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000
FXUS66 KOTX 061144
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
344 AM PST Wed Dec 6 2023

.SYNOPSIS...
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Rain will continue today however the air mass will begin cooling
with snow slowly returning to the mountains from west to east.
More seasonal temperatures return Thursday into the weekend. Snow
showers return Thursday night and Friday for some areas then
widespread snow arrives this weekend with another atmospheric
river. Next week looks seasonal and drier than normal.
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&&

.DISCUSSION...

Today: Broad upper-level trough will move onshore today ushering a
cold front through the region and bringing another day of steady
rainfall. As of 2AM, the main axis of rain stretched from the Tri-
Cities northeast through Deer Park and into Bonners Ferry in North
Idaho. This main baroclinic band is expected to buckle northwest
slightly this morning then make a slow track from west to east.
Due to the duration of the rain aimed into NE WA and N ID, these
areas carry the highest probabilities for another 0.50-1.00" of
QPF. Most other locations will be in the range of 0.20-0.50"
except locally lower amounts in the L-C Valley and portions of the
North Cascades. Rainfall intensities will not be similar to those
experienced on Tuesday as the moisture plume is losing its ties
to the subtropics. Additionally, the air mass will begin cooling.
Snow will be returning to the Cascade passes by mid to late
afternoon and Idaho Panhandle mountains Wednesday evening-night.
In the lower atmosphere, the cooling will be much more subtle such
that p-type will remain all rain through tonight.

In North Idaho, Northeastern WA, and around Chelan County, additional
moderate rainfall will keep minor flooding concerns ongoing
including flooded fields, creeks rising near bankfull, and
potential for rock-slides. The Stehekin River which experienced
swift rises to bankfull on Tuesday looks to have crested and will
begin to slowly recede. We are starting off quite mild this
morning with 40s and low 50s common across the eastern third of WA
and North Idaho. Temperatures will only rise a handful of degrees
but as the rain returns, these temperatures will begin cooling.
In Central WA, the cold air has been stubborn to mix out with
temperatures still in the mid to upper 30s. Today`s frontal
passage will bring another chance for some mixing but not
completely sold temperatures will reach full potential and kept
forecast highs on the lower side of guidance.

Thursday and Friday: The trough will be over the Northwest on Thursday
and Friday with cooler air slowly returning to the Inland
Northwest and snow levels eventually falling back to valley
floors. 850mb temperatures cool back near -1 to -2C on Thursday
then -4C on Friday. This will equate to a rain-snow mix for the
lowlands on Thursday the increasing potential for snow Thursday
night into Friday. Precipitation will be less organized and more
chaotic with the trough overhead. Focus will be on a pair of
smaller perturbations rounding the base of the trough and bringing
bands of showers. Details with these features will change over
the next 24-48 hours but given that we can already identify these
features off the coast, there is moderate confidence that these
waves will bring bands of showers to the INW over the next few
days.

The main impacts on Thursday will be on and off snow on the mountain
passes and potential for slick travel conditions. By Thursday
night and Friday, may be dealing with slick travel conditions down
to valley floors across the Camas Prairie, Palouse, Idaho
Panhandle, and into the Spokane-Cd`A area with a lower threat for
snow into Central WA away from the Cascade Crest. At this time,
there is a 10-30% chance for at least 0.1" of new snow for Bonners
Ferry, Sandpoint, Cd`A, and Spokane. Probabilities increase
toward 50-70% for locations like Kellogg, Deary, Pullman, Moscow,
and Winchester. When the dial is turned up to 1", probabilities
for the lowlands decrease below 10% except St Maries, Deary, and
Clarkia which remain near 50% or higher suggesting the Central
Panhandle Mountains and Idaho Palouse are most likely for winter
travel conditions Friday morning. /sb



Saturday and Sunday:
* High confidence in a weak/moderate strength atmospheric river in
  the PNW this weekend.

* Moderate confidence for snow for the valley locations (30-70%
  chance of 2" of snow in Eastern WA/North ID) except a rain snow
  mix in the Eastern Columbia Basin/Palouse Saturday through Sunday.
  There is high confidence for snow in the mountain passes.

* Probability of 8, 12, 18” of snow Saturday-Sunday:
  Stevens Pass: 90%, 70%, 25%
  Lookout Pass: 50%, 15%, 5%

Monday through Wednesday:
* Seasonal temperatures with below average precipitation expected
  early next week with a ridge building in the Northwest US.
/db




&&

.AVIATION...
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12Z TAFs: A plume of Pacific moisture will remain directed into
the Pacific Northwest through Wednesday evening. It will make
slow progress to the east Wednesday afternoon as a cold front
crosses the Cascades between 21-00z. Until then, the Spokane,
Coeur d`Alene, Pullman and Lewiston airports will be in the warm
sector of this system with ceilings generally at or above 4000
feet. As the cold front spreads toward the Idaho/Washington border
between 00-03z, precipitation will be accompanied by a lowering
cloud deck as well as a swath of rain and lower visibilities. More
persistent rain in central and eastern/northeast Washington
Wednesday morning and afternoon will promote ceilings in the 500
to 2500ft range with the lowest cloud deck banked against the
Cascades including Wenatchee. In the absence of rain, periods of
LIFR fog will be possible but these lower visibilities have been
inconsistent over the last 6 hours. Fog is also impacting other
northern mountain valleys including Deer Park, Colville, Republic,
and Winthrop. As the cold front presses through, winds will ramp
up across the eastern Columbia Basin and Palouse with sustained
winds of 15-20 mph possible for a few hours. The wind direction is
favorable for low stratus but should keep the visibilities
elevated given these speeds. This includes KGEG, KPUW, KCOE.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS:
Confidence is moderate at KGEG/KSFF/KCOE that ceilings will remain
above 3000 feet until the cold front arrival Wednesday
afternoon/evening. Main uncertainty for these sites will be
duration of rain throughout the day. Thinking any breaks will be
short-lived with persistent showers forming south of the main rain
axis. Confidence is moderate/high for IFR/MVFR conditions along
the East Slopes of the Cascades and northern mountain valleys
given what has been occurring and lack of strong winds to mix out
these lower cigs through 00z. After 00z, there could be enough
mixing to scrub out the low clouds but thinking this will
redevelop after 06z. Confidence is moderate/high for VFR
conditions until the cold front arrives late in the
afternoon/early evening at KPUW/KLWS.  /sb

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
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&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        49  34  40  29  35  25 /  80 100  70  50  20   0
Coeur d`Alene  49  35  40  30  35  24 /  80 100  80  60  40   0
Pullman        51  36  42  30  36  25 /  30 100  70  70  40   0
Lewiston       57  41  49  35  44  29 /  20  90  50  60  30   0
Colville       43  29  38  25  38  19 / 100 100  60  40  20   0
Sandpoint      45  35  39  30  36  23 / 100 100  90  70  70  10
Kellogg        47  35  38  32  34  27 /  60 100  90  80  80  20
Moses Lake     49  33  45  29  41  25 /  90  80  20  10   0   0
Wenatchee      42  33  42  31  40  27 /  90  60  30  20   0   0
Omak           43  31  40  29  39  25 /  90  70  20  20   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$