021 FXUS65 KBOI 061620 AFDBOI Area Forecast Discussion National Weather Service Boise ID 920 AM MST Sun Nov 6 2022 .DISCUSSION...A weak short wave upper trough will develop scattered light rain and snow showers this afternoon in Idaho from the Snake Basin northward. After brief clearing this evening our CWA will come under the influence of an upper trough deepening southward from the Gulf of Alaska and western Canada. The trough is beginning to close off an upper low near Vancouver Island. Models move the low southward along the coast tonight through Tuesday. A surface cold front will move across eastern Oregon tonight with light rain and snow showers. The front and showers will reach western Idaho before sunrise Monday. Shadowing by the Owyhee Mountains under southwest flow aloft will limit precipitation in the Treasure Valley as the front passes. The front will moisten again later Monday as it gets into south-central Idaho. Western Idaho and eastern Oregon will become drier. Current forecast reflects these model details well. No updates for now. && .AVIATION...Generally VFR conditions today. Cold front will bring periods of MVFR/IFR in light/moderate snow showers across SE Oregon, central mountains of Idaho, and the NV/ID border area this evening into Monday morning. Mountains obscured at times. Snow levels 4500-5500 ft MSL this afternoon, lowering to roughly 3000-4500 ft by Monday A.M. Surface winds: SE to S 5-15kt this morning, becoming SE to SW 10-20kt with gusts 25-30kt after 18z. Winds aloft at 10kft MSL: W-SW 25-40kt, then S-SW 35-50kt after 07/03Z. && .PREV DISCUSSION... SHORT TERM...Today through Tuesday night...Brief break in the weather this morning as the region remains between systems. Satellite showing the next cold-core low pressure system off the coast of British Columbia which will continue southward along the Pacific Northwest Coast today. This will allow the upper level flow to shift to the southwest which will increase the upper level moisture for clouds and showers this afternoon mainly across Southwest Idaho. However, 30-40 kt 700 mb southwesterly flow and 10-20 kt southeasterly flow at the surface will likely limit precipitation in the Treasure Valley due to shadowing. A cold front will move from west to east late tonight through Monday morning. High-res models show a line of showers ahead of the front as it moves across the region but again limits precipitation in the Treasure Valley due to shadowing. Believe the forcing from the front will allow only minimal rain accumulations in the valley around 12z. Snow levels will remain high ahead of the front around 6000-7000 feet and lower to near 3000 feet by Monday evening. Higher precipitation amounts will be possible in South- Central Idaho as the front interacts with deeper moisture. The low center will reach the Oregon coast Tuesday morning which will shift the bulk of moisture to the east. This configuration will leave the forecast area under relatively dry divergent flow aloft through Wednesday morning. Southwesterly flow aloft will continue with increasing southeasterly flow within the boundary layer. Despite the cold frontal passage, temperatures up to 700 mb will remain mild through the period, still below normal but at or above freezing in the valley. LONG TERM...Wednesday through Sunday...Deterministic models along with clusters/ensemble members show the next upper low that dives southward along the Pac Nw coast early in the week continuing southward to the central coast of California Wednesday. The bulk of the dynamics will stay south of the region, but the cold air associated with the elongated upper trough should bring areas of snow showers to the region with light/moderate accumulations to the Boise National Forest and NV/ID border area. The trough and upper low will kick eastward Thursday as a high amplitude ridge builds over the Pacific Northwest Thursday afternoon through Saturday morning. This ridge will extend north well into British Columbia. Pockets of gusty winds are possible, especially across the Magic Valley region Thursday. By the weekend, storm systems will begin to undercut the upper ridge and move into Northern California. How well these systems hold together moving further inland is not well resolved among the models at this time. The GFS is the most excited about bringing another round of precipitation into the region, whereas the ECM/Canadian dampen it out. NBM keeps the forecast dry for the weekend, and given that the ridge tries to remain in the area, will continue a dry forecast at this time. Temperatures will remain about 10-15 degrees below normal. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...LC AVIATION.....SH PREV SHORT TERM...JDS PREV LONG TERM....CR