-- Discussion containing changed information from previous version are highlighted. --
563
FXUS66 KOTX 130548
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
948 PM PST Sun Jan 12 2025

.SYNOPSIS...
Monday through Wednesday will be dry across the region as high
pressure builds in. Snow chances return toward the end of the new
work week mainly in the mountains, with a system that may start to
draw the coldest air of the season into the region so far this
season.

&&

.DISCUSSION...


Tonight through Wednesday: A positively flopped over upper
level ridge of high pressure will generally remain in place through
Wednesday. The ridge axis placement remains more or less in the
vicinity of Washington. No disturbances are expected to overtop this
ridge between now and Wednesday this will allow for subsidence
inversions to linger on with low level boundary layer moisture to
remain pooled near the surface. As a result a boring stagnant
weather forecast consisting of low clouds and fog remains in place
in some shape/form. Forecast temps remain slightly on the cool side
of what would be considered normal for this time of year given the
poor mixing. /Pelatti

Wednesday Night and Thursday: A significant pattern change will
arrive on Thursday morning. The strong high pressure ridge
controlling the weather over the Pacific Northwest early in the
week will be flattened by a vigorous system moving through B.C.
into the Canadian prairies Thursday. There is good agreement
between the ensembles that the cold front with this Canadian
system will cross the Cascades Thursday morning and clear north
Idaho by mid afternoon. Locally gusty west winds will be the most
noticeable weather change with this front. Given our resident
chilly and stable air mass, the strongest winds generated by the
National Blend of Models is over the high terrain of the Cascade,
the Blue Mountains, and the ridges of north central Idaho. With
700mb winds of 40 to 45kts, it is reasonable to expect gusts of 40
to 50 mph in the high terrain exposed to west winds. ECMWF
ensemble guidance has average wind gusts of 25 mph for Pullman and
on the Waterville Plateau including the high terrain around
Wenatchee. The wind Thursday followed by cold advection Thursday
night should disperse the majority of our low clouds in central
and eastern Washington by Thursday night. Precipitation with
Thursday`s front does not look impressive. The surface low with
this system and the majority of the synoptic lift will remain
well north of the Canadian border. Other than some 20 to 40
percent chances for snow in the mountains with the frontal
passage, measurable precipitation chances will be 15 percent or
less for our lowlands.

Friday through next weekend: Confidence is increasing that our
coldest air mass of the season will bleed into the Inland
Northwest over the weekend. There are differences between the
ensembles on how strong the push of cold air from B.C. will be.
The Canadian ensemble mean carries the sharpest and coldest 500mb
trough while the GFS and ECMWF ensembles the Inland Northwest
more gently keeping the majority of the Arctic air east of the
Continental Divide. By Sunday morning, the Canadian Ensemble Mean
has -14C at 850mb over Spokane while the GFS and ECMWF are closer
to -10C at 850mb. The National Blend of Models (NBM) forecast
most closely resembles the ECMWF forecast for high temperatures
with highs in the 30s Friday and 20s to mid 30s Saturday and
Sunday as chilly air continues to bleed through the Okanogan
Valley and valleys of north Idaho. Low temperatures from the NBM
are cold...colder than MOS guidance as well as GFS and ECMWF raw
guidance. Since the NBM hans`t "seen" any truly cold air so far
this season, it doesn`t had a chance to bias correct itself on a
clear and cold air mass. With that in mind, we blended our low
temperature forecast toward MOS this weekend yielding lows in the
teens and 20s with a handful of single digits in our northern
valleys. /GKoch

&&

.AVIATION...
-- Changed Discussion --
06Z TAFS: Dense, LIFR fog has formed over the West Plains (KGEG)
and KCOE while IFR stratus lingers over KSFF. There is low
confidence for these conditions to change very much through 16z.
Breaks in the high clouds will likely allow fog to expand around
Pullman and and vcnty of KLWS. In Central WA, drier air drifting
in from the north between Omak and Moses Lake leads to low
confidence for fog development but heavy frost is likely.
The HREF does expand 20-30% probabilities for vis 1/2 mile or
less from Spokane westward into Moses Lake by Monday morning
(15-17z). This conflicts with the HRRR guidance which is capturing
the drier air and indicates a weak push of the drier air into
Spokane-Cd`A between 14-16z. Given the general light boundary
layer winds, forecast leans toward TAF climatology for the current
obs which carries a 60% for current observations to persist and
some improvement after 19z. Confidence is low for the low clouds
to completely erode. Boundary layer winds will also begin to shift
to more southeast drawing higher dewpoints into Central WA and
increase probabilities for restrictions around Moses Lake, Wilbur,
and eventually Wenatchee heading into Monday evening and night.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
General low confidence between PUW-LWS with high clouds slowly
drifting south and increasing radiational cooling. Would not rule
out LIFR fog at PUW and to some extent, LWS. Forecast confidence
very low for Moses Lake. Some hi-res models suggest IFR/LIFR fog
development by daybreak. Confidence generally low for timing for
improvement for any sites on Monday under the influence of high
pressure aloft promoting stable weather conditions and light
winds. /sb


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

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

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        24  29  25  30  25  35 /   0   0   0   0   0   0
Coeur d`Alene  24  30  24  32  25  37 /   0   0   0   0   0   0
Pullman        26  33  25  36  27  39 /   0   0   0   0   0   0
Lewiston       30  39  30  39  31  42 /   0   0   0   0   0   0
Colville       17  29  21  30  24  35 /   0   0   0   0   0   0
Sandpoint      25  30  25  33  26  36 /   0   0   0   0   0   0
Kellogg        28  31  23  35  25  39 /   0   0   0   0   0   0
Moses Lake     25  34  27  35  27  36 /   0   0   0   0   0   0
Wenatchee      26  34  28  33  28  33 /   0   0   0   0   0   0
Omak           18  30  24  30  25  34 /   0   0   0   0   0   0

&&

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

$$