuperRes and Canadian data.
  • RadarScope Pro – WDT Data with increased loops times and research radars.
  • AllisonHouse – Requires an AllisonHouse subscription. Does not include SuperRes, Canadian, or Reaserch data.
  • NOAA – Data from the National Oceanic and Atmospheric Administration feed. Does not include SuperRes, Canadian, or Reaserch data.

WeatherOps Account

RadarScope provides integration for customers of WeatherOps Commander. Once your are logged into your WeatherOps Commander account, you will be able to see your assets displayed on the RadarScope map. You can sign into your WeatherOps account under Settings. Once you are loggen in, you can toggle the display of your WeatherOps assets using the Assets Layer setting.

You can learn more about WeatherOps at their website: http://wdtinc.com/weatherops/

iPhoneWxOps
iPadWxOps
AndroidWxOps
On Mac, WeatherOps integration is currently not avalible.

Lightning Data

RadarScope allows you to select from two lightning data sources.

  • RadarScope Pro – Provides high-resolution cloud-to-ground lighting strikes within the radar domain. Strikes also animate while looping. Requires a Pro subscription.
  • AllisonHouse – Customizable in your AllisonHouse account settings to provide cloud-to-ground or all strikes. Data does not animate while looping. Requires an AllisonHouse subscription.

SpotterNetwork Account

The SpotterNetwork brings storm spotters, storm chasers, coordinators and public servants together in a seamless network of information. It provides accurate position data of spotters and chasers for coordination/reporting and provides ground truth to public servants engaged in the protection of life and property.

With RadarScope, you can view the lcoations of fellow spotters on the RadarScope map. You can also enable location reporting and RadarScope will keep your SpotterNetwork location upated while you’re using RadarScope.

iPhoneSpotterNetwork
iPadSpotterNetwork
AndroidSpotterNetwork
MacSpotterNetwork

Auto Radar Selection

When enabled, Auto Radar Selection will automatically pick the nearest, online radar when you activate your currect location or chose a saved location.

Screen Lock

When enabled, Screen Lock will prevent your device from sleeping.

Expert Mode

When enabled, Expert Mode will adjust the reflectivity color table to show all returns. By default, RadarScope does not show radar returns below 0 dBZ in an effort to reduce ground clutter. However, there are cases when seeing all returns is helpful such as front identification or non-meteorological returns like bats or smoke.

Show TDWRs

When enabled, you will be able to view data from Terminal Doppler Weather Radar sites in RadarScope. These radars are off by default because TDWRs require special considerations when interpreting their data. Please use caution when using TDWR data.

Use Metric Units

When enabled, RadarScope will use metric units for displaying data.

RadarScope Pro

What is this RadarScope Pro subscription all about?

RadarScope Pro is a $9.99 yearly subscription available via in-app purchase that provides access to the following:

  • Real-time non-gridded lightning data feed that animates with the radar – absolutely the most accurate and fastest lightning information available
  • Extended radar data feed for up to 20 frames of Level 2 “Super Res” data extending playback for a more complete dataset
  • Ability to use RadarScope on your WATCH
  • Inspector Tool

Data we are offering in the pro version is fairly expensive to purchase, then redistribute. We wanted to offer the data but could not under any other means than subscription as we incur a recurring yearly cost for each lightning license and increased bandwidth cost for both lightning and radar data redistribution. We intend to continue to create components for the Pro feature and do not foresee the need for additional costs.

I purchased RadarScope Pro in 2009 and it is asking me to buy again!

RadarScope Pro is a yearly subscription within the RadarScope app and was first introduced in 2014. The RadarScope app costs $9.99 in the App Store. Should you decide you want access to the Pro features, this is an additional $9.99 yearly subscription.

Why does it say my email is not recognized?

Due to differences in how Apple and Google Play handle subscriptions, iOS and Mac customers will need to register their subscription with us upon purchase. However, the registration step is optional. It is possible you skipped the registration step in your excitement to try out the new features!

No worries, there are a few things you can do

  • If you still have the device you purchased Pro on, head to RadarScope Settings > Pro > Register. You will now be prompted to enter your email for registration.
  • If you do not have the device you purchased Pro on, simply send a screenshot of your Pro purchase receipt to our 24/7/365 support team and they can enter your subscription for you. Support can be contacted by going to RadarScope Settings > Settings > Support > Email.

