How it works

You add the site. We watch every forecast for it.

QPE Assistant checks the National Weather Service forecast for each of your sites every hour. When the forecast meets the QPE rule, you know days ahead, with the start time, the amount and a record of how the forecast got there.

The four steps

  1. 1Once

    Add your site

    Type an address or the nearest intersection, then drag the pin if the site isn’t exactly there.

    1450 Owens St, San Francisco
  2. 2Instantly

    We find its NWS grid point

    The Weather Service forecasts on a grid of about 2.5 km squares. Your pin picks the square, and nearby sites can share one.

    Near San Francisco, CA · grid MTR 88,126
  3. 3Every hour, :45

    We check the new forecast

    Each hour we pull the 7-day hourly forecast for every grid point and run the QPE rule on it. Every update is saved.

    QPE Mon 12 AM · 0.92 in · 85%
  4. 4Your hour

    You and your inspectors hear about it

    A daily email at the hour you pick: the full report, or a short note on days with no QPE. Inspectors get a copy with just their sites.

    Daily report · 7:00 AM · full report on QPE daysDaily report · 7:00 AM

The QPE rule, exactly

A qualifying precipitation event (QPE) under the 2022 Construction General Permit. We apply it to the forecast in 6-hour steps, looking at the next 24 hours each time.

Startswhen the next 24 hours are forecast to bring 0.5 in or more and the chance of rain is 50% or higher.
Continueswhile each following 24 hours still brings 0.25 in or more.
Inspectwithin the 72 hours before it starts (Risk Level 2 and 3). Turn on the pre-inspection window to see it on every report.

An event still running at the end of the 7-day forecast is shown as "after forecast ends", with its total so far.

Example: one site, one 7-day forecastSample numbers
QPE
Pre-inspection, 72 h
0.50 in · start
0.25 in · keep going
Starts · 0.62 in, 70% Still ≥ 0.25 in Ends · 0.14 in 1.0 in 0
50%
SatSunMonTueWedThuFri
Forecast rain, next 24 hours Chance of rain, each 6 hours
Example: one 7-day forecast Sample numbers
SatSunMonTueWedThuFri
QPE Pre-inspection, 72 h 0.50 in

Bars: forecast rain in the next 24 hours at each 6-hour step. The event starts Mon (0.62 in, 70%) and ends Wed when the 24-hour total drops below 0.25 in.

What to expect, day by day

  1. Sign-up Add your first site freeConfirm your email, then the guide walks you through the address, the pin and who gets reports. No card needed for one site.Confirm your email, then add the address and who gets reports. No card needed for one site.
  2. Within the hour Your first forecast appearsIf another site already shares the grid point, it’s there right away. Otherwise it arrives with the next hourly check.
  3. Every morning The daily reportAt the hour you pick. Get the full report every day, or only when there’s a QPE, with a one-line “no QPE” note on quiet days so you know the check ran.At the hour you pick, full or only on QPE days with a one-line note on quiet days.
  4. Up to 7 days out A QPE shows upThe site turns blue on your Sites page, with the start time, the event total and how many hours away it is.
  5. 72 h before Pre-inspection window opensIf the setting is on, the report highlights the window in amber so crews know when to go.If the setting is on, reports highlight the window in amber so crews know when to go.
  6. As forecasts change Every update is keptStarts move and totals grow or shrink. The site’s history shows each change, so you can show what the forecast said and when.Starts move and totals change. The site’s history shows each change.

Questions people ask

Why a grid point and not my exact address?

The Weather Service publishes its forecast on a grid of roughly 2.5 km squares. We use the square under your pin, so two sites in the same square get the same forecast. You’ll see the grid point and the nearest town on every site.The Weather Service publishes its forecast on a grid of roughly 2.5 km squares. We use the square under your pin, so two sites in the same square get the same forecast.

Does it measure the rain that actually fell?

No. QPE Assistant works from forecasts, so you can plan before the storm. Keep using your rain gauge or permit-required records for what actually fell.

What if the Weather Service is down?

We keep showing the last forecast we have and put a banner at the top of every page saying how old it is. We keep checking every hour and update as soon as a new forecast arrives.

Who gets the daily email?

You do, at the hour you pick. Choose the full report every day, or the full report only on QPE days and a short “no QPE” note otherwise. Each inspector you add gets their own copy with only the sites you assign them.

Can I see how the forecast changed?

Yes. Every hourly update is saved, and each site has a forecast history: a list of past events and a calendar, with when each QPE was first flagged and whether it held.

How far ahead will I know?

Up to 7 days, the length of the NWS forecast. How early a QPE shows up depends on the storm; the forecast history shows the lead time for each past event.

Useful links

CA State Water Resources Control Board 2022 Construction General Stormwater Permit (CGSP) State Water Resource Control Board 2022 CGP Road Show Presentation NOAA Weather NWS Weather Table California SMARTS Database

Try it on one of your sites.

One site free, no card. Your first forecast shows up within the hour.

See pricing Start free evaluation