368
FXUS66 KOTX 252350
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
350 PM PST Wed Dec 25 2024

.SYNOPSIS...
Widespread mountain snow and valley rain or snow is expected
tonight and Thursday. Moderate to heavy snow is expected across
north-central Washington in particular with impacts to travel
likely. The weather remains unsettled through the holiday weekend.
Check mountain pass forecasts and conditions often before
traveling.

&&

.DISCUSSION...
Christmas Night through Thursday:  The storm system that has been
discussed in great depth over the last few days has arrived and
snow has started to fall in the Cascades and portions of Central
WA. This activity is light but will be picking up in intensity
this evening and through the overnight hours. Models remain in
good agreement of a solid 0.50-1.00" or more of QPF for nearly all
areas of the INW west of a line of Sandpoint to Wenatchee. There
remains some differences with the depth of the sfc-850mb low over
NW WA which will have some ramifications on timing of snow levels
and snow amounts...mainly across NE WA and N ID. In Central WA,
there is high confidence for moderate to heavy snowfall and this
will likely come with snowfall rates of 1-2 inches per hour.
Heaviest snowfall will be west of a line from Wenatchee to
Colville with widespread amounts of 4-7 inches and locally near a
foot in the upper Cascade river valleys. Nearly two feet is
expected through Thursday afternoon on Stevens Pass.

For NE WA and N ID, the precipitation will be a bit more progressive.
This area will also lack cold air and cold air damming like we
are observing near the Cascades. Consequently, the presence of the
warmer sector will result in lower probabilities for significant
lowland yet still forecasting appreciable amounts in the
mountains. Let`s dive in the surface details some more below...

The current surface observations across Central WA are cooler than
expected and forecast has been adjusted for locations like
Wenatchee, Chelan, and into Omak to account for more snow vs
rain/snow mix based on the latest readings. Thinking these will
not change much with the low sun angle and high precipitation
intensity arriving overnight. Winter storm warnings look good
where issued in the Okanogan Highlands/Valley, Waterville Plateau,
and into the East Slopes of the Cascades. Wenatchee to Chelan has
also been upgraded. The main uncertainty with this area is local
downsloping off Mission Ridge into Wenatchee limiting QPF and snow
amounts. This does not tend to impact Ardenvoir, Entiat, and
Chelan.

The forecast is a bit more complex for the valleys of NE WA, N ID, and
across the Upper Columbia Basin. Surface temperatures vary from
33-38F. Snow for these areas (Grand Coulee, Davenport, Airway
Heights, Deer Park, Bonners Ferry, and Sandpoint) come with lower
confidence and will be very dependent on the intensity overnight.
The atmosphere still supports snow but accumulations with these
temperatures can be tough to achieve.

For the lower Basin, L-C Valley, Palouse, and Camas Prairie...p-type
looking to be mostly rain with periods of wet snow mixed in.

Forecast winds have also been increased for Thursday morning across the
Eastern Columbia Basin, Palouse, Camas Prairie, and into the
Spokane-Cd`A Area, and Central Panhandle Mountains. Numerous hi-
res models showing wind gusts 40-45 mph with isolated gusts in
excess of 50 mph on the Camas Prairie and in the foothills of the
Blue Mountains. Consequently, wind advisories have been issued
starting in the Camas Prairie around midnight and expanding
northward early Thursday morning. Given the saturated grounds,
isolated tree damage and power outages are the main concerns
though high profile vehicles should exercise caution. Winds will
largely be from the south and southwest.

Majority of the impactful lowlands snow will be done falling by
midday Thursday. Snow will continue in the mountains and on the
passes. Gusty southwest winds accompanying a frontal passage will
allow for increased mixing and temperatures above freezing for
most areas below 3000 feet. Those traveling over Lookout Pass and
the Cascades should be prepared for additional snow impacts with a
consistent barrage of snow showers. Snow showers will decrease in
intensity Thursday night but tough to find a completely dry
period with the next storm system approaching quickly on its
heels. /sb

Friday through Wednesday: The weather remains unsettled through
the extended period. The region will see periods of mountain snow
and valley rain or snow. Any valley snow accumulations through the
weekend look to be very light. For those traveling over the
passes through the weekend, the probabilities of 4, 6 and 8 inches
over 24 hours are as follows:

  4 AM Friday to 4 AM Saturday
Stevens Pass: 80%, 70%, 50%
Snoqualmie Pass: 40%, 35%, 30%
Blewett Pass: 60%, 35%, 20%
Sherman Pass: 25%, 5%, 0%
Lookout Pass: 70%, 55%, 30%

  4 AM Saturday to 4 AM Sunday
Stevens Pass: 55%, 40%, 20%
Snoqualmie Pass: 30%, 25%, 15%
Blewett Pass: 25%, 10%, 2%
Sherman Pass: 5%, 0%, 0%
Lookout Pass: 40%, 30%, 10%

