The Treasure Valley will remain under dangerous heat through Sunday before a gradual cooling trend brings temperatures down through the coming week. Wildfire smoke will persist through at least Monday, and isolated late-day thunderstorms will develop near the Idaho-Nevada border Saturday and Sunday.
How Hot Will It Get? Forecast vs. Records
Saturday and Sunday will remain very hot, though not as hot as Friday. Here is how the weekend forecast compares to historical records for Boise and Twin Falls:
| Location | Record High Aug 8 | Record High Aug 9 | Forecast Saturday Aug 8 | Forecast Sunday Aug 9 |
|---|---|---|---|---|
| Boise | 107°F (1990) | 106°F (2018) | 101°F | 98°F |
| Twin Falls | 105°F (1961) | 104°F (1961) | ~101°F | ~98°F |
Heat Advisory: Dangerous Conditions Continue
The upper-level high over the Great Basin will gradually weaken through the weekend, bringing Saturday about 1 to 3 degrees cooler than Friday and Sunday another 2 to 4 degrees cooler. However, conditions will remain dangerously hot with highs near 101 degrees Saturday and 98 degrees Sunday. Overnight lows will change little, staying in the mid-60s and providing only limited relief.
Heat is the leading weather-related killer in the United States. Residents should:
- Stay hydrated by drinking water frequently, even if you don't feel thirsty
- Limit strenuous outdoor activities to the early morning hours
- Use air conditioning or visit a cooling center during the hottest parts of the day
- Never leave children, elderly individuals, or pets in parked vehicles
- Check on vulnerable neighbors, elderly family members, and those without air conditioning
Wildfire Smoke and Air Quality
Wildfire smoke will continue to impact the Treasure Valley and central Idaho mountains through at least Monday. The latest smoke models show little if any improvement through the weekend, with the worst conditions continuing in eastern Oregon. Smoke will be most concentrated during the overnight and early morning hours before afternoon mixing provides brief improvements.
The Idaho Department of Environmental Quality and AirNow.gov provide real-time air quality information. Residents with respiratory conditions, the elderly, children, and others sensitive to smoke should limit outdoor activities and keep windows and doors closed.
Weekend Outdoor Recreation: Plan Carefully
For those planning outdoor activities this weekend, conditions will remain extremely challenging. Afternoon winds will be breezy through Sunday, with gusts up to 20 mph Saturday night. Combined with temperatures near or above 100 degrees, very low relative humidity, and wildfire smoke, these conditions will create elevated fire weather concerns.
If you must be outdoors this weekend, plan activities for the early morning hours before temperatures peak. Bring plenty of water, wear sun protection, and know the signs of heat exhaustion and heat stroke. Be aware of fire restrictions currently in place across the region.
Isolated late-day thunderstorms will develop near the Idaho-Nevada border Saturday and Sunday, mainly in eastern Owyhee and southern Twin Falls counties. These storms will be high-based with strong downdrafts and gusty outflow winds but little rain. Lightning on dry fuels will be the primary concern with these storms.
Central Idaho Mountains
The central Idaho mountains will also experience dangerous heat through the weekend, with temperatures running well above normal. Widespread smoke impacts will affect the mountains as well. Hikers and campers should be aware of fire restrictions and have an evacuation plan in case of new fire starts. The breezy afternoon winds through Sunday will create elevated fire weather conditions across the mountains.
Gradual Cooling Next Week
A welcome cooling trend will develop through the coming week as the persistent upper-level ridge over the Great Basin slowly weakens and retreats southward. Temperatures will drop from 95 degrees Monday to the low 90s by Wednesday and upper 80s by Friday. A low-amplitude trough will develop Wednesday, bringing a slight chance of afternoon thunderstorms near the Nevada-Idaho border Wednesday and Thursday as monsoon moisture returns northward.
Tonight
Areas of smoke. Mostly clear, with a low around 66. West northwest wind 5 to 7 mph becoming calm in the evening.
Saturday
Areas of smoke. Sunny and hot, with a high near 101. Calm wind becoming northwest 5 to 9 mph in the afternoon.
Saturday Night
Patchy smoke. Mostly clear, with a low around 64. Northwest wind 5 to 9 mph becoming calm in the evening. Winds could gust as high as 20 mph.
Sunday
Patchy smoke. Sunny and hot, with a high near 98. Calm wind becoming west northwest 5 to 7 mph in the afternoon.
Sunday Night
Patchy smoke before 3am. Mostly clear, with a low around 62. Northwest wind 5 to 8 mph becoming calm in the evening.
Monday
Sunny and hot, with a high near 95.
Monday Night
Mostly clear, with a low around 62.
Tuesday
Sunny and hot, with a high near 96.
Tuesday Night
Mostly clear, with a low around 63.
Wednesday
Sunny and hot, with a high near 93.
Wednesday Night
Mostly clear, with a low around 63.
Thursday
Sunny and hot, with a high near 91.
Thursday Night
Mostly clear, with a low around 62.
Friday
Mostly sunny and hot, with a high near 90.