I have an iPhone, an Android tablet, and a Mac, can I use the same subscription on all devices?

Since each platform (iOS, Mac, and Android) use a different App Store, it is not possible to use the same subscription across platforms. In-app subscriptions are much like apps in that they cannot be transferred from one platform to another.

I just got the sweet new iPhone. How do I get Pro back?

Congratulations on your new purchase! You can restore your RadarScope Pro subscription by going to RadarScope Settings > Pro > Restore. You can now enter the email address you used to register Pro with. In a few minutes you will receive an email with a restore link. Just tap the link and Pro will be restore to your new iOS device!

I just got a new Android phone. How can I get Pro back?

Since Google Play manages your RadarScope Pro subscription, Pro will automatically restore to your new device.

I got the restore email but I can’t tap the link!

RadarScope uses a special link to pass information to the RadarScope app. Some third-party mail apps (Gmail, Yahoo, etc) do not honor these special links. You can either open the email using the built-in mail app or copy and paste the “radarscope:///activate?xxxxxx” text into the Safari address bar.

Radar Products

SuperRes / Base Reflectivity

NEXRAD radars work by bouncing radio waves off particles in the air. Those particles could be raindrops, hail, snow, or even dust and insects. The amount of energy that bounces off of those particles and returns to the radar is called “reflectivity” and is represented by the variable “Z”. Reflectivity covers a wide range of signal strength, from very weak to very strong, so it is measured on a decibel (logarithmic) scale in units of dBZ, or decibels of Z. The higher the dBZ value, the larger the number and/or size of the particles the radar beam is seeing.

The dBZ values increase as the strength of the signal returned to the radar increases. The scale of dBZ values is related to the intensity of rainfall. It is important to remember, however, that the radar shows only areas of returned energy and not necessarily precipitation. So the presence of a return, especially a very weak return below 20 dBZ, doesn’t always mean that it’s raining.

The colors along the bottom of the map correspond to precipitation types and intensities. When you move your cursor across the squares, RadarScope will display a value for each color. NEXRAD radars can’t distinguish between different types of precipitation with absolute certainty. However, reflectivity values can be somewhat roughly associated with different precipitation types:

  • 10 dBZ (blue) – Very light rain or light snow
  • 20 dBZ (green) – Light rain or moderate to heavy snow
  • 30 dBZ (yellow) – Moderate rain or sleet showers
  • 40 dBZ (orange) – Moderate to heavy rain or sleet showers
  • 50 dBZ (red) – Heavy thunderstorms
  • 60 dBZ (pink) – Intense to severe thunderstorms with hail

Like in the movie “Pirates of the Caribbean,” these reflectivity values are more like guidelines than rules. This is a rough guide only. The atmosphere is a complex system, so you can’t always associate particular values with precise conditions or events. As a general rule, the higher the dBZ value, the heavier the concentration of objects at that location in the atmosphere.

10690276_10152798860868734_5782038195491342255_n 2014-05-11 16.48.12

10620792_10154499341430652_4701660860601774726_n 2014-08-27 19.41.07 10358913_10204589439006680_1935370937348053373_o 2014-08-27 18.40.36

You can learn more about base reflectivity products on this NWS web page:

SuperRes / Base Velocity

SuperRes and Base velocity indicates storm motion toward or away from the radar, measured in m/s. The velocity products in RadarScope use the Doppler effect to determine how fast the particles in the air are moving relative to the radar itself. Negative values (green in RadarScope) indicate motion toward the radar, while positive values (red in RadarScope) indicate motion away from the radar. They can be difficult to interpret without training and experience, but Doppler velocity products can be used to detect the overall movement of a storm as well as relative motion within the storm itself, such as rotation.

Note that the radar can only detect the component of the velocity vector along the radar beam, so this isn’t a full picture of the wind field. But it gives you a fairly good idea which way a storm is heading.

