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000
FXUS66 KOTX 251009
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
309 AM PDT Mon Oct 25 2021

.SYNOPSIS...
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The chance for more rain and mountain snow will persist through
much of the week. The north Cascades will likely receive several
rounds of accumulating snow in the high terrain. Tuesday and
Wednesday will be windy across the Columbia Basin, Palouse, and
West Plains with gusts of 30 to 40 mph. A wet and windy weather
pattern is expected to continue into late week.
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.DISCUSSION...

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Monday and Tuesday: A potent low pressure system continues to
spin off Vancouver Island this morning however this system has
reached its peak intensity on Sunday and will continue to fill and
eject across southern BC over the next 24 hours. The system will
continue to influence the weather over the Inland NW drawing
breezy winds into its center and bringing on/off precipitation
chances. A second low will track across the Eastern Pacific on
Tuesday riding along a 160kt jet. This system will remain parked
much further north in the Gulf of AK but the strong westerly jet
on its southern periphery will nose into Washington ushering a
midlevel warm front and one more band of precipitation.

As of 2AM...the occluding front that ushered heavier showers across
the region Sunday evening was drifting east through the Idaho
Panhandle and should be exiting into Western Montana early this
morning. Behind this front, a dry slot has moved into the region
and is providing a break in the precipitation for much of Central
and Eastern WA. A second boundary will cross into Central WA this
afternoon renewing the threat for light showers. Most of the
activity this afternoon will remain west of a line from Colville
to Ritzville. Communities east of this line such as Sandpoint,
Spokane-Cd`A, and Moscow-Pullman will experience a mix of sun and
clouds and generally dry conditions. Ample surface heating in the
afternoon may spark a few showers over the mountains of NE Oregon,
some which could drift toward the Camas Prairie. A few hi-res
models also suggest a few lightning strikes with this activity but
this has little support from the SREF/HREF so opted to leave
mainly a mention of showers.

This boundary will track east Monday evening and night spreading
showers into the remainder of Eastern WA and the Idaho Panhandle.
Rainfall amounts with these showers today and tonight will
generally be from 0.05-0.20". Heavier amounts, from 0.50-1.00"
will impact the Cascade Crest as 700mb flow shifts from south to
west. Precipitation will remain light on Tuesday but will become
more widespread as a warm front lifts north to south. The front
looks to lift into northern WA/ID by late Tuesday afternoon
allowing for drier weather to return to the East Slopes and
Columbia Basin prior to sunset.

As for winds the next few days...breezy southerly winds will be in
place today then south to southwest Tuesday. Wind speeds of 10-20
mph are to be expected for much of the open Basin and into the
Okanogan Valley. Wind gusts will be on the order of 25-35 mph.
Overnight temperatures will remain mild when compared to average
with nearly all valleys expected to remain above freezing.
Afternoon highs will fall close to those average numbers with
highs in the 50s each day.

Tuesday night and Wednesday: The Polar jet will nose into Washington
state Tuesday night then migrate northward on Wednesday. This
will bring the "potential" for several hours of strong winds
Tuesday night/Wednesday morning. The signature showing up in the
synoptic scale models does indicate the potential for mountain
waves as a 50-80kt jet from 700-500mb crosses the Cascades but
these are not always sure events to get strong winds to the
surface and several of the ingredients in this case do not align
with our typical mountain wave events. Consequently, this event
comes with plenty of uncertainty but we cannot ignore the fact
that several of the hi-res models are showing wind gusts near 50
mph along the ridgetops of the Cascades and possibly over the
Waterville Plateau. This is something we will need to keep a close
eye on in the coming days. Otherwise, Tuesday night and Wednesday
will feature gusty winds west to southwest for most of our area
outside the sheltered northern valleys. Sustained speeds of 15-25
mph will be accompanied by gusts of 25-35 mph. The West Plains,
Palouse, and foothills of the Blue Mountains will also need to be
monitored closely for potential stronger gusts as a 45kt jet
develops just a few thousand feet off the ground.

This more typical flow pattern will lead to a large rain shadow in the
lee of the Cascades and across the Columbia Basin but numerous
orographic showers are expected into the rising terrain of the
Idaho Panhandle, Northeastern Mountains of WA, and Cascade Crest.
Local heavier bands setting up on the Cascade Crest could lead to
moderate snow accumulations for Washington Pass and possibly down
to Stevens Pass at times. /sb

Wednesday night through Sunday:
Unsettled and occasionally breezy conditions will continue through
the extended portions of the forecast. A warm front is expected to
push into the Inland NW Wednesday night into Thursday. Rain and snow
is anticipated, with snow levels (originally around 4000 ft or so)
lifting through the day.

Daytime temps Thursday and Friday look to run a bit above normal,
with signs pointing to a drier and colder scenario setting up for
Saturday and any All Hallows` Eve shenanigans. /KD
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.AVIATION...
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06z TAFS: Widespread precipitation is pushing across eastern WA
and north ID as of late evening and this will continue to impact
the eastern sites (GEG SFF COE PUW and LWS) at times through
09-11z. We went with VFR cigs however it would not be surprising
to see some brief MVFR cigs forming, especially for COE and PUW.
Farther west at MWH there are some showers in the vicinity, but
they will be moving out shortly. Once the precipitation ends later
this morning, there will also be a small risk of some MVFR
stratus, but most of that should be east of the forecast sites.
The weather will settle down during the morning, but daytime
heating and the approach of an upper level trough will result in
an increased risk of showers during the afternoon over central WA
shifting into eastern WA and north ID late in the day or evening.
VFR conditions are generally expected. fx
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.PRELIMINARY POINT TEMPS/POPS...
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Spokane        56  40  52  40  54  40 /  10  40  60  60  10  30
Coeur d`Alene  54  40  50  40  53  39 /  20  50  70  80  20  30
Pullman        54  38  51  42  51  37 /  30  40  60  70  20  30
Lewiston       59  44  58  45  60  47 /  40  40  50  70  20  30
Colville       53  37  51  34  54  31 /  30  60  70  60  10  30
Sandpoint      50  38  46  39  49  35 /  30  70  90 100  40  40
Kellogg        52  38  46  39  48  40 /  50  60  80 100  50  40
Moses Lake     57  42  55  40  58  40 /  20  20  50  20   0  30
Wenatchee      54  40  54  41  55  42 /  30  30  70  50  20  50
Omak           55  41  55  37  58  38 /  40  40  70  50  10  40
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.OTX WATCHES/WARNINGS/ADVISORIES...
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ID...None.
WA...Winter Weather Advisory until 5 AM PDT early this morning for
     Western Okanogan County.
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$$