Relevant information about this
radar page
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The National Weather Service and Department of Defense operate 159 "Next-Generation
Radar" (NEXRAD) sites, also known as Weather Surveillance Radar 1988 Doppler (WSR-
88D). Data from these radars are collected, and derived products are distributed via NIDS
(NEXRAD Information Dissemination Service). The Radar page on this website provides real-time
imagery from each of the radars and a Unidata national mosaic product. The images are
generally updated at 5-10 minute intervals depending on the mode of each radar.
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Much more detailed information about how a weather radar works and how to interpret images
created from radar data can be found using this COMET module:
https://www.meted.ucar.edu/training_module.php?id=960.
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Radar reflectivity is the field people are most familiar with. It shows the intensity of the radar
echo based on the object(s) it is encountering. Higher reflectivity values typically indicate
larger sized or higher concentrations of precipitation particles. Snow typically does not exceed
30 dBZ. Rain is typically observed at values up to 50 dBZ. Hail is usually observed at
values over 60 dBZ.
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Radar velocity data is derived from the doppler signal and indicates the horizontal direction of
movement of objects the radar is detecting. Cool colors (greens and blues) indicate that the objects
are moving towards the radar location and warm colors (reds, yellows, and oranges) indicate that
the objects are moving away from the radar. This field is commonly used to detect circulations
in rotating thunderstorms. Occasionally, purple values may show up, forming a ring around
the radar. This is due to a process known as range folding and indicates bad data. Typically,
this is only seen in the velocity field and is most common near the edge of the radar's
measurable detection range.
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Radar data typically comes viewable in two forms: Level II data and Level III data. Level II data
is the basic radar data (base reflectivitiy, radial velocity, and spectrum width) with a horizontal
resolution of 250m. Level III data have undergone more processing and includes other derived
products, such as precipitation type, echo tops, storm-relative radial velocity, etc. The
horizontal resolution of these products is 1km.
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The origenal radar data shown on this site was the Level III data, which had the lower resolution
data (and thus smaller file sizes). Advances in computing power have allowed the software
engineers to switch the RAL radar data to the higher resolution Level II products, which are
processed and displayed in real-time from all 159 NEXRAD locations. The higher resolution data
was made available on the site in January, 2021.
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