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…