textproduct: Boise

LONG TERM...Tuesday through Saturday

More of the same through the long term, with high pressure and stagnant conditions dominating through the extended. Come Thursday, guidance is hinting at a shortwave swinging northeast of our area. While no precip is expected (better forcing remain northeast of our area), a more westerly track could work to increase transport winds to help mix valley inversions and bring cooler temperatures into our area. However, out of the Grand Ensemble, only 21% of members favor a more westerly track (mostly out of the GFS Suite). The EC-AI, EC, and GFS- AI keep it east which would do little to help mix out our valleys. Beyond Friday, the blocking pattern sets back in the high pressure setting up over the Pacific Northwest, maintaining the dry and stagnant conditions.

AVIATION

VFR under high clouds. Areas of fog/low stratus will develop in sheltered valleys overnight, MVFR/LIFR with mtn obscuration in fog/low stratus. Surface winds: Variable up to 10 kt. Locally higher (gusts up to 20 kt) near KJER and portions of the Snake Basin overnight. Winds aloft at 10kft MSL: Variable 5-20 kt.

KBOI...VFR. Surface winds: SE 5-10 kt.

AIR STAGNATION

A strong upper level ridge will remain centered over the region through the end of the week. This pattern supports the development of steep low level inversions and very weak transport winds. Forecast mixing heights are expected to remain well below 1500 feet AGL for extended periods. These conditions will severely limit ventilation, leading to the accumulation of pollutants in valley locations. Because of the persistent nature of this ridge, the Air Stagnation Advisory has been extended until 5 am MST Friday for all valley zones in southeast Oregon and southwest Idaho.

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.