textproduct: Boise

DISCUSSION

A strong ridge of high pressure remains over CA over the next several days. This will keep mild west-northwest flow over the area through Sunday. Temperatures will be warm again on Friday and Saturday, although upper level winds weaken each day through Saturday. This will allow a temperature inversion to develop in the lower valleys, and keep high temperatures from being fully realized like the past few days, especially near Ontario. Friday has a chance to be in the low 60s again by Mountain Home and Boise. Have updated the forecast to increase high temperatures on Friday and Saturday.

AVIATION

VFR. Mountains obscured near KBKE KMYL KSNT in low ceilings. Low confidence in patchy fog developing Friday morning in sheltered valleys. Clearing Friday afternoon.

KBOI...VFR. SE winds 5-10kt at night becoming NW 5-10kt during the day.

Weekend Outlook...Mostly VFR with low confidence in low stratus and fog in sheltered valleys each morning. Light winds.

PREV DISCUSSION

SHORT TERM...Tonight through Saturday night...High pressure will remain in place tomorrow through the weekend, continuing drier and warmer conditions. Temperatures are expected to remain on the warmer end tomorrow, with peak valley temperatures in the lower to mid 50s. A cooling trend will bring valley daytime temperatures down into the lower 50s and mountain temperatures into the lower 40s Saturday. Colder nighttime temperatures in the lower to mid 30s will be expected tonight and Friday night. Patchy to dense fog will remain likely over sheltered mountain valleys later tonight through Friday early morning. Winds will be Southeast/Southwest and mostly calm under 10 mph for nearly all areas tomorrow through Saturday. Clearing skies and weak winds tomorrow through the weekend will continue to favor valley inversions, keeping the air stagnation advisory intact for valley areas until late Sunday.

LONG TERM...Sunday through Thursday...The upper-level ridge axis will gradually shift eastward on Sunday, allowing for slightly cooling temperatures and an increase in cloud cover as a weak low- pressure system skirts to our south over southern Nevada. The ridge will further weaken on Monday as strong westerly flow increases ahead of the next moist system approaching the Pacific Northwest coast. Until this time, inversion and stagnant conditions will persist in the valley into Monday. The inversion is unlikely to be fully removed until a much stronger system moves in late Tuesday into Wednesday. However, scattered showers are possible across the area with 40-70% chances Monday night into Tuesday, accompanied by high snow levels between 7,500 and 9,500 feet MSL.

Another Atmospheric River (AR) event could return to the Pacific Northwest as early as Tuesday night, setting the stage for another round of widespread precipitation. Snow levels will likely remain elevated initially, around 7,000 to 8,500 feet MSL, thanks to warm southwest flow, but could lower back to 5,000 to 6,000 feet MSL by Wednesday. There is high confidence that this system will affect the region late next week, though differences remain in the projected strength of the upper-level ridge and the resulting warmer air later in the week. The ensembles largely favor the ridge remaining over the Intermountain West Wednesday into Thursday, keeping warm air and higher snow levels in place. However, a minority of ensembles introduces the possibility of colder air moving in from the north, which would lead to lower snow levels and temperatures but far less overall precipitation. Given this lingering uncertainty in the pattern's evolution, current forecast chances for any significant accumulation of rain or snow are minimal over our region. Temperatures are expected to remain 10 to 20 degrees above normal through the long-term period, with later weekdays showing the best potential for significant cooling.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Air Stagnation Advisory from 5 AM Friday to 5 AM MST Monday IDZ012-014-016-033. OR...Air Stagnation Advisory from 5 AM MST /4 AM PST/ Friday to 5 AM MST /4 AM PST/ Monday ORZ061>064.