Above-normal temperatures will continue through Friday before a significant pattern change brings cooler, wetter weather for the weekend and into next week. Expect widespread showers and thunderstorms, with the potential for heavy rain, gusty winds, and small hail.
Warmth Continues Before the Storms
Southerly flow aloft will keep temperatures warm through Friday, with highs reaching the 60s and 70s across the region. The Snake River Basin will see the warmest temperatures. However, the pleasant weather will be short-lived as a Pacific upper-level low slowly approaches northern California.
Scattered showers and isolated thunderstorms will begin developing in southeast Oregon and along the Idaho-Nevada border late Thursday afternoon and evening.
Active Friday Night and Saturday
By late Friday, a stronger low-pressure system from the Gulf of Alaska will overtake the initial Pacific low. This combined system will push moisture inland and northward, resulting in widespread showers and evening thunderstorms across the region.
The greatest instability for strong thunderstorms will occur Friday evening, particularly in Owyhee and Twin Falls counties, where storms could produce hail and gusty winds. However, all areas will have enough instability to support thunderstorm development.
Numerous showers will continue through Saturday and Saturday night, though the threat of severe thunderstorms will decrease as cooler surface temperatures stabilize the atmosphere.
Heavy Rain and Cooler Temperatures Sunday
Later Saturday night, the stronger upper low will reach the northern California coast, sending another surge of moisture into the area from the south. This surge looks even wetter than Friday night's and will bring widespread showers and a 15 to 25 percent chance of thunderstorms throughout Sunday.
Rainfall totals from Friday night are estimated at 0.25 to 0.50 inches, with localized amounts up to 1 inch in the Owyhees and on Steens Mountain. From Saturday night through Sunday, southeast Oregon could see 0.50 to 1.00 inch of rain, while western Idaho can expect 0.25 to 0.75 inches.
Temperatures will drop significantly over the weekend, cooling about 10 degrees on Saturday and another 5 degrees on Sunday. Valley highs will only reach the mid to upper 50s by Sunday and Monday.
Mountain Snow and Next Week's Outlook
Snow levels will drop to 5,000 to 6,000 feet late Sunday and 4,000 to 5,000 feet on Monday night, with snow accumulations largely limited to higher peaks.
The low-pressure system will exit the region by early Tuesday, bringing a brief return to mostly dry conditions and mild temperatures. However, shower chances quickly return Wednesday as another trough deepens into the region from British Columbia, bringing much colder air and precipitation late Wednesday into Thursday.
Tonight
Mostly cloudy, with a low around 49. Northwest wind 5 to 7 mph becoming calm in the evening.
Friday
Scattered showers before 4pm, then scattered showers and thunderstorms between 4pm and 5pm, then showers likely and possibly a thunderstorm after 5pm. Partly sunny, with a high near 73. Light wind could be gusty near late-day storms. Chance of precipitation is 60%.
Friday Night
Showers and possibly a thunderstorm before 2am, then showers between 2am and 5am, then showers and possibly a thunderstorm after 5am. Low around 49. Locally breezy winds. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
Saturday
Showers and possibly a thunderstorm before noon, then a chance of showers and thunderstorms between noon and 5pm, then showers likely and possibly a thunderstorm after 5pm. High near 65. Light wind. Chance of precipitation is 80%.
Saturday Night
Showers. Low around 45. Light wind. Chance of precipitation is 90%. New precipitation amounts between a tenth and quarter of an inch possible.
Sunday
Showers, with thunderstorms also possible after noon. High near 58. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.
Sunday Night
A 50 percent chance of showers. Mostly cloudy, with a low around 41.
Monday
A 50 percent chance of showers. Partly sunny, with a high near 56.
Monday Night
Mostly cloudy, with a low around 38.
Tuesday
Mostly sunny, with a high near 58.
Tuesday Night
Partly cloudy, with a low around 40.
Wednesday
A 30 percent chance of showers. Partly sunny, with a high near 58.
Wednesday Night
A 20 percent chance of showers. Mostly cloudy, with a low around 36.
Thursday
Mostly sunny, with a high near 56.
