Periods of Heavy Rain and Snow Continue from California through the Northern Rockies; Multiple Rounds of Ice and Snow to Impact a Large Part of the Northeastern States into Next Week

Moderate to heavy rain with a flooding risk will continue for northern and central California, with heavy mountain snow in the Sierras, southern Cascades, and northern Rockies through Friday. A series of winter storms will track from the Upper Midwest to off the Northeast U.S. coast into next week bringing rounds of moderate to locally heavy rain south of their track and ice and snow to the north. Read More >

Flash Flooding/Torrential Rainfall

Biggest takeaway:
Flash flooding in particular (rapidly rising & moving water) is a very deadly threat, killing more people than many other weather threats combined. Most people die from driving into water, or being drawn to the power/unusual nature of the water - kids want to play around it & adults want to get close & take pictures. One badly placed foothold can be grabbed by the torrent and pull the person in. Camping by a small stream or river is also very dangerous when flash flooding is possible. Intense flash flooding can also create landslides.

Warning/Trigger for Plan:
NWS Flash Flood Warning
…also may need actions for NWS Flood Warning (though inundation more gradual)

Advance Notice/Time to Activate & Accomplish Your Planned Response:
Typically 30-60 minutes

Frequency:
~0-5/year at various times of day & night.

How Accurate Warnings?
If there is flash flooding, there almost certainly will be a Flash Flood Warning issued beforehand. That said a little more than 1/3 are false alarms.

Identify any low areas, drainage areas, small streams. With a 1 in 100 year rain storm, these could all quickly (in a few 10s of minutes) turn from barely noted afterthoughts to large, raging torrents of water carrying anything they touch downstream. Even though these areas may have never caused problems before, with enough rain, they all could become deadly threats very quickly.
The biggest protective actions you can take are to:
- Know potential danger zones
- Be able to monitor them
- Get people away from them quickly, and keep them away (barricades/tape/personnel)
Note: Any NWS Flash Flood Warning will quickly activate the Wireless Emergency Alert system and alert the cell phones of most of the people in your location. The message will be short, only saying "Flash Flooding expected in your area until xx:xx [time]". But that short message will likely impact their response and awareness, and needs to be taken into account in your plans.
In addition to Flash Flood Warnings, the NWS issues Flood Warnings for more gradual inundation. These are more common, do not activate Wireless Emergency Alerts on people's phones, and are typically more water management issues than deadly threats. That said, you should monitor conditions and be ready to activate your Flash Flooding plan if necessary.