textproduct: Boise

LONG TERM...Tuesday through Saturday

We remain under a ridge or weak northwesterly flow through Thursday. Heading into next weekend we're looking at a shortwave trough dropping out of Canada along the western edge of the Polar Vortex that has so far spent its winter over Hudson Bay and areas east of the C-Divide. Tonight's model runs bring better agreement on the evolution of the pattern for Fri/Sat with the upper trough bringing light precipitation to e-central Oregon and the w-central Idaho mtns. The deterministic solutions are wetter across these areas. The ensemble mean is lagging in this forecast shift, but does paint the mountains with a 30-40% chance of 2+ inches of snow by Saturday. Its not a lot, but its something and the recent trend is positive.

AVIATION

Widespread IFR-VLIFR in the Snake Plain. Improvement to VFR is expected this afternoon mostly east of KMUO. Expect IFR to hold on along ID/OR border (roughly KONO to vicinity of KEUL) with likely improvement to MVFR between KBOI-KMUO after 18Z. Otherwise VFR conditions in the mtns and across SE Oregon today under mostly clear skies. Surface winds: Variable generally less than 8 kt. Winds aloft at 10kft MSL: Nly 10-20 kt.

KBOI...Should hold at LIFR ceilings with a 30% chance of dropping to VLIFR through 15Z. Conditions will step up to IFR around 18Z with improvement to MVFR 18-20Z. LIFR conditions return 03-05Z tonight and could remain in place well into Sunday. Light surface winds become easterly this afternoon.

Sunday Outlook...Snake Plain will remain IFR well into the day Sunday with some improvement possible in the TWF/JER area. Possible increase in fog/stratus and IFR in basins of SE Oregon to include the KBNO terminal. Light surface winds and NW winds aloft.

AIR STAGNATION

No change to the forecast here. We're in it (the inversion/stagnant air mass) through at least Tue and possibly through Thursday. This means mixing heights of less than 2kft MSL and light winds. Valley locations that have setup under fog/clouds will likely keep these conditions through the Tue- Thur time period (some daytime erosion and thus glimpses of the sun are possible).

BOI WATCHES/WARNINGS/ADVISORIES

ID...Air Stagnation Advisory until 5 PM MST Tuesday IDZ011>014-016-028-033. OR...Air Stagnation Advisory until 5 PM MST /4 PM PST/ Tuesday ORZ061>064.