textproduct: Boise
This forecast discussion was created in the public domain by the National Weather Service. It can be found in its original form here.
LONG TERM...Wednesday through Sunday
High pressure will continue to build over the region through the work week, with air stagnation concerns from a persistent surface inversion expected through at least Thursday. Temperatures will remain warm during the daytime and likely above freezing for higher elevations (5000-7000 feet MSL) above the inversion. Cold pools with below normal temperatures will linger in lower elevation valleys, with the potential for low clouds and fog to develop each morning, primarily in sheltered mountain valleys.
Relief from the stagnant conditions could come as early as Friday with a dry cold frontal passage to our east potentially bringing breezy winds and cooler air into the valley. The big question mark in this forecast outcome is how far west the cold front/upper level trough will track, with the bulk of the ECMWF ensembles and EC AI solution keeping the frontal passage further east. This would keep the stagnant conditions in place over the area through the weekend. Regardless, precipitation and a significant change in weather is not anticipated in the long term period.
AVIATION
VFR under high clouds. Areas of fog/low stratus in sheltered valleys will mix out by late morning, MVFR/LIFR with mtn obscuration in fog/low stratus. Surface winds: Variable up to 10 kt except NE 10-20 kt with gusts up to 30 kt near KJER and portions of the Snake Basin. Winds aloft at 10kft MSL: Variable 5-20 kt.
KBOI...VFR. Surface winds: SE 5-10 kt.
AIR STAGNATION
High pressure will remain centered over the region through the end of the week. A light east to southeast breeze will continue today, but lighter winds will develop the rest of the week under valley temperature inversions. Additionally, mixing heights are expected to remain below 1500 feet AGL for an extended period. These conditions will severely limit ventilation, leading to the accumulation of pollutants in valley locations. The Air Stagnation Advisory is currently in effect until 5 am MST Friday for all valley zones in southeast Oregon and southwest Idaho. Long range models suggest these conditions may persist beyond Friday, although confidence is lower.
BOI WATCHES/WARNINGS/ADVISORIES
ID...Air Stagnation Advisory until 5 AM MST Friday IDZ011>014-016-028-033. OR...Air Stagnation Advisory until 5 AM MST /4 AM PST/ Friday ORZ061>064.
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