The prolonged stretch of above-normal heat across the Treasure Valley and central Idaho mountains is finally coming to an end. A significant pattern change will arrive Friday, dropping temperatures 10 to 15 degrees and bringing widespread shower activity before a cooler and more fall-like pattern takes hold through the weekend and into next week.
Thursday: Last Day of Intense Heat with Morning Shower Chances
Thursday will be the final day of the prolonged heat event, with Treasure Valley highs near 95 degrees. For context, Boise's average high for late August is around 89 degrees, meaning Thursday will still run about 6 degrees above normal. Isolated morning shower activity is possible Thursday before 9 a.m., though impacts will be limited. Afternoon thunderstorm chances will continue near the Nevada border and into the central Idaho mountains Thursday afternoon, with gusty erratic outflow winds up to 40 mph possible with stronger storms.
Increasing flow aloft ahead of a strengthening upper trough will bring elevated to critical fire weather conditions to eastern Oregon and eventually into western and central Idaho Thursday. Anyone in these areas should be aware of the elevated fire danger.
Friday: Major Pattern Change Brings Widespread Showers and Significant Cooling
Friday marks a dramatic shift in the weather pattern. Moisture values will increase significantly, exceeding the 90th percentile, promoting scattered to widespread shower development. Ensemble guidance supports a focused band of shower development spanning from near the Nevada-Oregon-Idaho border northeastward across southwest Idaho Friday. Rainfall amounts are likely to remain under a quarter inch in most locations, but the widespread coverage will be a welcome change after the prolonged dry and hot stretch.
Temperatures will cool significantly Friday, dropping 10 to 15 degrees from Thursday's highs to near 84 degrees in the Treasure Valley. This will be the most dramatic single-day temperature drop of the summer season and will finally bring temperatures back to near late-summer normals.
Weekend: Cooler and More Comfortable Conditions
Saturday will bring a 20 to 50 percent chance of showers across much of southwest Idaho, including Baker County in Oregon, as the upper trough axis remains positioned to the west. Breezy westerly winds behind Friday's cold front will bring gusts of 20 to 30 mph Saturday afternoon. Temperatures will be near normal Saturday with highs near 85 degrees.
Sunday will be the coolest day of the period, with temperatures dropping 5 to 10 degrees below normal and lower elevations seeing highs only in the upper 70s. Gusty winds will continue across the Snake River Plain Sunday as drier and cooler air moves in on the backside of the trough. This will make for excellent outdoor conditions after weeks of oppressive heat.
Outdoor and Travel Planning
- Thursday: Hot conditions with highs near 95 degrees. Stay hydrated and limit outdoor activities to the early morning hours. Be aware of afternoon thunderstorm chances in the mountains and Magic Valley with gusty outflow winds possible.
- Friday: Significant change arrives with widespread showers and temperatures dropping to the mid-80s. A great day to stay flexible with outdoor plans.
- Weekend: Near to below-normal temperatures in the mid to upper 80s Saturday and upper 70s Sunday will make for much more comfortable outdoor conditions. Some shower chances Saturday, with gusty winds both days.
- Next Week: Brief ridging Monday will bring dry conditions and a quick return to above-normal temperatures near 86 degrees. Another trough Tuesday and Wednesday will bring a chance of showers and thunderstorms across west-central and south-central Idaho, with temperatures trending toward normal to slightly below normal.
Tonight
Mostly cloudy, with a low around 69. Calm wind becoming east southeast 5 to 7 mph after midnight.
Thursday
A 30 percent chance of showers, mainly before 9am. Mostly sunny and hot, with a high near 95. Calm wind becoming west southwest 5 to 7 mph in the afternoon.
Thursday Night
Increasing clouds, with a low around 65. West wind around 6 mph becoming calm in the evening.
Friday
A 30 percent chance of showers after noon. Mostly cloudy, with a high near 84. Calm wind becoming south southeast 5 to 8 mph in the afternoon.
Friday Night
A 40 percent chance of showers. Mostly cloudy, with a low around 61.
Saturday
A 20 percent chance of showers. Mostly sunny, with a high near 85.
Saturday Night
A 20 percent chance of showers before midnight. Partly cloudy, with a low around 54.
Sunday
Sunny, with a high near 78.
Sunday Night
Mostly clear, with a low around 54.
Monday
A 20 percent chance of showers. Sunny, with a high near 86.
Monday Night
Partly cloudy, with a low around 57.
Tuesday
Mostly sunny, with a high near 86.
