Downpours and thunderstorms will spark flash flooding, damaging winds and hail across the West through early Thursday night.
Thunderstorms, some severe, will be most widespread across the Northwest and the front range of the Rockies during the late afternoon and evening on Thursday.
"Flash flooding is the main threat with these thunderstorms," AccuWeather.com Meteorologist Mark Paquette said.
Floodwater will quickly inundate some locales, particularly low-lying and poor drainage areas in the region.
"If you ever encounter a water-covered roadway, turn around and find an alternate route," Paquette said.
In addition to the flash flooding, some of the strongest thunderstorms will unleash damaging winds and hail.
In the Northwest, Yakima, Washington, and Boise and Idaho Falls, Idaho, will be among the cities at risk for locally severe thunderstorms. Casper, Wyoming, and Denver will be two of the cities in the Rockies at risk.
If you ever hear thunder, seek shelter immediately.
The skies may not appear threatening when you hear thunder, creating a false sense of security. However, if you hear thunder, you are at risk of being struck by lightning.
A slow-moving storm across the Northwest will be responsible for the locally severe weather. Along the front range of the Rockies, a stalled front will team up with monsoonal moisture.
By Friday, the risk for flash flooding will persist across the Northwest. Spotty storms will remain across the Rockies, but lower moisture will limit the potential for flash flooding and severe storms.