600
FXUS66 KOTX 310622
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1022 PM PST Thu Jan 30 2025

.SYNOPSIS...
High pressure will keep the Inland Northwest dry and cool
today. Snow will return to the region early Friday morning.
Moderate to heavy snow is expected over the Cascades and in the
mountains of the Idaho Panhandle. Moderate snow accumulations are
possible down to the valley floors in far north Idaho and
northeast Washington. Colder temperatures are expected early next
week with additional light snow chances.

&&

.DISCUSSION...

Today through Saturday: Upper level ridge is starting to translate
eastward today and tonight into western and eventually central
Montana signaling a pattern change incoming. Two troughs will
begin to phase together tonight over southeastern BC and increase
the chance of wintry precip regionwide.

Wintry precipitation: Moderate snow will begin this evening in the
Cascades and move eastward overnight. P-types and amounts remain
quite challenging with this event with the many microclimates
eastern Washington and north Idaho. Around Moses Lake area,
expecting a wintry mix Friday morning as temperatures aloft are
still warm from the inversion. Surface temperatures are expected
to rise above freezing around 8-11 AM Friday and the Columbia
Basin will change to rain. Expecting a round of snow to hit right
around commute time for Spokane/Cda area Friday morning, which may
impact the morning commute. Areas that stay cooler and thus
likely to see more snow Friday are the northeast valley areas,
such as Deer Park, Priest River, and Sandpoint. Snow amounts are
going to be highly dependent on saturation and omega in the
dendritic growth zone and topography influences (traditionally
topography favors the northeast valleys for the greatest snow
amounts). Increasing low southwest flow tomorrow morning and
afternoon will promote warm air advection in the Columbia
Basin/Spokane area, bringing a changeover from snow to rain in the
late morning/early afternoon hours. The Cascades and Lookout Pass
are set to receive heavy snow starting tonight and into tomorrow
morning. With a strong frontal passage expected Saturday morning
and 500 mb temperatures sinking down to -40 to 42C, conditions are
favorable for a convergence zone to form. Confidence is low on it
hitting Stevens Pass as current low level flow favors heavier
post-frontal snow around the Lake Chelan area. Expecting snow
showers to continue Saturday in the Cascades and Idaho Panhandle
with an unstable airmass still present.

Probability of 2+ (10pm Thu - 10 pm Fri): Spokane: 50%, Pullman:
10%, Coulee City: 60%, Leavenworth: 60%, Omak: 40%, Sandpoint:
100%, Colville: 60%, Winchester: 30%, Deer Park: 100%

Probability of 5+ (10pm Thu - 10 pm Fri): Spokane: 0%, Pullman:
0%, Coulee City: 0%, Leavenworth: 15%, Omak: 0%, Sandpoint: 30%,
Colville: 0%, Winchester: 0%, Deer Park: 45%

Probability of 12+, 18+, 24+ (10 pm Thu - 4 PM SAT):
- Stevens Pass: 100%, 60%, 10%
- Lookout Pass: 60%, 5%, 0%

Winds: As the low pressure moves through southern BC tomorrow
afternoon, low level winds begin to increase. The NAEFS ensemble
indicates widespread 30+ kt southwest winds and some pockets of
40+ kt winds at 850 mb, which is around the 97th-99.9th percentile
for this time of year. The NAEFS indicates sea level pressures
with the low are around 0.5-1st percentile. With this in mind, I
am expecting a round of south-southwest wind gusts around 35-45
(locally up to 50+) mph in the eastern Columbia Basin, Palouse,
and Spokane area. One limiting factor for wind gusts mixing to the
ground is the fact that the winds will be worse after dark. A
stable boundary layer may prevent the worst gusts making it to the
surface. /DB