10671265_810160035672891_8435088547428156699_n 2014-05-11 17.43.32

10447725_10203580482727310_1043540543942986458_n  1969314_10204990623342608_2490934497997589713_n 10485962_735532513196397_1912700167631269045_o

10531252_10204589429686447_8850686890842152574_o 10548085_10204589423326288_2744710080334505457_o 10655208_366904196803480_3766568303991374424_o

Since the beam is sent out at an angle to the ground, it is looking higher up in the atmosphere as it gets farther from the radar. So the data you see in a radar image are often thousands of feet above the ground. At that height, wind speeds are often higher than they are on the ground. Doppler velocity products are valuable tools for meteorologists to use to determine motion in storm systems. But if you’re interested in surface level winds, your best bet is to look at data from weather stations on the ground. There are several other sources on the web which provide such information.

You can learn more about base velocity products on this National Weather Service page:

Precipitation Depiction

Precipitation Depiction is a proprietary WDT product combining SuperRes reflectivity data and surface observations to show a depiction of the current hydrometeor type.

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Echo Tops

The echo tops product shows the maximum height of precipitation echoes detected by the radar between 5,000 and 70,000 feet that exceed 18 dBZ. Higher echoes are often associated with stronger areas of a storm. This product is useful for identifying strong updrafts, and a sudden drop can indicate the onset of a downdraft. Some storms are too close to the radar for the beam to see the top, so echo tops is often underestimated for strong storms near the radar.

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HiRes Vertically Integrated Liquid

The vertically integrated liquid (VIL) product estimates the amount of water in a column of air. High values for VIL can indicate heavy rainfall or the presence of hail. When VIL values fall rapidly, it may indicate a downburst. VIL is subject to radar limitations and seasonal dependencies, so it’s a tricky product to interpret.

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Learn more about vertically integrated liquid from this Wikipedia web page:

Estimated Rainfall

The rainfall products are estimates of how much rain has fallen at a particular location. The National Weather Service has computers that analyze the reflectivity values returned by the radar and estimate how much rain has fallen. It is not, of course, perfectly accurate but it usually gives you a good idea of the relative amount of rainfall at various locations within the radar’s coverage area. The One Hour Surface Rainfall product provides an estimate of how much rain has reached the ground in the past hour. The Storm Total Surface Rainfall product does the same thing for an arbitrary period of time specified by the radar operator, usually corresponding to the beginning of a rainfall event. Since this product is based on the relationship of reflectivity (Z) to rainfall rate (R), it is important to note that it is not an indicator of snowfall accumulation.

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You can learn more about precipitation estimates on these National Weather Service pages:

Storm Relative Velocity

Storm relative velocity is simply base velocity with the average storm motion subtracted out. When storms are moving quickly, this makes it easier to spot green/red velocity couplets that are indicative of rotation and which might be masked out by the motion of the storm. As with base velocity, green is motion towards the radar and red indicates motion away.

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It’s also worth noting that the above rotation images are ideal cases. We aren’t always lucky enough to get such prominent radar signatures from tornadoes. The radar isn’t looking at ground level, so it can’t actually see the tornado itself. It’s seeing rotation higher up in the storm covering an area that is several miles wide. The height and width of the radar beam increases with its distance from the radar. So the farther away a storm is from the radar, the higher up the radar is seeing and the wider the beam, making it is less likely to detect the rotation associated with a tornado.

You can learn more about storm relative velocity on this National Weather Service page:

Classic Velocity

Base velocity indicates storm motion toward or away from the radar, measured in knots. One knot is equal to one nautical mile per hour, or about 1.15 miles per hour. The velocity products in RadarScope use the Doppler effect to determine how fast the particles in the air are moving relative to the radar itself. Negative values (green in RadarScope) indicate motion toward the radar, while positive values (red in RadarScope) indicate motion away from the radar. They can be difficult to interpret without training and experience, but Doppler velocity products can be used to detect the overall movement of a storm as well as relative motion within the storm itself, such as rotation.

Note that the radar can only detect the component of the velocity vector along the radar beam, so this isn’t a full picture of the wind field. But it gives you a fairly good idea which way a storm is heading.

