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RadarScope is a specialized display utility for weather enthusiasts and meteorologists that allows you to view NEXRAD Level 2 radar data and severe weather warnings. It can display the latest reflectivity, velocity, and other radar products from any NEXRAD radar site in the United States, Guam and Puerto Rico. These aren’t smoothed PNG or GIF images, this is real Level 2 radar data rendered in its original radial format for a high level of detail.

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RadarScope Help

Radar Products

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.

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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 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:

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 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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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.

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

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:

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:

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:

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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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:

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.

 

Base Reflectivity Tilt 1

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Base Reflectivity Tilt 2

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Base Reflectivity Tilt 3

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Base Reflectivity Tilt 4

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

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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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 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.

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:

Terminal Doppler Weather Radar

Terminal Doppler Weather Radar (TDWR) were developed to detect hazardous wind shear conditions for aviation. There are currently 48 TDWR stations in the United States. They are generally located on or near major airports.

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The TDWRs have a different product set than the standard NEXRAD Radars.

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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Dual-Pol Products

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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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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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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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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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, here are the steps to integrate it into RadarScope:

  • Open http://allisonhouse.com/rs/customer/ using your web browser.
  • Log in using your AllisonHouse username and password.
  • Tap the “Click Here to Load Account Info into RadarScope” link.

This link will re-open RadarScope with your account settings. Once your account has been activated, follow these steps to enable the various AllisonHouse data types:

  • Click the Info button (bottom right corner).
  • Select “Inspector” from the pulldown menu on the top right of the window.
  • Select “AllisonHouse” from the Data Provider list under “Radar Data”

Storm Reports

Storm reports requires AllisonHouse integration.

Storm reports are refreshed every fifteen minutes.

Read 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.

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 (thunderstorm): negligible (light green), slight (yellow), moderate (red), high (pink)
  • 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.

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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

FAQ

What is RadarScope?

RadarScope is a specialized browser for the National Weather Service’s NEXRAD Level III public data feed.

What does it do?

It retrieves the latest available data from NOAA’s NWS server for a single radar site and displays it on a map. It can display base reflectivity, base velocity or storm relative velocity data at the lowest tilt angle.

What does it not do?

It does not provide a a broad national overview of all precipitation in the US, or what are called radar mosaics.

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.

Does it work for Puerto Rico?

Yes! RadarScope 1.4 adds support for the San Juan, Puerto Rico radar.

Does it work for Hawaii, Alaska, or Guam?

Yes! RadarScope 1.7 adds support for radars in Hawaii, Alaska, and Guam.

Does it display animated loops?

Yes. RadarScope can download and animate over the latest six frames of data.

Where does the data come from?

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

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://weather.noaa.gov/monitor/radar/ orhttp://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.

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.

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 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.

Does the sweep animation indicate refreshed data?

No. The sweep animation is intended to depict the coverage area of each radar to help you determine which radar best covers your area of interest. It is not an indication of refreshed data.

The radar buttons and “sweep” animations on the map are distracting. Is there any way to hide them?

Yes. Touch the “Change Radar” button, which is the second button from the left in the toolbar, to show or hide the radar buttons and sweep animations.

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. You can see the bands of light drizzle to the east, which are approaching levels that would trigger a switch over to precip mode by the radar operator.

What is Doppler radar?

A great place to start learning about Doppler radar is athttp://www.srh.noaa.gov/radar/radinfo/radinfo.html. Additional information is available athttp://www.srh.noaa.gov/jetstream/doppler/radarfaq.htm

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.

What features are you going to add and when will they be available?

We have many feature requests, and we are continuing to support and improve RadarScope. Because of the uncertainties associated with software development, we prefer not to make commitments regarding new features and when they might be available.

We invite you to follow us on Facebook or Twitter @RadarScope for the latest news and info regarding the product.

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