LeadTime
How it works

From a radar picture to “rain in 40 minutes”

Most weather apps show you a radar map and leave the thinking to you. LeadTime does the thinking, and shows its work.

1. The radar

LeadTime uses NOAA's MRMS mosaic — a quality-controlled composite of every weather radar in the country, updated every two minutes. Quality-controlled matters: raw radar is full of ground clutter, birds and sun spikes that look like rain. MRMS removes them, so a clear sky looks clear.

2. Tracking the storms

Each new frame is compared with the previous ones. LeadTime measures how the rain pattern has shifted — overall and region by region — to get a motion vector: direction and speed for the storms near you. It also labels each rain cell and follows it from frame to frame, so it knows whether a cell is strengthening, holding, or weakening.

3. Hit or miss

With motion known, every cell is projected forward along its track. If a cell's path crosses your spot (within a few miles — you choose), that's a hit, and the arrival time comes from distance and speed. If its path passes beside you, LeadTime says so: “Rain 18 mi SW, passing to the north.” If a cell is weakening fast enough that it would die before it reaches you, you get “weakening — may fizzle” instead of a false alarm.

Times are rounded the way people actually say them: “just over an hour”, “just under 40 minutes”. Under ten minutes you get the exact number.

4. Lightning and official warnings

Lightning comes from the GOES satellites' Geostationary Lightning Mapper, which sees every flash over the US. You get counts within 10, 20 and 30 miles and whether the strikes are approaching. National Weather Service alerts for your exact location are checked every few minutes; tornado, severe thunderstorm, flash flood, flood, hurricane, tropical storm, storm surge, extreme wind, tsunami, blizzard, ice storm, winter storm, extreme cold and avalanche warnings always sound, even if you've snoozed the rain chime.

5. Everything else on one map

River gauges in flood, wildfire perimeters and smoke, satellite cloud, wind arrows, tropical cyclone tracks, topographic maps and hiking trails — each a layer you can switch on. Tides and water temperature for the beach; snow depth from the nearest SNOTEL site for the slopes.

How accurate is it?

Honest answer: it depends on the storm.

  • Organised systems — fronts, squall lines, big thunderstorm complexes — move predictably. Arrival times an hour out are usually within 10–15 minutes, and tighten as the storm gets closer.
  • Pop-up summer showers form, drift and dissolve in 20 minutes. Nobody tracks those well. LeadTime flags low confidence and leans on the NWS hourly forecast for the probability.
  • Mountains bend storm tracks and block radar beams; expect wider error bars in deep valleys.

LeadTime extrapolates the last hour of radar; it does not run a weather model. That's the right tool for the next two hours, which is when a tent or an awning needs the answer. For tomorrow, it uses the NWS forecast.

LeadTime supplements official warnings; it never replaces them. It relays NWS alerts but can miss them if your connection drops. For severe weather, keep a NOAA weather radio or your phone's emergency alerts on as well.

Privacy, briefly

The free web app sends your location to NOAA and the NWS to fetch your forecast, and nowhere else. With alerts turned on, your location is stored on LeadTime's server so it can watch the radar for you; turn alerts off and it's deleted. There are no ads and no tracking. Full privacy policy.