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Since the beam is sent out at an angle to the ground, it is looking higher up in the atmosphere as it gets farther from the radar. So the data you see in a radar image are often thousands of feet above the ground. At that height, wind speeds are often higher than they are on the ground. Doppler velocity products are valuable tools for meteorologists to use to determine motion in storm systems. But if you’re interested in surface level winds, your best bet is to look at data from weather stations on the ground. There are several other sources on the web which provide such information.

You can learn more about base velocity products on this National Weather Service page:

Classic Reflectivity 248 mmi

The 248 nautical mile classic reflectivity product is an older product that shows the same data as the base reflectivity tilt 1 product, but with less spatial and color resolution. For most situations, we recommend the use of base reflectivity tilt 1 instead.

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Composite Reflectivity

Composite reflectivity combines data from all elevation scans, or tilts, to create a single product. The resulting image shows the highest reflectivity value from the vertical cross section at that location. Composite reflectivity can reveal important features in a storm’s structure that might not be seen in the base reflectivity product.

Because it combines data from all the tilts, the composite reflectivity product is one of the last to be produced during a volume scan. As with all NEXRAD products, it’s important to remember that the data displayed in the image depict conditions that have already happened rather than what is happening right now.

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Learn more about composite reflectivity from this National Weather Service web page:

Classic Reflectivity

NEXRAD radars work by bouncing radio waves off particles in the air. Those particles could be raindrops, hail, snow, or even dust and insects. The amount of energy that bounces off of those particles and returns to the radar is called “reflectivity” and is represented by the variable “Z”. Reflectivity covers a wide range of signal strength, from very weak to very strong, so it is measured on a decibel (logarithmic) scale in units of dBZ, or decibels of Z. The higher the dBZ value, the larger the number and/or size of the particles the radar beam is seeing.

The dBZ values increase as the strength of the signal returned to the radar increases. The scale of dBZ values is related to the intensity of rainfall. It is important to remember, however, that the radar shows only areas of returned energy and not necessarily precipitation. So the presence of a return, especially a very weak return below 20 dBZ, doesn’t always mean that it’s raining.

The colors along the bottom of the map correspond to precipitation types and intensities. When you move your cursor across the squares, RadarScope will display a value for each color. NEXRAD radars can’t distinguish between different types of precipitation with absolute certainty. However, reflectivity values can be somewhat roughly associated with different precipitation types:

  • 10 dBZ (green) – Very light rain or light snow
  • 20 dBZ (green) – Light rain or moderate to heavy snow
  • 30 dBZ (yellow) – Moderate rain or sleet showers
  • 40 dBZ (orange) – Moderate to heavy rain or sleet showers
  • 50 dBZ (red) – Heavy thunderstorms
  • 60 dBZ (pink) – Intense to severe thunderstorms with hail

Like in the movie “Pirates of the Caribbean,” these reflectivity values are more like guidelines than rules. This is a rough guide only. The atmosphere is a complex system, so you can’t always associate particular values with precise conditions or events. As a general rule, the higher the dBZ value, the heavier the concentration of objects at that location in the atmosphere.

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You can learn more about base reflectivity products on this NWS web page:

Hydrometeor Classification (HC)

Hydrometeor Classification (HC) is an algorithm to identify the predominant hydrometeor in the radar beam. The pre-defined categories recognized under this classification are as follows:

  • BI- Biological (birds, insects)
  • GC – Ground clutter (buildings, trees)
  • IC – Ice crystals
  • DS – Dry snow
  • WS – Wet snow
  • RA – Light/moderate rain
  • HR – Heavy rain
  • BD – Big drops
  • GR – Graupel (soft ice, snow pellets)
  • HA – Hail-rain
  • UK – Unknown
  • RF – Range folded

The Hydrometeor Classification product should be used in conjunction with other data for proper interpretation, as it is merely an algorithm and not an absolute indicator of what is occurring at a particular location. As currently implemented, the algorithm determines only the most likely type of hydrometeor, omitting information pertaining to the likelihood of other categories.

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Specific Differential Phase (KDP)

Differential phase shift in general (technically classified as propagation differential phase shift) is the difference between the horizontal and vertical pulses of the radar as they propagate through a medium such as rain or hail and are subsequently attenuated (slow down). Due to differing shapes and concentration, most targets do not cause equal phase shifting in the horizontal and vertical pulses. When the horizontal phase shift is greater than the vertical the differential phase shift is positive, otherwise it is negative. Stated differently, horizontally oriented targets will produce a positive differential phase shift, whereas vertically oriented targets product a negative differential phase shift.