Sunday through Thursday: Ensembles are in good agreement with the
large scale pattern with an amplified blocking upper ridge off
the coast with a cold trough settling in over the region. Models
are showing a closed low over Vancouver Island on Sunday gradually
dropping south off the WA/OR coast Monday and Tuesday. The low
position is expected to draw in cold arctic air on Monday through
the middle part of the week, with high temperatures dropping into
the 20s, and low temperatures falling into the single digits and
teens. Some model solutions are going for even colder temperatures
by Wednesday and Thursday suggesting high temperatures in the
teens and a few below 0F readings for the northern valleys. The
low off the coast also has the potential to draw in some moisture
from the southwest Sunday through Tuesday. There is a lot of model
variability with this potential, so did not stray away from NBM
POP`s which are doing for chance POP`s most areas through the
extended forecast. By Wednesday and Thursday the low begins to
fizzle and move inland, leaving the region under a cold northerly
flow and likely drier conditions. JW

&&

.AVIATION...
06Z TAFS: All TAF sites will be at VFR through about 10Z before
conditions begin to deteriorate from west to east to MVFR
conditions and local IFR. KMWH temp profile is supporting -fzra.
It looks to begin around 12Z, but there is a potential for it to
start as early as 10Z. GEG/SFF/COE/PUW/EAT will start out as snow
and will transition to -ra btwn 17-21Z. EAT will remain a -sn
event. LWS is the only TAF site that is not projected to see any
frozen precipitation through the forecast period. Have added wind
shear to GEG/SFF/COE to account for strong southwest winds just
above the surface beginning 18-19Z for GEG/SFF and aft 04Z for
COE.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Confidence is moderate/high in conditions dropping down to MVFR
status around 12/13Z. KGEG in particular has higher confidence
than other sites at dropping to IFR status around 15Z. Confidence
in timing of the transition from snow to rain around 17-21Z for
most TAF sites is moderate, other than KMWH, which has a high
confidence for freezing rain. There is a low chance that PUW could
briefly see -fzra as they transition from snow to rain from
16-19Z.

-----------------------

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

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        30  36  31  36  22  34 /  30 100  90  50  30  40
Coeur d`Alene  29  35  32  36  21  33 /  30 100 100  70  50  50
Pullman        32  40  33  35  23  33 /  10  90  90  70  40  40
Lewiston       35  45  36  41  28  40 /  10  80  80  60  20  30
Colville       27  35  26  35  15  31 /  50 100  90  60  20  50
Sandpoint      28  34  32  36  21  31 /  30 100 100  90  60  70
Kellogg        29  35  32  35  23  31 /  10 100 100  90  70  60
Moses Lake     31  37  28  39  23  37 /  50  80  40  10   0  20
Wenatchee      27  34  27  36  21  32 /  30  70  50  30  20  30
Omak           23  33  25  35  16  31 /  50  90  70  40  10  30

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory until 4 AM PST Friday for Central
     Panhandle Mountains-Coeur d`Alene Area-Lewis and Southern
     Nez Perce Counties-Lewiston Area-Northern Panhandle.

     Winter Storm Warning from 7 AM Friday to 10 AM PST Saturday for
     Central Panhandle Mountains-Northern Panhandle.

     Winter Weather Advisory from 4 AM to 1 PM PST Friday for Coeur
     d`Alene Area-Idaho Palouse.

WA...Air Stagnation Advisory until 4 AM PST Friday for Central Chelan
     County-Lower Garfield and Asotin Counties-Northeast
     Mountains-Okanogan Highlands-Okanogan Valley-Spokane Area-
     Waterville Plateau-Wenatchee Area-Western Chelan County-
     Western Okanogan County.

     Winter Weather Advisory from 4 AM to 1 PM PST Friday for Spokane
     Area-Washington Palouse.

     Winter Weather Advisory from 10 PM this evening to 10 AM PST
     Friday for Moses Lake Area-Upper Columbia Basin.

     Winter Weather Advisory from 10 PM this evening to 10 PM PST
     Friday for Central Chelan County-Northeast Mountains-
     Okanogan Highlands-Okanogan Valley-Waterville Plateau-
     Western Okanogan County.

     Winter Storm Warning from 10 PM this evening to 4 PM PST
     Saturday for Western Chelan County.

&&

$$