Boise is in for one last stretch of warm, dry autumn weather before a significant cold front arrives this weekend and ushers in cooler temperatures, showers, and mountain snow.
I expect high temperatures reaching the 80s in the lower valleys through Friday — near daily record highs. An upper level ridge is keeping conditions warm and dry through the end of the week.
Overnight lows will remain cool, ranging from the 40s to the lower 50s in the valleys and dropping into the 30s in the mountains.
West winds are expected to increase Friday afternoon, especially south of the Lower Snake Basin, as a cold front approaches from the northwest. The front is forecast to pass through the region early Saturday morning.
A major pattern change arrives Saturday
Saturday high temperatures will be about 20 degrees cooler than Friday's peaks, with highs expected near 66°F. Precipitation will spread into the area Saturday, with the best chances across West-Central and Central Idaho and the Boise Mountains.
Snow levels will fall from northwest to southeast throughout Saturday, allowing for light snow accumulations above 7,500 feet in west-central Idaho by Saturday night.
Cold air from the northwest will continue pushing into the region Sunday, dropping high temperatures an additional 5 to 10 degrees. High elevation snow will persist over the West-Central and Central Idaho mountains through Sunday.
Hurricane moisture could bring significant rainfall next week
Hurricane remnants from the eastern Pacific are expected to carry a significant bout of moisture northeastward through the western United States. The bulk of the precipitation is expected to reach the Northern Rockies by mid-Sunday and continue into Monday, with the western edge of that moisture clipping southwest Idaho.
Forecasters have higher confidence for notable precipitation across the SW Idaho Highlands, Magic Valley, Camas Prairie, and the Central Idaho Mountains. Areas farther west and north face lower chances.
Idaho is forecast to see more precipitation than neighboring Oregon in this system. The coldest air is expected to primarily pass through Oregon, while Idaho remains under milder but moister southerly flow aloft.
The exact path of the moisture remains uncertain. Precipitation is expected to taper by Monday night as both the parent trough and tropical moisture exit the area.
Some forecast guidance indicates a secondary, colder trough could arrive in eastern Oregon and southwest Idaho late Tuesday or Wednesday. Other models suggest a slight blocking pattern that would bring drier, warmer conditions instead.
| Day | Forecast High (°F) | Historical Record High (°F) | Year Record Set |
| Wednesday (Oct 7) | 86° | 86° | 1980 |
| Thursday (Oct 8) | 85° | 88° | 1910 |
| Friday (Oct 9) | 85° | 90° | 2015 |
Tonight
Clear, with a low around 50. Light wind.
Thursday
Sunny, with a high near 85. Light and variable wind.
Thursday Night
Mostly clear, with a low around 52. Light and variable wind.
Friday
Sunny, with a high near 85. Light wind.
Friday Night
Partly cloudy, with a low around 47. Light wind.
Saturday
Partly sunny, breezy & much cooler, with a high near 66.
Saturday Night
A 20 percent chance of showers before midnight. Mostly cloudy, with a low around 39.
Sunday
A 20 percent chance of showers after noon. Partly sunny & unseasonably cool, with a high near 59.
Sunday Night
A 30 percent chance of showers. Mostly cloudy, with a low around 38.
Columbus Day
A 20 percent chance of showers. Patchy fog before 10am. Otherwise, partly sunny, with a high near 59.
Monday Night
A 30 percent chance of showers. Patchy fog. Otherwise, partly cloudy, with a low around 39.
Tuesday
A 30 percent chance of showers. Patchy fog. Otherwise, mostly sunny, with a high near 63.
Tuesday Night
A 20 percent chance of showers. Partly cloudy, with a low around 42.
Wednesday
A 20 percent chance of showers. Patchy fog. Otherwise, mostly sunny, with a high near 62.