While this correspondence between positive values (horizontal) and negative values (vertical) is analogous to Differential Reflectivity (ZDR), there is a key distinction: differential phase is dependent on particle concentration. That is, the more horizontally oriented targets are present within a pulse volume, the greater the positive differential phase shift. Thus a high concentration of small raindrops could yield a higher differential phase value than a smaller concentration of larger raindrops. Differential phase shifting is largely unaffected by the presence of hail, and shifts in snow and ice crystals are typically near zero degrees. Non-meteorological echoes (birds, insects, and so forth) produce highly variable differential phase shifts.

Specific Differential Phase (KDP) is defined as the range derivative of the differential phase shift along a radial. Its possible values range from -2 to 7 in units of degrees per kilometer. It is available in two resolutions: 8-bit at 1 degree x 0.25 km resolution and 4-bit at 1 degree x 1.0 km resolution. It is best used to detect heavy rain. Areas of heavy rain will typically have high KDP due to the size or concentration of the drops. Hail and snow/ice crystals have no preferential orientation and will yield KDP values near zero degrees. Non-meteorological echoes will result in noisy KDP values. KDP is not calculated for areas in which the Correlation Coefficient (CC) is less than 0.9, which will result in gaps in the rendered data.

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Correlation Coefficient (CC)

The Correlation Coefficient (CC) product is defined as the measure of how similarly the horizontally and vertically polarized pulses are behaving within a pulse volume. Its values range from 0 to 1 and are unitless, with higher values indicating similar behavior and lower values conveying dissimilar behavior. The CC will be high as long as the magnitude or angle of the radar’s horizontal and vertical pulses undergo similar change from pulse to pulse, otherwise it will be low. It is available in two resolutions: 8-bit at 1 degree x 0.25 km resolution and 4-bit at 1 degree x 1.0 km resolution.

Correlation Coefficient serves well at discerning echoes of meteorological significance. Non-meteorological echoes (such as birds, insects, and ground clutter) produce a complex scattering pattern which causes the horizontal and vertical pulses of the radar to vary widely from pulse to pulse, yielding CC values typically below 0.8. Hail and melting snow are non-uniform in shape and thus cause a scattering effect as well, but these meteorological echoes have more moderate CC values ranging from 0.8 to 0.97. Uniform meteorological echoes such as found in rain and hail yield well-behaved scatter patterns, and their CC from pulse to pulse generally exceeds 0.97.

The accuracy of the Correlation Coefficient product degrades with distance from the radar. The CC will also decrease when multiple types of hydrometeors are present within a pulse volume, thus a volume with rain and hail will yield a lower CC than the same volume with solely rain.

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Differential Reflectivity (ZDR)

The Differential Reflectivity (ZDR) product shows the difference in returned energy between the horizontal and vertical pulses of the radar. Differential Reflectivity is defined as the difference between the horizontal and vertical reflectivity factors in dBZ units. Its values can range from -7.9 to +7.9 in units of decibels (dB).

Positive values indicate that the targets are larger horizontally than they are vertically, while negative values indicate that the targets are larger vertically than they are horizontally. Values near zero suggest that the target is spherical, with the horizontal and vertical size being nearly the same. Differential Reflectivity is available in two resolutions: 8-bit at 1 degree x 0.25 km resolution and 4-bit at 1 degree x 1.0 km resolution.

Differential Reflectivity values are biased toward larger particles. Stated differently, the larger the particle, the more it contributes to the resulting reflectivity factor. Hence while raindrops are normally wider than they are tall which would tend to yield a positive ZDR value, a scattering of large hailstones in the same volume of air being observed will yield a ZDR value closer to 0, because the spherical shape of the larger objects contributes more to the final reflectivity value. If the base reflectivity product is indicating high dBZ values whereas differential reflectivity is returning values near zero, then the volume in question is likely filled with a mixture of hail and rain.

