textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Cold front with widespread showers, isolated thunderstorms, and gusty winds, coming in from the west late today and tonight.

- Breezy and cooler Monday, with showers continuing in the north, but becoming sunny in the south.

- Warmer and drier Tuesday through Thursday.

- Windy and cooler with showers Friday.

- Sunny and warmer next weekend.

SHORT TERM /Through Tuesday Night/

Issued 202 AM MDT SUN SEP 6 2026 An upper low is still centered on the OR coast as it has been since Thursday, and like the last two nights a band of showers and isolated thunderstorms has set up from nw MT through the Boise Mountains in ID to north-central NV. As was the case then, tonight's band should weaken overnight with showers ending from south to north before sunrise. But unlike the past two nights, showers have increased in western and central OR, and these should continue as the upper low moves inland today. A surface cold front will take shape in eastern OR this afternoon with a band of showers and thunderstorms developing along and just west of it. The front is forecast to move across the OR/ID border around 5 PM MDT, through the Treasure Valley 5 PM to 8 PM, and Jerome and Twin Falls around 10 PM. In southwest Idaho the front and wind shift will arrive first, then the showers. Showers will decrease as the front continues eastward across the Snake Basin, but frontal winds look stronger east of BOI with gusts 40 to 50 mph and local blowing dust in the Magic Valley. On the other hand, showers will increase in central Idaho along and behind the front this evening, with isolated thunderstorms and locally heavy rain in Valley and Boise Counties. The front will exit our CWA overnight but the upper low and showers will continue in the central Idaho mountains Monday. Snow level will dip only to 8000 feet Monday so snow will not be an issue. Total rainfall today through Monday will be .25 to .50 inch in Valley County/ ID, .10 to .20 inch in other northern areas and in southern mountains, and less than .10 inch in southern valleys. These amounts are less than forecast yesterday. Southern areas will become sunny on Monday with breezy west winds, and all areas will be at least 10 degrees cooler than today. Latest models show a secondary upper low in our northern zones Monday night. This low will maintain clouds in northern zones and breezy west winds in southern zones through Monday night. Tuesday finally looks sunny and warmer in all areas as the secondary low moves out.

LONG TERM /Wednesday through Sunday/

Issued 202 AM MDT SUN SEP 6 2026 Warmer and drier Wednesday and Thursday as weak high pressure aloft rebuilds over the interior western US. Moisture from westward-moving hurricanes in the Pacific subtropics should stay well to our south. The next upper trough is forecast in from BC Thursday night and Friday, which is earlier than forecast yesterday. As the trough comes closer, southwesterly flow aloft may tap into tropical moisture and moisten the cold front now expected in our CWA early Friday. Then after brief cooling Friday, next weekend looks sunny and warmer again as an upper ridge builds over the western states.

AVIATION /12Z Sunday through Monday/

Issued 514 AM MDT SUN SEP 6 2026 Generally VFR. Patchy mountain-valley fog/stratus early morning. Isolated showers in southwest ID early this morning. Numerous showers and scattered thunderstorms in E Oregon this afternoon, shifting into SW Idaho this evening. MVFR in local heavy rain, and gusty outflows with storms. Surface winds: variable up to 10 kt this morning, then SW-NW 10-15 kt with gusts to 30 kt this afternoon/evening, except gusts 35-45 kt and local MVFR in blowing dust from KMUO through KJER and KTWF in the evening. Winds aloft at 10kft MSL: S-SW 20-30 kt.

KBOI...VFR. a 60% chance of showers and thunderstorms this evening. Surface winds: variable or light SE this morning, becoming NW 10-15 kt after 21Z, then NW 15-30 kt this evening, decreasing after 07/04Z.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.