What Radar Actually Shows
Doppler weather radar sends out pulses of energy that bounce off precipitation — rain, snow, hail, and sometimes debris. What you see on a radar map is reflectivity: how much energy bounced back. More energy = heavier precipitation = brighter colors.
The radar does NOT show clouds, fog, drizzle, or wind by itself. It shows precipitation intensity and, with Doppler capability, the motion of that precipitation toward or away from the radar site.
What the Colors Mean
Radar color scales vary by app, but the standard NWS reflectivity scale follows this pattern:
Green — Light to Moderate Rain
Light green is light rain or drizzle. Dark green is moderate, steady rain. You'll get wet but it's not dangerous.
Yellow — Heavy Rain
Heavy rain that can reduce visibility. In a sustained band, this can cause localized flooding. Pay attention.
Orange — Very Heavy Rain
Intense rainfall. Possible small hail. If you see a compact orange core, that's a strong thunderstorm cell.
Red — Extreme Rain / Hail
Extremely heavy rain, likely hail. Red cores inside thunderstorms are where the worst conditions are. Severe weather is likely.
Purple / White — Giant Hail or Tornado Debris
The most intense returns. In a supercell, this can indicate giant hail (2"+) or even a tornado debris signature (TDS). Take shelter.
How to Spot Dangerous Storms
Hook Echo
A hook-shaped appendage on the south side of a storm cell. Classic signature of a rotating supercell, often associated with tornadoes. If you see one near you, take shelter.
Bow Echo
A line of storms that bows outward. Indicates powerful straight-line winds (60–100+ mph) called a derecho. Can be as destructive as a tornado across a wider area.
Training Echoes
Multiple storm cells moving over the same area in a line, like train cars on a track. Causes extreme rainfall and flash flooding even if individual cells are moderate.
High-Reflectivity Core
A bright red/purple/white core inside a storm indicates large hail. The brighter and more compact, the bigger the hail. 2"+ hail can shatter windshields.
Tips for Reading Radar
Use the Loop
A single frame tells you where rain is. The animation loop tells you where it's going. Always watch the loop to see storm motion and speed.
Check the Timestamp
Radar images can be 5–10 minutes old by the time you see them. Fast-moving storms may be miles ahead of where the radar shows.
Zoom In
National views are good for the big picture, but you need to zoom into your county to see individual storm cells and their structure.
Reflectivity vs. Velocity: Two Different Views
Everything above describes reflectivity mode, which shows precipitation intensity — the standard "radar map" view. Meteorologists also use a second mode called velocity, which shows how fast precipitation is moving toward or away from the radar site, color-coded (typically green for motion toward the radar, red for motion away). A tight, adjacent red-and-green pairing in velocity mode — a "couplet" — is one of the clearest radar signatures of rotation, often visible before a hook echo appears in reflectivity. Most consumer weather apps only show reflectivity, but knowing velocity exists helps explain why professional meteorologists sometimes issue a tornado warning based on radar alone, before any visual confirmation.
Frequently Asked Questions
Why does radar sometimes show rain where it isn't actually raining?
Radar detects anything that reflects its pulses, including virga (rain that evaporates before reaching the ground), and can occasionally pick up non-weather returns like birds, insects, or ground clutter near the radar site.
What's the difference between base and composite reflectivity?
Base reflectivity shows a single radar elevation angle (usually the lowest, closest to the ground). Composite reflectivity shows the strongest return at any altitude in the storm's column, which can reveal hail cores aloft that haven't reached the surface yet.
Can radar see through mountains?
No — radar beams travel in straight lines and can be blocked by terrain, creating coverage gaps behind mountains. This is a known limitation in parts of the Mountain West and Appalachians.
Why does radar coverage get worse far from a radar site?
The radar beam gradually rises above the ground with distance due to the curvature of the Earth, so far from a radar site, the beam is scanning higher in the atmosphere and can miss shallow, low-altitude features like a developing microburst.
Live Radar on Your Phone
StormCast includes live interactive radar with storm cell tracking and NWS warning polygons overlaid so you can see exactly what's warned and what's heading your way.
More from the Blog
A note on this guide: Thresholds and criteria described here are general and can vary by NWS forecast office, region, and over time. This content is educational — always check your local National Weather Service office for the specific criteria that apply to your area.