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Digital Storm Total Difference Accumulation (DSD)

Digital Storm Total Difference (DSD) shows the difference between the dual-pol product and legacy product with no bias applied. The equation used is dual-pol minus legacy. Positive values indicate the dual-pol estimate is more than the legacy estimate while negative values indicate the legacy estimate is more than the dual-pol estimate.

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Digital One Hour Difference Accumulation (DOD)

Digital One-Hour Difference (DOD) shows the difference between the dual-pol product and legacy product with no bias applied. The equation used is dual-pol minus legacy. Positive values indicate the dual-pol estimate is more than the legacy estimate while negative values indicate the legacy estimate is more than the dual-pol estimate.

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Digital Storm Total Accumulation (DSA)

Digital Storm Total Accumulation (DSA) is an estimate showing total accumulation for an event and may have bias applied. Digital Storm Total Accumulation is an 8-bit, 256 data level product available at 0.25 km * 1 degrees resolution.

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Digital Accumulation Array (DAA)

The Digital Accumulation Array (DAA) is a one-hour dual-pol based Quantitative Precipitation Estimation. Digital Accumulation Array has no bias applied meaning you are seeing raw estimates. The product is updated once per volume scan and is an 8-bit, 256 data level product available at 0.25 km * 1 degrees resolution.

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Update Interval

Collecting data is not an instantaneous process for NEXRAD radars. It takes a certain amount of time to rotate the antenna and collect data for all the different tilts. Collectively these tilts make up what is called a volume scan. Depending on whether the radar is operating in clear air mode or precipitation mode, each volume scan takes a different amount of time. When operating in precipitation mode, a volume scan takes 5-6 minutes. In severe weather mode, SAILS, MESO-SAILS, and AVSET can provide updates as quick as 72 seconds. In clear air mode, since the antenna is rotating more slowly, a volume scan takes about 10 minutes.

As a radar collects a volume scan, it first collects a 360 degree sample at an elevation angle of 0.5 degrees (tilt 1), then a scan for tilt 2, and so on, increasing elevation angle with each revolution. Once all the tilts for a given volume scan have been collected, it will recycle back down to tilt 1 and do it all over again. However, recent updates to the NEXRAD software insert an additional 0.5 degree scan in the approxmit middle of the volume scan. This new scan strategy is called SAILS.

This is why NEXRAD radar images update on a 2-10 minute interval.

RadarScope is tuned to the NEXRAD volume scan strategy and only checks for new data at times defined by the current operating mode. Checking for updates more often than that is an unnecessary waste of resources because new data will not exist until the volume scan is complete.

Resolution

RadarScope renders NEXRAD Level 2 and Level 3 data that it receives from the National Weather Service at its true resolution. Level 2 reflectivity is 250 meters by 0.5°. Level 3 reflectivity data is 1 kilometer per gate (or radar pixel) radially as you move away from the radar, and about a 1 degree angle as the radar rotates. Like a flashlight beam, the radar pulses widen as they get farther from the radar itself and the width of the pixels increases as a result. So the pulses become significantly wider and are thus lower resolution as you move away from the radar. RadarScope displays images at the true resolution of this data, so what you see is the best that NEXRAD Level 2 and Level 3 data can provide.

You’ll notice that the radar pixels become wider as you move away from the radar.

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Tilts

The radar beam is sent into the air at varying angles, or tilts, from the horizon. The lowest angle (tilt 1) is about 0.5 degrees for most radars. The highest angle (tilt 4) is between 3 and 4 degrees from horizontal. Higher tilts allow you to see higher levels of the storm structure. With any tilt, the farther the beam gets from the radar the higher it is looking in the air. Because of the steeper angle, that effect is more pronounced in the higher tilts. The curvature of the Earth also comes into play, so even if there were no tilt to the radar beam whatsoever, it is looking higher above the ground the further it gets away from the radar. Meteorologists use the higher tilts to get an idea of the vertical structure of a storm. But because of the steeper angle, those products can be a little more difficult to interpret.

For most purposes, the casual user will want to stick with tilt 1, which is closest to the ground. But keep in mind, even the lowest tilt can be sampling at thousands of feet above the ground depending on the distance from the radar. There can still be a lot of weather happening in that lowest few thousand feet beneath the beam, even for the lowest tilt.

