FXUS65 KBOI 111655 AFDBOI Area Forecast Discussion National Weather Service Boise ID 955 AM MST Mon Dec 11 2023 .DISCUSSION...An area of light mixed precipitation in far southern Idaho will continue to move southward and weaken through the afternoon. An upper trough approaching from the northwest will initiate scattered showers this afternoon. Any snowfall accumulations will be spotty and light, limited to higher elevations. Many areas are reported fog, which has been locally dense. Visibilities gradually improve through the afternoon. Forecast was updated earlier to expand the fog this morning. && .AVIATION...Mountains obscured and some spotty FZRA has been reported in the Magic Valley. MVFR and local IFR conditions will continue today as low CIGs continue through the period. As precipitation clears out, expect visibilities to gradually improve. Fog and mist this morning may keep visibilities reduced until this afternoon in places not seeing precipitation. Snow levels 4k-5k feet MSL. Surface winds: Mainly variable less than 10 kts, SE 10-15 kt in the Snake Plain. Winds aloft at 10k feet MSL: W-NW 10 kts. && .AIR STAGNATION...High pressure aloft will build over the region on Tuesday and remain in place into next weekend. This will result in a prolonged period of stable conditions with light winds. Given recent precipitation, widespread fog and stratus is expected to form Tuesday night and persist across lower elevations. By Thursday model guidance is showing mixing heights below 2000 feet across all zones with no improvement through Sunday. && .PREV DISCUSSION... SHORT TERM...Today through Wednesday night...Light precipitation will continue through today as the region remains under westerly flow off the Pacific. The cold pool over northern Malheur county and the Weiser basin remains deep enough to support light snow or rain/snow mix down to the surface this morning. Surface temperatures in these areas remain just above freezing so little impact is expected from the snowfall. Otherwise snow levels will hold between 3500-5500 feet. Precipitation will remain light with liquid totals less than 0.20 inches and additional snowfall less than 2 inches through Tuesday morning. Showers will taper off from north to south tonight as drier air aloft pushes into region in advance of a low pressure that will mark an end to the current stretch of unsettled weather. This low will push through the region early Tuesday and is immediately followed by upper ridge. Widespread fog/stratus development is expected Tuesday night into Wednesday across valleys/basins of SE Oregon and SW Idaho as the upper ridge becomes established. Temperatures will remain a few degrees above normal through Tuesday, and closer to normal Wednesday, especially at sites that see fog/stratus formation. LONG TERM...Thursday through Monday...Models continue to agree on maintaining a ridge over the region at least through Sunday. Warm air aloft and light winds will favor development of an inversion, and night and morning fog and low clouds are likely due to moisture remaining from precipitation early in the week. Temperatures will average around 5 degrees above normal, but low cloud cover will restrict diurnal ranges, especially in areas where clouds persist through the day. Deterministic models have come into better agreement on increasing our chances of precipitation on Monday, as moisture increases ahead of a trough off the coast. However, model blends indicate that the inversion will persist, as mixing heights stay below 1000 feet. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...BW AVIATION.....JM AIR STAGNATION...DG PREV SHORT TERM...DG PREV LONG TERM....JT