Winter Storm in Idaho, April 4, 2023

Area Forecast Discussion
National Weather Service Spokane WA
408 PM PDT Tue Apr 4 2023

.SYNOPSIS...
Wednesday will be a mainly dry day with a good deal of sunshine in
central and eastern Washington. Clouds will be on the increase
Thursday ahead of a slow moving frontal system. Friday into early
next week will feature chances for valley rain and mountain snow
with temperatures at or above average.

&&

.DISCUSSION...

Remainder of the afternoon: It is another afternoon of scattered
snow/graupel/rain showers. As of 230 PM, places that experienced
morning sunshine have destabilized and becoming active on radar.
Convective temperatures are in the mid 40s to near 50, so places
like Spokane, Pullman, and Moscow that remained in the 30s due to
morning clouds have been free of showers thus far. As the sun
goes to work, we may see some of the showers in Stevens and Pend
Oreille counties spread south toward the metro. There is a 20
percent chance of showers in the metro between 4 PM and 7 PM.
Given the delay in destabilization, it is unlikely that
snow/graupel showers will be as disruptive to the evening commute
as they were yesterday on the West Plains, and lightning is
doubtful. In general, radar reflectivity and lightning has not
been as active as yesterday, but lapse rates are comparable to
yesterday so we will be keeping a close eye on radar.

Tonight: Our cold upper trough will move eastward overnight
leading to mostly clear skies, light winds, and chilly
temperatures. The majority of the Inland Northwest will experience
lows in the mid 20 to low 30s which is about 5 to 8 degrees below
average.

Wednesday: With the exception of a 20 percent chance of snow
showers over the mountains along the Idaho/Montana border
Wednesday, the remainder of the Inland Northwest will be dry. Look
for an abundance of sunshine through mid afternoon across central
and eastern Washington before mid and high clouds increase ahead
of our next system scheduled to arrive Thursday into Friday.
Afternoon temperatures will remain below average with highs
ranging from the upper 40s in north Idaho to the mid 50s in
central Washington.

Thursday: A slow moving frontal system will spread precipitation
east of the Cascades during the day Thursday. Snow levels along
the East Slopes of the Cascades will be in the 2000-3000ft range
in the morning and rise to 3500-4500 feet in the afternoon. Given
the daytime arrival of the majority of precipitation, any snow
that falls in the valleys is not expected to accumulate as
temperatures climb into the 40s. /GKoch

Thursday night and Friday night: The upper level ridge over the
western US gets shoved inland while more troughiness sets up over
the eastern Pacific. This will open the door to a series of storm
systems taking aim on the Pacific Northwest. The first of these
systems presses moisture east of the crest Thursday night and
slowly pivots across the region through the day of Friday. The
upper level trough weakens and sheer apart. QPF from this event
shows a slower trend with precipitation continuing into Friday
afternoon. The main area of concern for moderate QPF lies across
north-central WA with rain and mountain snow. For a quarter inch
of rainfall, there’s a 38% chance in Omak and 66% chance in
Colville. Chances for snow in 24 hours from Thursday evening
through Friday show 27% of 2” and 6% of 4” at Sherman Pass, while
at Stevens Pass the snow chances are 54% of 2” and 29% of 4”. With
surface temperatures dipping to freezing Friday morning in the
Methow Valley and Republic, light snow is possible there as well
with 24% of 1” in Mazama and 5% of 1” in Republic. The
precipitation decreases to light showers Friday evening lingering
in the mountains, while southwest breezes are focused in the
Columbia Basin. Temperatures should be near seasonal levels.

Weekend into early next week: The next area of low pressure
arrives and again it looks to take it’s time tracking across the
Inland Northwest, stalling out a bit this weekend. Chances of
precipitation increase Saturday afternoon into Sunday, focused
especially across northeast WA into north Idaho. Meanwhile, much
of central WA will remain drier. With the southwest flow aloft and
building heights inland, surface temperatures should warm a couple
degrees each day with afternoon temperatures in the mid 50s to
lower 60s. The remains of the boundary receives renewed energy
begins to slip slowly to the southeast as the upper trough digs
off the WA by late Sunday. Precipitation increases across extreme
eastern WA into north Idaho Sunday afternoon into Monday and then
gradually decreases on Tuesday. Snow levels remain above 5-6K,
keep snow accumulations confined to mostly the higher elevations.
Daytime temperatures should ease back to seasonal normals by early
next week. The precipitation and higher snow levels this weekend
and early next week will generate rises across the river basins in
extreme eastern Washington and north Idaho, especially on the
Palouse River, Coeur d’Alene River and St. Joe. Flooding is not
anticipated. /rfox.

&&

.AVIATION...
00z TAFs: Scattered snow/graupel/rain showers will dissipate in
the 01-03z timeframe with the loss of afternoon warming. VCSH are
included in the Moses Lake, Coeur d'Alene, and Pullman TAFs. Other
airports like Sandpoint, Kellogg, and Republic will also have a 30
to 50 percent chance brief visibility reductions with graupel or
snow through about 03z. It will be mainly clear overnight, but
with a light southwest boundary layer upslope flow into Spokane
and Coeur d'Alene scattered to broken scattered 1000-1500ft clouds
have been added to the KGEG, KSFF, and KCOE TAFs. /GKoch

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        27  49  31  52  42  51 /  20   0   0  10  50  70
Coeur d'Alene  25  47  29  52  39  48 /  30   0   0  10  40  70
Pullman        26  47  31  53  41  51 /  20   0   0   0  40  70
Lewiston       31  53  36  60  45  59 /  10   0   0   0  30  60
Colville       25  52  27  49  38  49 /  10   0   0  20  60  80
Sandpoint      26  46  29  49  39  46 /  40  10   0  10  40  70
Kellogg        25  43  29  49  39  47 /  40  20   0  10  30  70
Moses Lake     27  54  36  54  43  60 /  20   0   0  30  80  60
Wenatchee      30  54  37  48  41  55 /  10   0   0  50  80  40
Omak           27  53  34  48  41  53 /  10   0   0  30  80  80

&&

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