 

Reflectivity Tilt 1

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Reflectivity Tilt 2

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Reflectivity Tilt 3

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Reflectivity Tilt 4

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You can learn more about radar tilts on this National Weather Service page:

Clear Air Mode

When there’s no precipitation in the area, it’s common for the radar to be operating in what is called “clear air mode.” In this mode, the radar is scanning more slowly so that it can be more sensitive and pick up much weaker returns. This allows it to see more details and detect finer particles in the atmosphere, including things like dust and insects.

This more sensitive mode of operation allows meteorologists to see what’s going on in the atmosphere even though no rain is falling. Clear air mode gives meteorologists the ability to see things like cold fronts and subtle airmass boundaries. When conditions are right, these boundaries can become the focal point for storm initiation, so being able to see them is extremely important. Clear air mode is also useful for detecting very light drizzle and light snow. Sometimes these phenomena do not generate a strong enough return signal to be detected in precipitation mode, but are clearly visible in the more sensitive clear air mode. For this reason, the NWS will sometimes leave a radar in clear air mode when it’s snowing.

RadarScope supports a couple of display options for clear air mode. By default, RadarScope hides the colors associated with lower reflectivity values. But if you enable “Expert Mode” in the preferences, it reveals the full color scale. This reveals more of the detail seen by the radar, but it means that what you often see is a big plume of dust, insects, and other clutter surrounding the radar. The following two images provide an example of this using the same clear air mode base reflectivity product. The first image uses RadarScope’s default color scale. The second image uses RadarScope’s expert mode color scale.

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When precipitation begins within the coverage area of a particular radar, the NWS usually switches to precipitation mode. This mode looks more like what you’d expect when looking at radar images on various web sites.

You can learn more about clear air mode on this National Weather Service page:

More Information

As you can see, there’s a lot of useful information in radar images, but interpreting them can be a tricky prospect. It takes a good understanding of how the radar works as well as how the atmosphere behaves to make sound judgements during severe weather events. The NEXRAD network offers high density coverage of the U.S., but it still can’t see everything. RadarScope is one of many tools you can use to stay informed. But it should always be used in conjunction with official information from the National Weather Service, local emergency management officials, and your local news media.

The National Weather Service has some good information on its web site about NEXRAD radar products. Here are a couple of good pages that provide starting points for learning more about NEXRAD radar:

WATCH

Does RadarScope for WATCH cost extra?

There is no additional charge for using RadarScope with your WATCH, however, a RadarScope Pro subscription is necessary.

How do I get RadarScope on my WATCH?

Make sure you have downloaded the latest RadarScope update from the App Store. Once you have done this, open the Apple Watch Companion app and chose to show RadarScope on your WATCH.

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How do I unlock the RadarScope WATCH app?

You must have a RadarScope Pro subscription for the RadarScope WATCH app to be unlocked. To purchase a RadarScope Pro subscription, open the RadarScope iOS app > tap the settings gear > tap Pro > tap the $9.99/year button. Once you have purchased Pro, the RadarScope WATCH app will be unlocked.

Unlock

How do I add favorites to use the RadarScope WATCH app?

Open the RadarScope iOS app and then tap the radar ID on the top navigation controller view. You can then tap Favorites and add your favorite radars.

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How can I view the the radar using the RadarScope WATCH app?

Tap on the desired radar site in the favorites list view of the RadarScope WATCH app. You will then see a radar image from your selected radar site.

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How do I change radar products in the RadarScope WATCH app?

You can reveal the radar products list by performing a Force Touch (longer and more forceful tap) on the WATCH screen.

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Do warnings show on the RadarScope WATCH app?

Yes! When there are active warnings, they will be shown on the RadarScope WATCH app.

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Can I see Spotter Network Spotters on the RadarScope WATCH app?

At this time, the RadarScope WATCH app does not support integration with third parties, including Spotter Network.

Does my AllisonHouse subscription work with the RadarScope WATCH app?

At this time, the RadarScope WATCH app does not support integration with third parties, including AllisonHouse.

AllisonHouse Integration

Setting Up AllisonHouse

AllisonHouse is a data aggregation and integration company that specializes in weather and weather related data. They provide various forms of weather data as part of their subscription plans.

