From NOAA/NWS: 

"

Interactive NWS Alert

New event: Flash Flood Watch for Whatcom County, WA, Skagit County, WA, Snohomish County, WA
Sent via Email at 938 am PDT, Jul 31st 2025

Radar valid at 954 am PDT, Jul 31st 2025

Thunderstorms will develop over the Cascades this afternoon and tonight. Storms will be slow-moving and produce high rain rates, allowing for potential flash flooding over area burn scars.

WAZ301-305-010545-
/O.NEW.KSEW.FF.A.0001.250731T1900Z-250801T1200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Cascades of Whatcom and Skagit Counties-Foothills and Valleys of
the North Cascades-
Including Mount Baker, Granite Falls, Sudden Valley, and
Darrington
938 AM PDT Thu Jul 31 2025

...FLASH FLOOD WATCH FOR THE SOURDOUGH BURN SCAR IN EFFECT THROUGH
LATE TONIGHT...

* WHAT...Flash flooding and debris flows caused by excessive
rainfall are possible over the Sourdough burn scar.

* WHERE...A portion of northwest Washington, including the following
areas, Cascades of Whatcom and Skagit Counties and Foothills and
Valleys of the North Cascades.

* WHEN...Through late tonight.

* IMPACTS...Heavy rainfall over the Sourdough burn scar is expected
up to and during the period of the watch. Residents or travelers
near the Sourdough burn scar should prepare for potential flooding
impacts. Be sure to stay up to date with information from local
authorities. Heavy rainfall could trigger flash flooding of
low-lying areas, urbanized street flooding, and debris flows in
and near recent wildfire burn scars.

* ADDITIONAL DETAILS...
- National Weather Service Meteorologists are forecasting heavy
rainfall over the burn scar, which may lead to flash flooding
and debris flows.
- http://www.weather.gov/safety/flood

PRECAUTIONARY/PREPAREDNESS ACTIONS...

You should monitor later forecasts and be prepared to take action
should Flash Flood Warnings be issued."