RainClock turns a public rainfall grid into per-site inspection deadlines. The steps below are the whole method. If you disagree with a number, this page should tell you exactly where it came from.
1. The data
NOAA MRMS Multi-Sensor QPE: a national grid at roughly 1-kilometre resolution, combining radar with gauge observations, published hourly with about an hour of latency. It is public data, free to anyone. Source: mrms.ncep.noaa.gov.
2. Sampling a site
A site is a coordinate, not a cell. We take the grid cell containing the site and also the maximum of the eight surrounding cells. The nearest cell is the reading; the neighbour maximum tells us whether the site sits near a cell boundary during a sharp storm.
3. Deciding an event
The reading is compared against your election's trigger — 0.25″ under the EPA CGP, 0.5″ under TXR150000, per-site variants for arid areas. Two outcomes:
- Confirmed: the nearest cell crosses the trigger cleanly. The 24-hour clock opens and you get the alert.
- Possible: only the neighbours crossed it, or the nearest cell was missing. It shows on your site page as “possible event, check your gauge”. It does not open a clock.
The asymmetry is deliberate. A fabricated obligation is worse than a missed one, so when the data is ambiguous we say so instead of manufacturing a deadline. Once you are on the log the ambiguity is still shown to you, because your gauge may know something the radar does not.
4. What we never do
- Backfill storms from before a site is on the log. History accrues forward.
- Decide your schedule election, or assert that you were required to inspect.
- Perform, sign, or certify an inspection. Your qualified person does that.
- Share your binder with any agency. It is yours.
Limits worth stating plainly: MRMS covers the continental United States, radar estimates are estimates, and a cell is about a kilometre across. That is why every rain figure in this product names its source and its fetch time, and why the gauge-override path exists on every event.