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.

&&

$$

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DISCUSSION...LC
AVIATION.....SH
PREV SHORT TERM...JDS
PREV LONG TERM....CR