textproduct: Boise

LONG TERM...Wednesday through Sunday

The forecast period will continue to be dry under high pressure, with continued air stagnation concerns under an inversion. Valley cold pools will keep lower elevation temperatures leaning near to above normal (up to around 5 degrees above), while higher elevations will be 10-15 degrees above normal. Have adjusted higher elevation temps up to better capture the inversion affects. Daytime highs will be above freezing across much of our area, barring the highest peaks. Another implication of the valley cold pool, paired with light winds and generally clear skies, will be patchy fog each morning. The favored locations for fog development will be sheltered mountain valleys and lower basins.

Uncertainty still remains come late Thursday/Friday. As has been advertised, guidance has been in good agreement of a dry cold front/shortwave crossing to our east...with the uncertainty in the westward extent of it. The GFS has been the most ambitious in its western extend, which would bring increased winds and help mix some of the valley inversions, but appears to be trending east towards the Euro and EC-AI solutions. The majority of the Grand Ensemble members still favor that farther east track. Either way, the ridging is expected to persist throughout the long-term with no precipitation chances to be found. Beyond the long-term period, early next week, there are some hints that we may finally break out of this pattern. Stay tuned!

AVIATION

VFR. Areas of fog/low stratus will redevelop overnight, mostly in sheltered mtn valleys and lower basins. MVFR/LIFR in fog/low stratus with mountain obscuration. Surface winds: Variable up to 10kt. Winds aloft at 10kft MSL: W-NW 5-25 kt.

KBOI...VFR. Surface winds: light and variable.

AIR STAGNATION

The building high pressure ridge will maintain a strong temperature inversion across the region through the remainder of the week. Transport winds are forecast to remain very weak, generally less than 10 mph, with mixing heights struggling to exceed 1500 feet AGL in valley locations. These conditions will severely limit atmospheric ventilation and lead to a buildup of pollutants near the surface. There is low confidence (20 percent chance) in the inversion breaking late this week with a weak cold frontal passage. The Air Stagnation Advisory remains in effect for all valley zones in southeast Oregon and southwest Idaho until Friday morning.

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.