textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Intermittent showers and embedded thunderstorms across much of southeast Oregon and west-central Idaho Wednesday night through Friday with significant rainfall totals possible.

- Much cooler this week, with highs 10-20 degrees below normal by Thursday with periods of gusty winds.

- Cooler than normal weather anticipated late this weekend into early next week.

SHORT TERM /Through Saturday Night/

Issued 225 PM MDT WED SEP 2 2026 The large upper low is continuing to steer into the northwest region, continuing a strong southwest flow aloft and sending a plume of Pacific moisture into our area. A band of stratiform rain showers is moving towards our area from off the northwest coast this afternoon, and expected to bring widespread precipitation over the area this evening through most of Thursday. Latest satellite imagery indicates some ongoing clearing and cumulus buildups ahead of the precip front, favoring some embedded isolated thunderstorms over eastern OR and the central ID mountains this evening through late tonight. These thunderstorms will be capable of localized heavy rain.

Periods of rain will continue in varied coverage Thursday into Friday as the parent low remains positioned over the Pacific Northwest coast. All areas should see at least a tenth to a half inch from today through Friday except for the Western Magic Valley and Camas Prairie, where lesser amounts will fall. Mountains should see beneficial rainfall with 1.0 to 1.5 inch through Friday evening. Embedded thunderstorms, capable of producing locally heavier amounts, remain possible in the afternoon/evening Thursday and Friday and could cause some localized flash flooding issues for the recent burn scars noted in the Flash Flood Watch. Lowering heights and cool onshore flow will keep temperatures well below normal through Friday. Southeast Oregon and the West Central Mountains of Idaho will see record to near record low max temperatures Thursday and Friday.

LONG TERM /Sunday through Thursday/

Issued 225 PM MDT WED SEP 2 2026 Long-range guidance continues to favor the large upper low hanging over the northwest coast region on Saturday. This pattern will keep our area under a southwest flow that will warm temperatures back up to near-normal. Drier conditions are expected Saturday except for weak showers over high terrain areas of central ID and eastern OR. The upper level low will begin steering east over our area on Sunday, while capturing abundant Pacific moisture from the lower southwest. This pattern shift will bring heightened chances for heavy rainfall over south-central ID late Sunday and through most of Monday. Snow levels may lower enough to bring light snow or mixed precipitation to the highest peaks.

The pattern will continue cooler than normal temperatures through early next week. By Tuesday and Wednesday, ensemble clusters favor a transition to drier conditions and a subtle warming trend as an upper level ridge attempts to build inland from the Pacific coast. Temperatures throughout the long term period will remain generally near or slightly below seasonal averages.

AVIATION /06Z Thursday through Friday/

Issued 1207 AM MDT THU SEP 3 2026 Numerous rain showers through Thursday, becoming widespread Thu evening. MVFR/IFR conditions and mountain obscuration in heavier precip. A 15% chance of embedded thunderstorms in E Oregon and w- central ID through Thursday PM. Snow levels lowering to 7500 ft MSL in E Oregon Thursday night. Surface winds: variable 5-15 kt, then SE- SW 5-15 kt with gusts around 20-25 kt by late morning. Winds aloft at 10kft MSL: S-SW 15-30 kt.

KBOI...Generally VFR. Light rain overnight with a 10% chance of MVFR ceilings. Transitioning to periodic showers after Thu/11Z. Then, continuous rain Thursday evening with a 20% chance of MVFR. Surface winds: NW-NE 5-15 kt, transitioning back to E-SE 5-15 kt after Thu/11Z.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Flash Flood Watch from this afternoon through Friday evening for IDZ011. Flash Flood Watch through Friday evening for IDZ013. OR...Flash Flood Watch from this afternoon through Friday evening for ORZ061>063.