The Treasure Valley will enjoy one more warm and beautiful day Saturday before a powerful cold front sweeps through Saturday night, delivering a dramatic temperature drop, gusty winds, and showers to the central Idaho mountains Sunday.
Dramatic temperature changes arrive during the weekend in Scott Dorval's video forecast
Saturday: Warm and Mostly Sunny with Afternoon Smoke
Saturday will be a warm and mostly sunny day with a high near 86 degrees, running about 5 to 8 degrees above the normal high for mid-September in Boise. Southwesterly flow aloft will tap into warm air and push temperatures well above seasonal averages. However, wildfire smoke from fires in California will be transported northeastward, leading to increasing haziness across southwest Idaho Saturday afternoon. Patchy smoke is expected after 4 p.m.
Pre-frontal pressure gradients will produce gusty southwesterly surface winds, gusting 35 to 45 mph across southeast Oregon and the Snake River Plain down to the Nevada border Saturday afternoon and evening. Residents should secure outdoor furniture and loose items before the front arrives.
Saturday Night: Cold Front Arrives
The primary cold front will push west to east across the area late Saturday evening, with showers and thunderstorms possible north of a Rome-Ontario-Stanley line into Sunday morning. The best chance for showers and thunderstorms will be focused across Baker County in Oregon and central Idaho north of the Snake River Basin. The Treasure Valley will see mostly cloudy skies Saturday night with winds gusting up to 24 mph as the front pushes through.
Sunday: How Much Cooler Will It Feel?
Sunday will feel dramatically different from Saturday. Here is how Sunday's forecast highs compare to normal for key locations:
| Location | Forecast High Sunday | Normal High | Departure from Normal |
|---|---|---|---|
| Boise (Treasure Valley) | 66°F | 81°F | -15°F |
| Twin Falls | 67°F | 78°F | -11°F |
| McCall | 54°F | 72°F | -18°F |
| Sun Valley (Ketchum) | 65°F | 70°F | -15°F |
Temperatures will plummet roughly 15 to 20 degrees below Saturday's highs. Breezy westerly winds of 10 to 15 mph will make it feel even cooler. Snow levels will drop to 7,000 to 8,000 feet, bringing light snow accumulations to the high mountain peaks. Showers will linger across the northern and eastern mountain zones Sunday morning before tapering off Sunday afternoon.
Travel Weather for the Weekend
Saturday: Excellent travel conditions with sunny skies and warm temperatures. Be aware of gusty southwesterly winds developing Saturday afternoon and evening, particularly along the Snake River Plain and southeast Oregon. High-profile vehicles should use caution. Patchy smoke may reduce visibility in some areas Saturday afternoon.
Saturday Night: Gusty winds and increasing clouds as the cold front pushes through. Winds gusting up to 24 mph in the Treasure Valley. Use caution on mountain passes as showers and thunderstorms develop north of the Snake River Basin.
Sunday: Breezy and significantly cooler with westerly winds of 10 to 15 mph. Mountain passes in central Idaho will see showers and potentially light snow above 7,000 to 8,000 feet Sunday morning. Travelers heading to McCall, Sun Valley, or other mountain destinations should be prepared for wet and potentially snowy conditions on higher elevation roads Sunday morning. Conditions will improve Sunday afternoon as showers taper off.
Sunday Night: Clearing skies and lighter winds will support rapid cooling, with lows near 48 degrees in the Treasure Valley. Patchy valley fog is possible early Monday morning.
Central Idaho Mountains: Showers and High Elevation Snow
The central Idaho mountains will see the most significant weather impacts this weekend. Showers and thunderstorms will develop Saturday night, with the central mountains of western Idaho and eastern Oregon seeing the bulk of the precipitation. Snow levels dropping to 7,000 to 8,000 feet means the highest peaks could see light snow accumulations Saturday night into Sunday morning. Hikers and campers in the backcountry this weekend should be prepared for rapidly changing conditions and have rain and wind gear readily accessible.
Looking Ahead: Warming and Drying Next Week
Clearing skies Sunday night will lead to a cold but beautiful Monday with sunny skies and a high near 70 degrees. A large ridge of high pressure will then rebuild, bringing a steady warming trend through the week. Temperatures will climb from 75 degrees Tuesday to 83 degrees Thursday under sunny skies and dry conditions. A slight chance of showers returns Thursday and Friday as a trough approaches from the west.
Tonight
Mostly clear, with a low around 57. Light wind.
Saturday
Patchy smoke after 4pm. Mostly sunny, with a high near 86. Light and variable wind becoming south 5-10 mph.
Saturday Night
Patchy smoke before 7pm. Mostly cloudy, with a low around 54. South-southeast wind 5-10 mph becoming breezy from the northwest after midnight. Winds could gust as high as 25 mph.
Sunday
Sunny, breezy & much cooler, with a high near 66. West wind 10-15 mph.
Sunday Night
Mostly clear, with a low around 48. Breezy early then diminishing wind.
Monday
Sunny & cooler than normal, with a high near 70.
Monday Night
Clear, with a low around 46.
Tuesday
Sunny, milder and pleasant with a high near 75.
Tuesday Night
Mostly clear, with a low around 48.
Wednesday
Sunny & pleasant, with a high near 77.
Wednesday Night
Mostly clear, with a low around 51.
Thursday
Sunny & warmer with a high near 81.
Thursday Night
A 20 percent chance of showers. Mostly clear, with a low around 55.
Friday
A 20 percent chance of showers. Sunny, with a high near 83.
