One More Warm Day Before the Weather Changes
Enjoy Wednesday's warmth because a significant change in our weather arrives later this week.
Wednesday stays mainly dry and unseasonably warm across the Treasure Valley, with Boise climbing to around 76 degrees. Clouds will gradually increase as moisture begins moving north ahead of a Pacific storm system.
A few showers and thunderstorms may begin developing Wednesday afternoon and evening, but the main event arrives Thursday.
The National Weather Service Boise Area Forecast Discussion says the chance of thunderstorms is around 10-20% Wednesday afternoon and evening, increasing to around 30% Thursday afternoon and evening as the upper-level storm and cold front arrive.
Scott Dorval's video forecast
Thursday Brings Widespread Rain
Thursday looks like the wettest day of the week, with rain becoming widespread across Southwest Idaho and continuing through Thursday night.
The latest forecast guidance has also become wetter. The National Weather Service Boise Area Forecast Discussion increased expected precipitation by roughly 15% from the previous model cycle, forecasting 0.20 to 0.40 inches in the Treasure and Magic valleys and 0.40 to 0.75 inches at higher elevations Thursday and Thursday night.
Southeast Oregon should generally receive less rain because it will remain on the western side of the storm. Oregon valleys are forecast to see roughly 0.15 to 0.25 inches, with amounts up to 0.40 inches at higher elevations or closer to the Idaho border. [forecast.weather.gov]
How Much Rain Could We Get?
| Location | Expected Rainfall* |
|---|---|
| Boise | 0.35–0.55" |
| Ontario, OR | 0.15–0.25" |
| McCall | 0.40–0.75" |
| Cascade | 0.40–0.75" |
| Idaho City | 0.40–0.75" |
| Mountain Home | 0.20–0.40" |
| Twin Falls | 0.25–0.50" |
| Ketchum | 0.60–0.90" |
For Boise, the point forecast calls for 0.10–0.25 inches Thursday followed by another 0.25–0.50 inches Thursday night, with locally higher amounts possible around thunderstorms.
All Rain at First, Then Mountain Snow Levels Fall
This initially looks like a rain event even in the mountains.
Snow levels will remain above 9,000 feet Thursday, meaning precipitation should fall primarily as rain. As much colder air arrives Friday, however, snow levels fall to around 6,000–7,000 feet by Friday afternoon. Higher passes and ridgelines could see a dusting, while the highest summits could approach an inch before precipitation diminishes early Saturday.
Windy and Much Colder Friday
The cold front sweeps through late Thursday night, shifting winds to the northwest and bringing a noticeable temperature drop.
Friday's high in Boise is forecast to reach only around 57 degrees, nearly 20 degrees colder than Wednesday's forecast high. Northwest winds could gust 30–45 mph across the region Friday, while showers gradually decrease.
Friday night turns chilly, with Boise dropping to around 35 degrees.
A Drier Weekend Returns
The storm moves away heading into the weekend as high pressure begins building along the West Coast.
Saturday should turn mostly sunny after some areas of morning fog, with Boise reaching around 59 degrees. Sunday warms into the mid-60s with mostly sunny conditions.
Forecast confidence decreases heading into early next week. Longer-range models disagree on whether another low-pressure system moves inland or high pressure remains over the Intermountain West. For now, the forecast favors a modest warming and drying trend through Monday, with only a slight precipitation chance in the West Central Mountains.
Tonight
Increasing clouds, with a low around 49. Light wind.
Wednesday
Partly sunny through mid morning, then becoming sunny, with a high near 76. Light wind.
Wednesday Night
A chance of showers and thunderstorms. Mostly cloudy, with a low around 51. Light wind. Chance of precipitation is 30%.
Thursday
Showers, with thunderstorms also possible after noon. High near 71. Light wind. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
Thursday Night
Showers and possibly a thunderstorm. Patchy fog between 11pm and midnight. Low around 45. Calm wind becoming west 5-10 mph after midnight. Chance of precipitation is 90%. New precipitation amounts between a quarter and half of an inch possible.
Friday
A 50 percent chance of showers before noon. Partly sunny, breezy & much cooler, with a high near 57.
Friday Night
Mostly clear with widespread frost, with a low around 35.
Saturday
Patchy fog between 8am and 9am. Otherwise, sunny & cool, with a high near 59.
Saturday Night
Mostly clear, with a low around 39.
Sunday
Mostly sunny & milder, with a high near 64.
Sunday Night
Partly cloudy, with a low around 41.
Monday
Mostly sunny, with a high near 64.
Monday Night
Partly cloudy, with a low around 40.
Tuesday
Mostly sunny, with a high near 64.
