The Treasure Valley and central Idaho mountains will see continued warm temperatures and daily thunderstorm chances through Thursday before a significant pattern change arrives Friday, bringing a cold front, remnant tropical moisture from Tropical Storm Iselle, and the potential for severe thunderstorms with heavy rain.
Sizzling heat gives way to weekend cooling in Scott Dorval's video forecast
Wednesday and Thursday: Heat Continues with Thunderstorm Chances
Temperatures will remain well above normal Wednesday and Thursday, with the Treasure Valley seeing highs near 97 degrees Wednesday and 95 degrees Thursday. For context, Boise's average high for late August is around 89 degrees, meaning these temperatures will run about 6 to 8 degrees above normal.
Isolated afternoon thunderstorms will be possible near the Nevada border into the western Magic Valley both Wednesday and Thursday afternoons, with strong gusty winds being the primary threat. The central Idaho mountains will also see isolated thunderstorm chances each afternoon. Anyone planning outdoor activities in the mountains or Magic Valley area Wednesday and Thursday should be prepared for rapidly changing weather conditions in the afternoon hours.
By Thursday, increasing southwest flow aloft associated with a strengthening trough will bring gusty winds to southeast Oregon and far southwest Idaho. Combined with low relative humidity and warm temperatures, this will create an elevated wind-driven fire weather threat across these areas. Outdoor recreationists and travelers in these areas should be aware of the elevated fire danger Thursday afternoon.
Friday: Cold Front and Tropical Moisture Bring Severe Storm Potential
The most significant weather event of the week arrives Friday as a cold front drops temperatures back to near normal. What makes this system particularly noteworthy is the remnant moisture from Tropical Storm Iselle, which will be transported over the area in southwesterly flow aloft ahead of the cold front.
Moisture values across southwest Idaho are forecast to increase to around the 95th percentile of climatology, with the highest values near the Magic Valley and eastward. This abundant moisture, combined with the approaching cold front, will create favorable conditions for the development of showers and thunderstorms Friday afternoon, mainly in southwest Idaho. With such high moisture values, heavy rain will be a significant hazard with any storms that develop, and flash flood risks will need to be monitored closely, especially near burn scars and steep terrain.
Some of these storms may be severe. Anyone with outdoor or travel plans in southwest Idaho Friday afternoon should monitor conditions closely and have a plan to seek shelter quickly if storms develop.
Weekend: Cooler and Drier Conditions Return
The cold front and associated upper trough will quickly push the moisture off to the east Saturday, bringing generally dry conditions for the weekend. Temperatures will drop to near or below normal, with highs near 87 degrees Saturday, 85 degrees Sunday, and 88 degrees Monday. This will make for a much more comfortable weekend for outdoor activities compared to the heat earlier in the week.
Looking Ahead: Fall-Like Pattern Emerging
The extended outlook is showing a notable shift toward a more fall-like pattern, with above-normal precipitation and below-normal temperatures favored beyond the long-term period. Another trough digging down the British Columbia coast Monday and Tuesday will bring a slight chance of precipitation across higher terrain of southwest Idaho. This transition pattern represents a significant shift from the hot and dry summer conditions that have dominated the region.
Outdoor and Travel Planning
- Wednesday and Thursday: Hot conditions with highs near 95 to 97 degrees. Stay hydrated and limit outdoor activities to the early morning hours. Be aware of afternoon thunderstorm chances in the mountains and Magic Valley.
- Friday: Significant storm threat with potential for severe thunderstorms and heavy rain in southwest Idaho. Avoid outdoor activities Friday afternoon if possible and monitor conditions closely.
- Weekend: Excellent conditions for outdoor activities with near-normal temperatures in the mid to upper 80s and mostly dry conditions.
Tonight
Cloudy, then gradually becoming partly cloudy, with a low around 67. Light wind.
Wednesday
Mostly sunny and hot, with a high near 97. Breezy in the morning, then light wind.
Wednesday Night
Partly cloudy, with a low around 67. Light wind.
Thursday
Mostly sunny and hot, with a high near 95. Light wind.
Thursday Night
Partly cloudy, with a low around 64. West wind 5 to 7 mph becoming calm after midnight.
Friday
Partly sunny, with a high near 89.
Friday Night
A 20 percent chance of showers before midnight. Mostly cloudy, with a low around 61.
Saturday
Sunny, with a high near 87.
Saturday Night
Mostly clear, with a low around 56.
Sunday
Sunny, with a high near 85.
Sunday Night
Mostly clear, with a low around 56.
Monday
Sunny, with a high near 88.
Monday Night
Partly cloudy, with a low around 59.
Tuesday
Mostly sunny, with a high near 86.
