Sunrise 6:13 AM   Sunset 9:09 PM Moonrise 4:29 PM   Moonset 3:21 AM

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FXUS65 KBOI 191550 AFDBOI

Area Forecast Discussion National Weather Service Boise ID 950 AM MDT Sun May 19 2024

DISCUSSION
Winds will remain gusty today behind last night's cold frontal passage. The pressure gradient and winds aloft will support widespread gusts of 20-30 mph while windier spots across the middle Snake Plain will see gusts to 40 mph through this evening. The mountains of Baker County and w-central Idaho are in line for isolated showers, mostly developing this afternoon with the daytime heating and instability. High temperatures today will be about 10-15 degrees cooler than yesterday, or about 10 degrees below normal. Current forecast is on track for today.

AVIATION
VFR. Mid clouds and isolated showers in mountains of northeast Oregon and w-central Idaho which could reach KBKE and KMYL this afternoon. Mountains obscured in showers. Snow levels 5-6kft MSL after 18Z. Surface winds: generally NW to N 10-20 kt, gusts to 20-25 kt. In Magic Valley, W 15-25 kt with gusts to 30-35 kt, decreasing to 10-15 kt with gusts to 20-25 kt around Sun/16Z. Winds aloft at 10k ft MSL: NW 10-30 kt.

KBOI...VFR. Gusty NW winds through sunset. Prescribed fires in the Boise foothills will continue to bring haze and reduced visibility aloft.

PREV DISCUSSION
SHORT TERM
Today through Tuesday night
An upper-level trough will remain over the region through Monday, continuing to bring colder temperatures and breezy conditions. A cold front is moving east across south-central Idaho this morning, generating wind gusts up to 40 MPH. Winds will weaken later this morning but will return this afternoon with gusts up to 35 MPH, particularly in the Western Snake River Plain, as the upper- level trough advances over the forecast area. There is sufficient moisture and instability ahead of the trough axis to support a 30% chance of showers and thunderstorms in the West Central and Boise Mountains of Idaho. Temperatures are expected to drop to approximately 10 degrees below normal.

The upper-level trough will persist across the entire forecast area on Monday. Most model guidance indicates a weak upper-level low forming over south-central Idaho by Monday afternoon. This increased dynamic support, coupled with weak instability and moisture, appears adequate to support showers and thunderstorms in the afternoon and evening. The Boise Mountains have the highest chance for precipitation, with probabilities between 30% and 50%. Additionally, several high-resolution models show convective activity moving from the mountains into the Upper Treasure Valley and Western Magic Valley by Monday afternoon.
Breezy northwest winds will continue, maintaining below-normal temperatures across the area through Monday.

A transient ridge is expected to follow on Tuesday as the region remains between systems. Temperatures will rise approximately 6 degrees above Monday’s highs but will still be about 4 degrees below normal. A much stronger low-pressure system is forecast to reach the Pacific Northwest late Tuesday, pushing a cold front into the forecast area. Although model timing of the frontal passage varies, the majority agree on precipitation along the front late Tuesday night across southeast Oregon.

LONG TERM
Wednesday through Sunday
A relatively cold, vigorous low from western Canada will arrive over east Oregon and southwest Idaho by early Wednesday. This low will introduce precipitation chances (50-80%) across the area Wednesday into Thursday, along with breezy winds and temperatures up to 10-15 degrees below normal. Snow levels will begin around 6500-7500 ft MSL early Wednesday and lower to 4500-5500 ft MSL by early Thursday. As a result, light snow accumulations down to 5000 ft are possible, along with several inches in the mountains above 7000 ft. A slight chance (15%) of thunderstorms are also forecast for Wednesday afternoon with the initial cold front and precipitation. Conditions will trend drier throughout Thursday as the trough exits toward the east and northerly flow establishes over the PacNW. Thereafter, slightly warmer temperatures are anticipated Friday with the return of brief ridging. Models have come into better agreement with bringing in the next low pressure system Saturday into Sunday, supporting a chance (15-30%) of showers across the area. Models diverge on how far south this trough will progress, as well as how quickly the trough will exit the region. Therefore, the amount of temperature, wind, and shower impact to the forecast area is still uncertain.

BOI WATCHES/WARNINGS/ADVISORIES
ID...None.
OR...None.

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