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000
FXUS66 KOTX 282359
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
359 PM PST Tue Nov 28 2023

.SYNOPSIS...
Stagnant conditions with periods of freezing fog and low clouds
will continue through early Thursday. A significant pattern
change at the end of the week will lead to several rounds of snow
for most of the Inland Northwest with the potential for heavy snow
near the Cascades. Much warmer weather will develop early next
week with the wet weather continuing.

&&

.DISCUSSION...
Through Wednesday night:
Generally light winds and stagnant conditions will enable nuisance
freezing fog and areas of low clouds to continue through Wednesday
night. The low stratus deck, in particular, has maintained its
stranglehold across much the Columbia Basin and Cascade-adjacent
valleys, occasionally drifting into the Palouse and Lewiston areas
as well. The areas of freezing fog are likely to expand overnight
tonight. In addition, the Air Stagnation Advisory remains in
effect until late Thursday morning. Daytime temps to run about 5
degrees below normal on Wednesday.

...Much wetter and snowier pattern expected to kick off December...

Thursday through Tuesday: Ensembles continue to have the ridge
flatten and shift East as a trough begins to dig south along the
coast. The Pacific Northwest will impacted by a moisture plume being
pushed into the region by a Gulf of Alaska Low and a high pressure
off the California Coast. Ensembles are bringing a series of
shortwaves through the region starting late Thursday and lasting
into next week. The Inland Northwest can expect several rounds of
precip into to the start of next week. Ensembles are steadily
increasing the amount of precip associated with these waves.

The first wave late Thursday into Saturday will bring widespread
snow to the region with the heaviest snow amounts in the Cascades.
The Cascades mountain passes could see 10 to 15 inches. The amounts
across the Basin are 1 to 3 inches. Northern Valleys are expecting
around 2 to 4 inches. The Idaho Panhandle could get 1 to 4 inches.
Lookout Pass is expected to receive 4 to 8 inches. Morning commutes
should expect snowy conditions.

The second wave will be Sunday into Tuesday. Temperatures will be
a warming trend with the Southerly flow pattern. It will change
the precip type across the Basin to rain or a rain/snow mix.
Portions of the northern Basin could see an additional inch.
Cascades will again receive the brunt of the moisture. Pass could
receive another 12 to 18 inches. The northern valleys and Idaho
Panhandle should see an additional 1 to 3 inches. Lookout Pass
could see another 6 to 8 inches. By Tuesday, the warmer surface
temperatures will keep the Basin and valleys in a rain precip type
with snow for the mountains. Snow levels are expected to climb
above 4000ft. Highs for the period will be in the 30s. Highs will
then climb into the 30s and low 40s by Monday. Lows will be in the
upper teens and 20s through Sunday. Lows will then climb into the
30s for the start of the week. /JDC

&&

.AVIATION...
00Z TAFs: IFR/LIFR cloud stratus layer extending from Moses Lake
to Pullman southward into the Lower Columbia Basin is expected to
expand north and east tonight as boundary layer winds are light
out of the south and southwest. None of the models are handling
the north and east extent of this cloud deck currently so forecast
based mainly off satellite trends and expected trend of the
stratus to the north and east overnight. Pullman has already gone
down to a 1/4SM, with the fog, and expected to reach KGEG around
03-04z, and KSFF near 06z. There is lower confidence for KCOE as
the progress may slow with northeast winds still in this area.
KEAT carries lower confidence as well, as the stratus slowly
expand from Ephrata and Moses Lake toward the west. Once the
stratus moves in, it is likely to hang around through the day
Wednesday due to light boundary layer winds although some gradual
lifting of the stratus layer is expected.


FORECAST CONFIDENCE AND ALTERNATE SCENARIOS: Low confidence how
long KPUW will stay at 1/4SM. With models showing not much of an
east wind overnight and the low level cold pool quite strong,
forecast keeps at 1/4SM with some indication of a light west-
northwest boundary layer wind keeping the fog in place. Low
confidence for timing when the low cloud deck moves into Lewiston.
High confidence the fog bank will move into GEG this evening, with
moderate confidence of visibility down to 1/4SM. JW

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https://www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        19  31  19  33  24  35 /   0   0   0  10  60  80
Coeur d`Alene  21  34  20  34  26  34 /   0   0   0  10  70  80
Pullman        21  36  20  33  26  36 /   0   0   0  10  80  80
Lewiston       26  37  25  36  31  43 /   0   0   0  10  60  60
Colville       15  34  14  34  18  32 /   0   0   0  10  50  80
Sandpoint      20  34  20  35  23  31 /   0   0   0  10  70  90
Kellogg        27  38  24  34  30  34 /   0   0   0  10  80  90
Moses Lake     18  31  18  34  21  39 /   0   0   0  10  30  50
Wenatchee      26  36  25  32  25  36 /   0   0   0  10  30  60
Omak           22  36  22  34  24  36 /   0   0   0  10  20  50

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory until 11 AM PST Thursday for Central
     Panhandle Mountains-Coeur d`Alene Area-Northern Panhandle.

WA...Air Stagnation Advisory until 11 AM PST Thursday for Central
     Chelan County-Moses Lake Area-Northeast Mountains-Okanogan
     Highlands-Okanogan Valley-Spokane Area-Upper Columbia Basin-
     Waterville Plateau-Wenatchee Area-Western Chelan County-
     Western Okanogan County.

&&

$$