The Treasure Valley will enjoy one more warm and sunny day Thursday before a powerful cold front sweeps through Saturday evening, bringing gusty winds, showers, and a dramatic temperature drop that will make Sunday feel like a completely different season.
Heating up Thursday before a big cool down for Sunday in Scott Dorval's video forecast
Thursday: Last Warm Day Before the Pattern Changes
Thursday will be the warmest day of the week, with the Treasure Valley reaching a high near 88 degrees under sunny skies and light winds. This is about 6 degrees above the normal high for mid-September in Boise, which typically sits around 82 degrees. It will be a spectacular day to be outdoors, with low humidity, clear skies, and comfortable conditions.
A dry cold front will push through the area Thursday evening, bringing gusty westerly winds and some high clouds. Friday will be cooler but still pleasant at 80 degrees, with breezy post-frontal winds lingering over high terrain areas through the afternoon.
Saturday: Warm Before the Storm
Saturday will start warm and mostly sunny with a high near 79 degrees as southwest flow ahead of the incoming upper low keeps temperatures above normal. However, conditions will change rapidly Saturday afternoon and evening as the upper low quickly moves into the area from off the Oregon coast.
The Big Event: Powerful Cold Front Saturday Evening
The most significant weather event of the week arrives late Saturday as a powerful cold front sweeps through the region. Gusty winds will develop across the entire southern half of the region from southeast Oregon near the Nevada border to the lower Snake River Plain. Expect wind gusts to 40 mph in open areas.
Sunday: Dramatically Cooler and Breezy
Sunday will feel like a completely different season compared to Thursday's 88-degree warmth. Temperatures will drop to a high near 65 degrees, running about 17 degrees below Thursday's peak and about 17 degrees below the normal high for this date. A 30 percent chance of showers will linger through the morning as moisture wraps around the northern and western flanks of the eastward-moving upper low. Snow levels will drop to the 7,000 to 8,000-foot range, favoring some light snow showers over the highest mountain peaks.
By late Sunday, western zones will clear, and Sunday night will be clear and cold area-wide with lows near 46 degrees in the Treasure Valley.
Recreation Forecast: Treasure Valley and Central Idaho Mountains
Wednesday and Thursday: The best outdoor days of the week. Sunny skies, temperatures in the low to upper 80s, and light winds make these ideal days for hiking in the Boise Foothills, cycling the Greenbelt, or any outdoor activity. Thursday will be particularly spectacular.
Friday: Still a very good outdoor day with sunny skies and a high near 80 degrees. Breezy conditions over high terrain areas in the afternoon.
Saturday morning and early afternoon: Good conditions for outdoor activities before the front arrives. Mostly sunny with a high near 79 degrees. Plan to be off exposed ridges and mountain summits by early afternoon as conditions will deteriorate rapidly Saturday evening.
Central Idaho Mountains this weekend: The mountains will see the most significant weather impacts this weekend. Showers and thunderstorms will develop Saturday evening, 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 Saturday night into Sunday. Hikers and campers in the backcountry this weekend should be prepared for rapidly changing conditions and have rain and wind gear readily accessible. Sunday will bring continued shower chances and gusty conditions before clearing late in the day.
McCall and surrounding areas: The combination of gusty winds Saturday night and shower chances makes Saturday evening through Sunday morning the most challenging period for outdoor activities. Plan mountain trips for Thursday or Friday for the best conditions.
Looking Ahead: Warming and Drying Early Next Week
Sunday night will be clear and cold, with valley fog possible early Monday morning. Monday will then bring sunny skies and a high near 68 degrees before temperatures climb to 73 degrees Tuesday and 75 degrees Wednesday under dry and warm conditions. This pattern of alternating warm and cool periods is very typical of September in the Treasure Valley and signals the gradual but steady transition toward fall.
Tonight
Clear, with a low around 54. Northwest wind 5 to 7 mph becoming light and variable.
Thursday
Sunny, with a high near 88. Calm wind becoming west northwest 5 to 7 mph in the afternoon.
Thursday Night
Partly cloudy, with a low around 57. North northwest wind 5 to 8 mph becoming calm after midnight.
Friday
Sunny, with a high near 80. Calm wind becoming west northwest 5 to 7 mph in the morning.
Friday Night
Mostly clear, with a low around 55. Northwest wind around 6 mph, becoming light and variable in the evening.
Saturday
Mostly sunny, with a high near 79. Gusty evening wind
Saturday Night
A chance of showers and thunderstorms. Mostly cloudy, with a low around 49. Chance of precipitation is 50%. Gusty NW wind
Sunday
A 30 percent chance of showers. Partly sunny & breezy, with a high near 65.
Sunday Night
Mostly clear, with a low around 46.
Monday
Patchy fog between 8am and 9am. Otherwise, sunny, with a high near 68.
Monday Night
Mostly clear, with a low around 48.
Tuesday
Sunny, with a high near 73.
Tuesday Night
Mostly clear, with a low around 50.
Wednesday
Sunny, with a high near 75.
