textproduct: Boise

DISCUSSION

Seeing thin high clouds over the area this morning, moving from north to south as we remain on the east side of an upper ridge. Webcams are showing a few spots of lower clouds in the Long Valley near Cascade, but otherwise not seeing much fog/stratus this morning. The inversion will strengthen today with warming aloft accompanying the building upper ridge. Lowest elevations of the Snake Plain will see little change in high temperatures from yesterday, with more notable warming in the mountains (4-8 degrees). Forecast is on track for today and Air Stagnation Advisory remains in place through Thursday.

AVIATION

VFR today. Patchy low cloud near Cascade (U70) and other central ID mtn valleys through 18Z. Similar development expected again tonight after 10Z. Surface winds: E-SE 5-15 kt. Winds aloft at 10kft MSL: W 10-15 kt.

KBOI...VFR. SE surface winds through the day.

AIR STAGNATION

An upper level ridge will build over the region today and remain overhead through Wednesday. This pattern will create stagnant conditions in the valleys with poor mixing and light winds as a temperature inversion strengthens. Daytime mixing heights will be below 2000 feet AGL through at least Thursday. An Air Stagnation Advisory is in effect for most valley locations through early Thursday.

PREV DISCUSSION

SHORT TERM...Today through Wednesday night...An upper level ridge building along the coast will move overhead Monday through Wednesday. This will bring dry and stable conditions with a temperature inversion that strengthens through midweek. Temperatures will gradually warm through Wednesday, especially at higher elevations that are above the inversion, but will see little change in the lowest valleys across southeast Oregon and southwest Idaho where the inversion will be strongest. Patchy valley fog and stratus is possible, although dry air will limit potential. Highs by Wednesday will be 5 to 10 degrees above normal in most areas, except near normal in the Lower Treasure Valley due to the inversion.

LONG TERM...Thursday through Sunday... A return to an active pattern expected through the extended period. A deep trough off the coast will help to steer a weaker trough near the California coast northward. This weaker trough will be accompanied by subtropical moisture, and rain or snow chances will increase from the south on New Years Day, reaching 40 to 70 percent Thursday night and Friday. Given the air masses originating from the subtropics, conditions will be milder with snow levels increasing to 5000-6500 feet (possibly as high as 7500 feet). The deep trough off the coast will send shortwave impulses inland over the weekend, bringing a 30 to 50 percent chance of rain and high elevation snow. These will bring cooler air with snow levels gradually lowering to 3500-5500 feet by Saturday. Moderate precipitation totals are expected Thursday through Sunday with significant snow accumulations limited to higher peaks. Temperatures through the period will average 5-10 degrees above normal.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Air Stagnation Advisory until 10 AM MST Thursday IDZ012-014-016-028-033. OR...Air Stagnation Advisory until 10 AM MST /9 AM PST/ Thursday ORZ061>064.