FXUS65 KBOI 270914 AFDBOI

Area Forecast Discussion National Weather Service Boise ID 314 AM MDT Sat Jul 27 2024

SHORT TERM
Today through Monday night...Smoky conditions and poor air quality will persist throughout the day due to unchanged surface winds. Similar to yesterday, this will help keep temperatures a few degrees cooler, with the lower valley reaching the upper 80s to low 90s. Moisture will increase this morning as an approaching upper-level low, currently over central California at 3 AM MDT, tracks north- northeast and weakens while moving across the forecast area this evening.
There is ample residual monsoonal moisture, with precipitable water values around the 60th percentile today. However, instability will be limited by significant wildfire smoke. High- resolution models indicate development primarily over the higher terrain this afternoon. Better instability, dynamic support, and moisture are expected further east across south-central Idaho into the central Idaho Mountains, where a few storm clusters may develop. The confidence for thunderstorms today is low (20% chance), as most high-resolution models likely aren’t accounting for smoke, which affects CAPE and temperature forecasts.

Sunday is expected to be dry with light northerly surface winds under a persistent weak westerly flow aloft. The HRRR model shows some improvement in smoke aloft with increased westerly flow; however, this seems unlikely due to the significant number of large fires in Central Oregon. Increased wind may promote slightly better afternoon mixing, but the northerly surface flow is expected to continue bringing smoke from eastern Oregon into the valleys.

Southwesterly flow returns on Monday ahead of the next Pacific trough, but this will not significantly clear the smoke, as smoke from the Park Fire in California will return aloft. The trough and front are expected to reach eastern Oregon late Monday. The main question is whether there will be enough Pacific moisture for thunderstorms to develop late Monday night.
Most recent guidance favors a dry frontal passage, differing from earlier forecasts. For now, a 15% chance of thunderstorms is forecast for Monday night in parts of Southeast Oregon.

LONG TERM
Tuesday through Saturday...A Pacific Northwest trough is expected to bring a cold front through E Oregon and SW Idaho early Tuesday morning. While moisture will be limited, a slight chance (10- 20%) of showers and thunderstorms is forecast along and behind the front for eastern OR and w-central ID Tuesday morning and afternoon. Temperatures will cool a few degrees Tuesday in the wake of the front, and afternoon west and northwest surface winds will become breezy. The trough will quickly exit by Tuesday night, and a strong ridge will strengthen over the Intermountain West. Dry conditions with warming temperatures will return by Wednesday, with temperatures pushing past 100 degrees in the low elevations on Thursday.
Heat will intensify Friday/Saturday with south to southwest flow dominating aloft. Widespread smoke is expected to continue from regional wildfires, with degraded air quality likely.
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