  4 AM Sunday to 4 AM Monday
Stevens Pass: 75%, 60%, 50%
Snoqualmie Pass: 55%, 40%, 30%
Blewett Pass: 40%, 20%, 10%
Sherman Pass: 25%, 10%, 1%
Lookout Pass: 80%, 70%, 50%

Temperatures will remain above average through the
period...sometimes by as much as 10 degrees. That is highs in the
mid 30s to mid 40s and lows in the mid 20s to mid 30s. Models are
hinting at however, temperatures cooling down enough for valley
snow come Tuesday night/Wednesday. While 500 mb heights indicate
a ridge over the region and higher heights than what we are seeing
now, temperatures lower in the atmosphere cooler. 850 temps look
on average to be -3 to -5C. There is a 30-50% of an inch of snow
for the Spokane/CdA area and eastern Palouse. Probabilities
increase further as you head into northern WA and ID and towards
the Cascades.

Winds will increase again on Saturday the 28th, with a 30-40%
chance of gusts to 30 mph or higher across Adams and Whitman
counties. Garfield and Asotin have a 50-60% of seeing gusts over
30 mph. As you head north into Lincoln and Spokane counties the
probabilities go down to 10-25%. /Nisbet

&&

.AVIATION...
00Z TAFS: A moisture laden winter storm system to bring widespread
restrictions to the forecast area through 18z THU. Widespread IFR
conditions come with a 70% chance or higher. A stubborn low deck
over LWS this afternoon does not look favorable to erode until
the pcpn arrives though this comes with low confidence. Tricky
forecast for COE-GEG-PUW which could bounce around from snow and
rain. Pcpn intensity will play a large role with temps of 33F or
warmer. GEG-COE carry 60% chance for a slushy inch of accum and
snow ranges are from a few tenths to 3 inches. Current obs at EAT
support snow and should change very little with incr confidence
for significant snow accumulations. Otherwise, heavy snow will
impact the Cascades and northern mountains including Leavenworth,
Winthrop, Omak, and Republic. Light to moderate snow expected for
Colville to Bonners Ferry to Sandpoint and Mullan. Largely rain
for the lower Columbia Basin. Elevated SE winds will keep
visibility elevated but widespread MVFR to IFR conditions expected
for the forecast area. Strong winds developing in the eastern
Basin shortly after 17z with potential for gusts 30-40 kts. Prior
to that, LLJ develops and LLWS was added to some TAFS

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Confidence is very low when fog will break at KLWS this evening.
Confidence is moderate to high for a significant winter storm in
Central WA and widespread IFR conditions. Main uncertainty with
the forecast is exact p-type and how effective snow will
accumulate at GEG, COE and other low elevation sites into THU AM.
Also some uncertainty with peak wind gusts in SE WA and NC ID
Thursday morning. Isold gusts could reach 50-55 mph. /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

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        33  43  34  39  35  44 / 100 100  20  80  80  50
Coeur d`Alene  31  41  34  39  35  43 /  90 100  30  80  90  70
Pullman        35  43  34  39  35  43 / 100 100  30  90  90  60
Lewiston       37  51  39  45  40  51 / 100  90  20  80  70  50
Colville       33  37  29  37  30  39 / 100 100  20  80  80  60
Sandpoint      31  38  34  37  33  39 /  90 100  50  90  90  90
Kellogg        33  39  33  38  36  39 /  80 100  50  90  90  90
Moses Lake     34  44  34  42  37  46 / 100  40  30  70  70  20
Wenatchee      32  35  32  38  35  41 / 100  50  40  70  80  40
Omak           32  35  31  37  33  40 / 100 100  20  70  80  40

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory from 1 AM to 1 PM PST Thursday for
     Central Panhandle Mountains-Northern Panhandle.

     Wind Advisory from 6 AM to 3 PM PST Thursday for Central
     Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse.

     Wind Advisory from 2 AM to 11 AM PST Thursday for Lewis and
     Southern Nez Perce Counties.

WA...Wind Advisory from 6 AM to 3 PM PST Thursday for Lower Garfield
     and Asotin Counties-Spokane Area-Upper Columbia Basin-
     Washington Palouse.

     Winter Weather Advisory until 7 AM PST Thursday for Upper
     Columbia Basin.

     Winter Weather Advisory until 1 PM PST Thursday for Northeast
     Mountains.

     Winter Storm Warning until 1 PM PST Thursday for Okanogan
     Highlands.

     Winter Storm Warning until 7 AM PST Thursday for Wenatchee Area.

     Winter Storm Warning until 7 AM PST Thursday for Okanogan Valley-
     Waterville Plateau.

     Winter Storm Warning until 1 PM PST Thursday for Central Chelan
     County-Western Okanogan County.

     Winter Storm Warning until 10 PM PST Thursday for Western Chelan
     County.

&&

$$