A significant pattern change is underway as a potent upper-level low and cold front move into the region Friday morning, bringing widespread showers, scattered thunderstorms, and a dramatic temperature drop that will push readings to around 20 degrees below normal by Saturday.
The cold front will cross the area Friday morning, bringing light showers and gusty winds. Partial clearing behind the front in the afternoon will allow for the development of scattered thunderstorms. Storms are expected to initiate across southeast Oregon around noon, then track eastward into southwest Idaho late Friday afternoon and early evening.
Despite increasing moisture aloft, low levels will remain quite dry through at least early Friday evening, increasing the risk for strong, erratic outflow winds from any storms. The lower levels will eventually moisten up overnight, with storms transitioning to a threat for brief heavy rain and small hail. This heavy rain threat will be most pronounced by Saturday morning as the bulk of the convective activity shifts into southwest Idaho.
As the center of the low moves into the region on Saturday, shower and thunderstorm activity will focus heavily across southwest Idaho. Moisture values are forecast to peak around the 90th percentile Saturday morning, supporting storms capable of producing brief heavy rain through Saturday evening. Precipitation amounts of up to 1 to 1.25 inches are possible over the central Idaho mountains, while the Snake River Plain will generally see between 0.25 and 0.50 inches. Temperatures will plummet to around 20 degrees below normal on Saturday, with several locations forecast to approach record low maximum temperatures for the day.
A low-pressure system over the Northern Rockies will continue to bring cool and showery conditions on Sunday, especially for west-central and central Idaho. Snow levels will temporarily lower to 6,500 to 7,500 feet Sunday morning, allowing light snow to fall across the high terrain. Gusty winds will develop in the afternoon while temperatures remain 15 to 20 degrees below normal. Conditions will trend a little warmer Monday as the low gradually departs, though unsettled conditions will linger across the Northwest through Wednesday as a secondary low approaches from British Columbia.
Tonight
A 20 percent chance of showers after midnight. Mostly cloudy, with a low around 60. Northwest wind 5 to 13 mph.
Friday
Showers likely, with thunderstorms also possible after noon. Cloudy, with a high near 74. Northwest wind 5 to 14 mph becoming south in the afternoon. Winds could gust as high as 23 mph. Chance of precipitation is 70%.
Friday Night
Showers and possibly a thunderstorm. Low around 52. South southeast wind 5 to 9 mph becoming west northwest after midnight. Chance of precipitation is 80%. New rainfall amounts between a quarter and half of an inch possible.
Saturday
Showers and possibly a thunderstorm before noon, then a chance of showers and thunderstorms after noon. Patchy fog between 7am and 9am. High near 67. West northwest wind 5 to 15 mph, with gusts as high as 24 mph. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.
Saturday Night
Mostly cloudy, with a low around 46. Northwest wind 7 to 13 mph.
Sunday
A 20 percent chance of showers. Partly sunny, with a high near 67.
Sunday Night
Mostly cloudy, with a low around 47.
Monday
Mostly sunny, with a high near 74.
Monday Night
Partly cloudy, with a low around 50.
Tuesday
Sunny, with a high near 80.
Tuesday Night
Mostly clear, with a low around 51.
Wednesday
Sunny, with a high near 82.
Wednesday Night
Mostly clear, with a low around 54.
Thursday
Sunny, with a high near 88.