For all questions about their services and subscription fees accompanying their service, please refer to AllisonHouse.com.

Once you have established an AllisonHouse subscription account with them, you can use there documentation to add your account RadarScope. http://support.allisonhouse.com/entries/22440844-Integrate-with-RadarScope-Mobile-iPhone-iPad-

Day 1 Outlooks

Day 1 outlooks requires AllisonHouse integration.

The following day 1 outlooks are available in RadarScope:

  • Tornado
  • Hail
  • Wind
  • Thunderstom

The Day 1 Outlooks are probability forecasts issued by an outlook forecaster at the Storm Prediction Center in Norman, Oklahoma. These forecasts are issued five times per day in 24-hour UTC or Zulu time relative to the local time at the Royal Observatory in Greenwich, England, at 0600z, 1300z, 1630z, 2000z, and 0100z. The initial update at 0600z is valid from 1200z that day until 1200z the following day, while the other reports are valid from their time of issuance until 1200z the following day.

The Day 1 Outlooks consist of an overall convective outlook for general severe weather (labeled “Thunderstorm” in RadarScope), along with individual probabilistic maps for large hail, damaging winds, and tornadoes. The convective outlook is broken into three categories:

  • Slight Risk – The threat exists for scattered severe weather including wind and hail, as well as the possibility for isolated tornadoes.
  • Moderate Risk – The threat exists for widespread or more dangerous severe weather, including numerous tornadoes and more prevalent wind damage and destructive hail.
  • High Risk – The threat exists for a major tornado outbreak with severe and life-threatening weather.

The corresponding probabilistic outlooks (tornado, wind, hail) express the likelihood of one of more events occurring within 25 miles (40 km) of any point during the outlook period. These probabilities are expressed as percentages with a wide range of values for tornadoes (2%, 5%, 10%, 15%, 30%, 45%, 60%) and a smaller range of values for hail and wind (5%, 15%, 30%, 45%, 60%). In addition to the probabilities for separate types of severe weather occurring, areas are shown where there is a 10% or greater chance of significant severe weather within 25 miles (40 km) of a given point. Significant severe weather is defined as tornadoes classified as F2 or greater (the Fujita scale), damaging winds with speeds greater than 65 knots, or large hail 2″ or greater in diameter.

Graphically, these probabilities are rendered differently depending on whether they are represented on a map as lines or shaded areas. RadarScope currently uses the former so as not to obscure additional overlays on the map. When rendered as lines, an arrowhead will be drawn, with the interior of the region indicated to the right of the arrowhead direction. The colors for line-rendered outlooks are as follows:

  • convective outlooks (thunderstorm): negligible (light brown), slight (dark green), moderate (red), high (pink/fuchsia)
  • probabilistic outlooks (tornado, hail, wind): 2% (green), 5% (light brown), 10% (dark brown), 15% (dark blue), 30% (red), 45% (pink), 60% (black), significant (blue with transverse lines, “hatched”)

The colors for outlooks represented as shaded areas (introduced in April 2011) are as follows:

  • convective outlooks
    ThunderstormOutlook
  • tornado probabilistic outlook: 2% (green), 5% (brown), 10% (dark yellow), 15% (red), 30% (pink), 45% (purple), 60% (dark blue), significant (black)
  • hail and wind probabilistic outlooks: 5% (brown), 15% (dark yellow), 30% (red), 45% (pink), 60% (purple), significant (black)

Day 1 outlook polygons are displayed directly on the map. You can zoom out and pan around the map to view these outlook polygons. Outlooks are refreshed every fifteen minutes.

 

Display Day 1 Outlook

    1. Click on “RadarScope” in the main menu bar, then click on “Preferences…”
    2. Select the outlook from the Day 1 Outlook pulldown menu.

Requires AllisonHouse integration.

For more information, see

Storm Reports

Storm reports requires AllisonHouse integration.

Storm reports are refreshed every fifteen minutes.

Reading Storm Reports

  1. Click on Info button on toolbar
  2. Select Storm Reports from the pulldown menu
  3. Click on a report in the list. The storm report text will appear in the box below the warnings list

 

You can also click on the storm report icon in the map view to see the type and time of the storm report.