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PERILRADAR

Peril Wall

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Live radar is switching on

The NOAA radar loop, radar-estimated hail, 24-hour rain and the official 7-day rainfall forecast arrive on this map shortly.

  • Radar loop · NOAA MRMS
  • Hail & rain · radar-estimated
  • Rain ahead · NOAA WPC

Warnings on the map are live now, reprinted from the National Weather Service.

How to read this map

Each tab is one layer. The legend in the map's corner is drawn from the same colour table as the map, so the two can never disagree. Every layer says where it comes from and whether it is a measurement, a radar estimate or an official forecast that we reprint. PerilRadar issues no warnings and computes nothing about future weather.

Live radar FACT

Radar reflectivity in dBZ — how much energy the rain, snow or hail sends back to the radar. Higher means heavier. It is NOAA's MRMS composite: every US weather radar blended into one national picture, about the last two hours on a loop.

  • 5–20 dBZlight rain, drizzle or light snow
  • 30–40 dBZmoderate to heavy rain
  • 45–55 dBZvery heavy rain, strong storms
  • 60–65 dBZintense cores, often with hail aloft
  • 70+ dBZextreme cores

A new frame about every 4 minutes. The badge shows how old the newest frame is; it says Delayed when NOAA has not posted a newer file for more than 15 minutes.

Hail 24 h ESTIMATE

Radar-estimated hail size in inches: NOAA MRMS MESH (Maximum Estimated Size of Hail), the largest value at each spot over a rolling 24 hours. It shows where to look, not what landed — spotter and ground reports are the measurement.

  • 0.25–0.75 insmall hail
  • 1.00 inquarter size — the National Weather Service severe-hail size
  • 1.50–1.75 inping-pong to golf ball
  • 2.50–2.75 intennis ball to baseball
  • 3.5–4+ insoftball and larger

NOAA updates the 24-hour maximum through the day; the badge shows the time of the file on the map.

Rain 24 h ESTIMATE

Radar-estimated rainfall in inches over the 24 hours ending at the frame time: NOAA MRMS multi-sensor estimate, radar corrected with rain gauges where NOAA has them. Not a gauge reading.

  • 0.01–0.25 ina trace to a light soaking
  • 0.5–1 ina solid rain
  • 2–4 inheavy, flooding possible on poor drainage
  • 5–10 inextreme totals
  • 15–20+ intropical-system totals

Hourly. NOAA posts the gauge-corrected pass about an hour after the hour ends.

Rain ahead FACT

The official NOAA Weather Prediction Center rainfall forecast for day 1, days 1–3 and days 1–7, in inches, reprinted exactly as issued. The same colour scale as Rain 24 h. Each number is the lower bound of a WPC band, so “2.00+” means the band from 2 inches up.

WPC issues it several times a day; the badge shows the issue time and the strip shows the end of the period.

Warnings FACT

Tornado, severe thunderstorm, flash flood, extreme wind and snow squall warning polygons exactly as the issuing National Weather Service office drew them, reprinted with credit and checked every minute. Tap one for the office and the expiry time.

FACT, ESTIMATE and MODEL

FACT is official data shown as the agency published it, with its source: the radar measurement, the NWS warnings and the WPC rainfall forecast (official, reprinted — not ours). ESTIMATE is a NOAA product that infers something the radar cannot measure directly, such as hail size or rain at the ground. MODEL marks computer-model output, such as the optional wind-flow layer from NOAA's GFS. Nothing on the wall is computed by PerilRadar and passed off as an observation.

Where the data comes from

  • MRMS — NOAA's Multi-Radar Multi-Sensor system, run by the National Severe Storms Laboratory and the National Weather Service, blends about 180 radars with gauges and models into national grids. Live radar, Hail 24 h and Rain 24 h all come from it. NSSL: MRMS ↗
  • MESH — Maximum Estimated Size of Hail, an MRMS product computed from the radar volume above the freezing level. NSSL radar research ↗
  • WPC — NOAA's Weather Prediction Center issues the official US quantitative precipitation forecast that the Rain ahead tab reprints. WPC rainfall forecasts ↗
  • NWS warnings — read from the National Weather Service alerts service and reprinted with the issuing office named. NWS API ↗
  • Address lookup — US Census Bureau geocoder, no key, no tracking. Census geocoder ↗
  • Base map — US Census county and state lines (public domain) via us-atlas, Natural Earth coastlines (public domain), street detail when zoomed in from OpenFreeMap / OpenStreetMap contributors. Map engine: MapLibre GL JS (BSD-3).

What the Peril Wall is not

It is not a warning service and not a forecast of ours. It reprints official NOAA and National Weather Service data with credit, labels radar estimates as estimates, and says plainly when a source is late or offline. If you are in a warned area, follow the National Weather Service and your local officials. A quiet board — no warnings in effect — is a healthy state, not a broken page.

Storm Replay and address alerts

Everyone can replay the last two hours of radar. Members can open earlier storm days from the archive — one NOAA radar frame every 10 minutes, the last 7 days, always labeled with the date — and save up to five addresses for email alerts when an official NWS warning covers the point or radar-estimated hail of 1 inch or larger shows up within about 2 km. See membership and how the site works.

Peril Wall questions

Where does the radar on the Peril Wall come from?

From NOAA's Multi-Radar Multi-Sensor system (MRMS), which blends every US weather radar into one national grid. The loop shows about the last two hours, newest frame last, and the badge says how old the newest frame is.

How old is the radar on the map?

A new frame arrives about every 4 minutes and is usually a few minutes behind real time. The badge shows the age of the newest frame and switches to Delayed when NOAA has not posted a newer file for more than 15 minutes.

Is the hail layer a measurement?

It is a radar estimate, labeled ESTIMATE: NOAA MRMS MESH, the maximum expected hail size the radar volume supports, over a rolling 24 hours. Ground reports from spotters are the measurement; MESH shows where to look.

Does PerilRadar make its own rain or storm outlook?

No. Rain ahead is the official NOAA Weather Prediction Center rainfall forecast, reprinted with credit. PerilRadar computes nothing about future weather.

Who issues the warnings drawn on the map?

The National Weather Service office named on each warning. PerilRadar reprints the polygon and headline exactly as issued, with credit. If you are in a warned area, follow the NWS and local officials.

Why do I see a still image before the map starts?

On phones the live map engine loads only when you tap Start the live map, so the page opens fast and uses no data you did not ask for. The still image is a real capture of the wall, labeled not live with the radar time it shows.

How much data does the radar loop use on a phone?

On phones the loop uses smaller frames and downloads only when you press Play; the newest frame loads first. The hint next to Play shows the number of frames and their size.

What is Storm Replay?

Scrubbing back through past radar. Everyone can replay the last two hours. Members can open earlier days from the archive: one NOAA radar frame every 10 minutes for the last 7 days, always labeled with the date and never as live.

How do address alerts work?

Members save up to five addresses. An email goes out when an official NWS warning covers the point, or when radar-estimated hail of 1 inch or larger shows up within about 2 km. Each alert names its source, and a Send test button shows what one looks like.

What do members get on the Peril Wall?

Alerts for saved addresses, hail history for an address and Storm Replay of past storm days. The live map, the boards and the address card stay free.

Watch a roof, not just a map

Members get alerts for a saved address, its hail history and Storm Replay.

See membership