Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 261156
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
456 AM PDT Tue Oct 26 2021

.SYNOPSIS...
Breezy winds and rounds of rain and mountain snow will continue
this week across the Inland Northwest. The north Cascades will
likely receive several rounds of accumulating snow in the high
terrain. Tuesday and Wednesday will be windy across the Waterville
Plateau, Columbia Basin, Palouse, and West Plains with gusts of
30 to 40 mph. Moderate precipitation and strong winds are likely
Thursday into Friday. Small rises on many rivers and streams are
expected into the weekend.

&&

.DISCUSSION...

...ISOLATED STRONG WIND GUSTS EARLY WEDNESDAY MORNING...

Tuesday and Wednesday: A ridge high pressure will build in from
the south pushing the current trough of lower pressure to the
east. As this transition is occurring, the jet stream will migrate
across the Inland NW leading to a couple of windy days. The
transition will also bring several more rounds of precipitation
largely in the form of rain and high mountain snow. Temperatures
will remain seasonal each afternoon with highs in the 50s while
overnight lows for most lowlands remain warmer than average
bottoming out in the upper 30s to 40s.

* Winds: Winds this afternoon (TUE) will be from the
 south/southwest featuring sustained speeds of 10-20 mph and gusts
 25-35 mph. Windiest locations will be across the Palouse, West
 Plains, Columbia Basin, and into the Okanogan Valley. Impacts
 from these winds should be minor to none. A stronger jet passes
 over the region overnight into Wednesday morning, between 11PM-
 8AM. 500mb during this time will be just shy of 100kts which is
 quite impressive and climatologically very rare. Luckily, these
 intense winds will be well off the surface, blowing at an
 elevation roughly 20,000 feet above ground level. Closer to the
 ground level, we do anticipate a jet around 45kts to bring the
 potential for wind gusts between 40-45 mph for portions of the
 Columbia Basin and 50-60 mph on exposed ridgetops in the Cascades
 and Blue Mountains. The Waterville Plateau will carry the
 greatest risk for gusts around 45 mph early Wednesday morning
 however, several of the hi-res models continue to forecast wind
 gusts 40-45 mph (briefly) on the higher benches of the eastern
 Basin including the West Plains, South Hill, and Palouse.
 Sustained winds at this time look to remain in that 15-20 mph
 range. Wind direction during this time of potentially stronger
 gusts will be from the west/southwest which suggest a good deal
 of sheltering for our northern mountain valleys and little
 concern. Potential impacts from the nocturnal winds include
 isolated tree damage and power outages. The jet will weaken
 slowly through the day Wednesday but be prepared for another
 windy day with sustained speeds of 10-20 mph and gusts to 35 mph.
 Wind direction for Wednesday will be from the west and
 southwest. Little to no impacts are expected Wednesday afternoon.

* Rain: Light scattered showers drifting across the region this
 morning. A more organized band of rain is expected to pass
 through this afternoon reaching Wenatchee and Moses Lake around
 midday then Northeast Mountains, Spokane Area, and Palouse this
 afternoon near 1-3PM. As this band exits to the east this
 evening...additional showers will be possible just about
 anywhere. By the overnight hours, most showers will retreat to
 the Cascade Crest and Idaho Panhandle as increasing westerly flow
 creates a large rain shadow in the lee of the Cascades. Clouds
 will increase on Wednesday but away from the Cascade Crest,
 Wednesday looks to feature mostly dry conditions for much of
 Eastern WA and N ID.

*Snow: A barrage of showers under the swift westerly flow Tuesday
 night will bring the potential for snow showers over the Cascade
 Crest. Snow levels look too high for any concerns at Stevens
 Pass at this time however Washington Pass could pick up 3-6
 inches of new snow by Wednesday morning.

...WINDY & MODERATE TO HEAVY RAINFALL THURSDAY INTO FRIDAY...

Wednesday night through Thursday night: Precipitation chances
will ramp up in this time-frame as a moisture laden warm front
ushers a weak to moderate atmospheric river into the Pac NW. This
has been well agreed upon over the last few days of model runs
with the main uncertainty associated with the track and speed of
the offshore low. Models appear to be coming into better agreement
and confidence is increasing that the warm front will swiftly
move northward into southern BC Thursday focusing the heaviest
precipitation over the Northern Cascades and mountains near the
Canadian Border Thursday before retreating southward back into our
region Thursday night. QPF amounts for the North Cascades and
Idaho Panhandle could be measured in inches. Initially this will
fall as snow for elevations above 5000 feet Wednesday night and
Thursday morning but snow levels will rise Thursday afternoon
above most of our mountain peaks. Washington Pass could receive a
period of heavy snow before this occurs and winter travel
conditions should be anticipated Wednesday night into Thursday
morning. Light to moderate precipitation amounts are also
expected for the Northeast Mountains, Okanogan Highlands, and
portions of the Eastern Columbia Basin. A healthy rain shadow is
expected in the lee of the Cascades. Rainfall amounts for these
areas will range from 0.25-0.80" with locally higher amounts for
the 36 hour period.

It will likely be another windy day on Thursday and could prove
to be one of the strongest wind events this week. Ensemble models
are trending in this direction and suggest the potential for
southwest winds across the Basin at sustained speeds of 15-25 mph
coupled with gusts near 40 mph. All things considered, this is
welcome rainfall for our drought stricken area but some of our
sensitive areas in the Cascades, NE WA, and N ID will need to be
monitored closely for heavy rain rates and potential for rock and
mud slides.  Some of our rivers and streams will also see rises.
/sb

Friday through Monday:
Chances for showers will linger into Friday as a cold front pushes
through the Inland Northwest. After this passage, we`ll shift to
drier conditions for Saturday through Monday, along with daytime
temps that have cooled back down to seasonal norms. With the drier
weather in place, we will also experience overnight lows dropping
below freezing for many locations. /KD

&&

.AVIATION...
12z TAFS: Southwest directed into the rising terrain of NE WA and
N ID will keep a threat for MVFR stratus around Coeur D Alene,
Bonners Ferry, Colville, and Spokane through this morning. A band
of light rain is expected to track across the forecast area
between 19-00z. Brief MVFR cigs are possible with this band and
for a few hours behind it but confidence is low given gusty winds
developing through the day. Winds will become the main concern for
the overnight hours as a strong jet noses into the forecast area.
Wind gusts around 40 mph will be possible on the higher benches
around the Spokane, Coeur D Alene, Kellogg, Pullman, Lewiston, and
across the Basin into the East Slopes of the Cascades including
Chelan and Wenatchee. Winds to remained decoupled from the surface
in the lee of the Cascades and around Wenatchee until closer to
12z so did introduce LLWS./sb

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        52  40  53  43  59  47 /  80  50  10  40  50  40
Coeur d`Alene  49  39  51  42  56  46 /  80  70  20  40  60  50
Pullman        52  40  51  43  60  45 /  70  70  10  40  40  30
Lewiston       60  46  60  47  68  51 /  60  70  10  30  30  30
Colville       51  35  53  40  52  41 /  80  60  10  50  60  60
Sandpoint      46  39  48  39  49  43 /  90 100  30  50  80  70
Kellogg        47  38  47  39  54  45 /  90  90  50  50  70  50
Moses Lake     55  40  57  45  61  47 /  70  10   0  40  30  30
Wenatchee      54  41  55  41  57  45 /  80  50  10  60  50  50
Omak           54  37  56  39  54  41 /  80  40   0  50  60  50

&&

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

&&

$$


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