textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Scattered thunderstorms this afternoon and evening could produce strong outflow winds, small hail and brief heavy rain. - Unseasonably cold air arrives Sunday. This will bring lowering snow levels with measurable snowfall expected above 6500 feet on Sunday.

- Temperatures remaining 15 to 20 Sunday degrees below normal on Monday.

SHORT TERM /Through Monday Night/

Issued 232 PM MDT SAT JUN 27 2026 An active short term period continues as an upper level low moves across the area this afternoon and into Montana tonight. For the remainder of this afternoon and through this evening, the primary focus will be on thunderstorm development. These storms are expected to bring heavy rain, small hail, and gusty winds, with the most widespread activity centered over southwest Idaho. Given the high moisture content and slow storm motion, the strongest convective cells could produce enough intense rainfall to cause localized flooding. A Flash Flood Watch remains in effect through this evening for the Wapiti burn scar. Anyone near the burn area or within the central Idaho mountains should remain alert, as rock or mud slides are a distinct possibility with any heavy downpours.

The upper level low is projected to move eastward into Montana tonight. As it does, wrap around precipitation and significantly colder air will pull into central Idaho from the north and backside of the system. This setup will keep a steady threat of showers over the Central Idaho Mountains through Sunday. With the influx of cold air, snow levels will drop rapidly, bringing measurable snowfall to areas above 6500 feet on Sunday. Travel over higher mountain passes could become slick and slushy. Precipitation will gradually taper off Sunday night as the main low pulls further away.

The region remains under a cool northerly flow on Monday as the upper low sits to our east. This pattern will keep temperatures well below seasonal normals, running about 15 to 18 degrees colder than typical late June averages. A lingering 20% chance of precipitation will persist across the west central mountains through Monday afternoon before dry air takes over completely.

LONG TERM /Tuesday through Saturday/

Issued 232 PM MDT SAT JUN 27 2026 Ensembles remain in good agreement with long wave troughing remaining in place into the holiday weekend. The trough axis migrates just to the east of the area should drop the available moisture which will reduce the potential for precipitation mid week. By Thursday, the next low pressure system from Alaska looks to reach the Pacific Northwest coast. This will shift the flow to the southwest and increase moisture aloft. Most guidance shows the trough and cold front moving inland on Friday which will increase the chances for thunderstorms across the area. Temperatures will remain below normal through the period with the warmest day looking like Thursday at about 5 degrees below normal.

AVIATION /00Z Sunday through Monday/

Issued 632 PM MDT SAT JUN 27 2026

Generally VFR. Isolated showers/thunderstorms this eve, capable of brief heavy rain, small hail, and gusts to 25-35 kt. Thunder tapering off around sunset, with showers lingering overnight mainly over the W-Central ID Mtns. Local MVFR ceilings in showers through Sunday, and mtns obscured. Snow levels lowering to 6500-7500 ft MSL Sunday AM. Surface winds: W-NW 10-20 kt with gusts to 20-30 kt through sunset, then SW-NW 5-15 kt overnight. Winds aloft at 10kft MSL: W-NW 15-30 kt.

KBOI...Generally VFR. Isolated showers/thunderstorms in Treasure Valley through tonight, with 25% chance of lightning impacting terminal through sunset. Brief MVFR conditions possible in showers/tstorms. Storms also capable of heavy rain, small hail, and 30 kt outflows. Ceilings lowering to low VFR or brief MVFR Sunday AM. Surface winds: NW 5-15 kt.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Flash Flood Watch for Wapiti Burn Scar until 9 PM MDT this evening for IDZ013. OR...None.