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000
FXUS66 KOTX 161733
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1033 AM PDT Tue Apr 16 2024

.SYNOPSIS...
Anticipate cool, brisk, and somewhat showery weather as a low
pressure system aloft drops over the Inland NW and lingers
through Thursday. It will be chilly early in the morning with lows
dipping below freezing for many areas and the threat of frost.
The weather gradually warms and dries by Friday into the weekend
and continues into early next week with above normal temperatures.


&&

.DISCUSSION...
Today and Tonight: The arrival of a closed upper level low from
the north will bring cool and unsettled weather to the region.
The band of high level clouds that spans across eastern WA early
this morning is expected to slowly push southeast in advance of
the closed circulation. Some sporadic wind gusts still seen over
parts of Grant county in the Basin, although should gradually
decrease this morning.  The clearing will be short lived this
morning as cumulus will bubble across the mountains and spread
across the lowlands by afternoon.  The best chances will be across
the northern and Panhandle mountains by afternoon. Surface based
instability increases with skinny wedges of cape to 120 J/kg over
the northern tip of the ID Panhandle with a 5% of a thunderstorm.
Most convection will be snow or graupel showers based the cold
-35C at 500mb with the area of low pressure.

Anticipate a return of the westerly gusty winds by afternoon but
weaker than yesterday, spanning from the lee of the central
Cascades across the Columbia Basin with gusts 25 mph. Winds shift
from the north overnight and remain brisk across central WA,
especially funneling down the Okanogan Valley, across the
Waterville Plateau into the western Columbia Basin. Daytime
temperatures will be noticeable cooler, by about 10 degrees
compared to Monday. Meanwhile, lows tonight will dip into the 30s
with many areas experiencing near freezing temperatures. After the
mild temperatures lately, this may be concern for those who have
done early planting. Areas of frost may be seen in many lowland
areas where the winds decouple across extreme eastern WA.
Climatologically, the growing season has just started for the LC
Valley, Moses Lake area, and Wenatchee area, and these areas are
expected to see the least threat of frost.

Wednesday and Wednesday night: Cool conditions continue as the
upper level circulation gradually weakens and shifts east, leaving
a northerly flow aloft across the region. Chilly morning
temperatures and areas of frost will be a concern early in the
morning for parts of eastern WA. Brisk northerly winds will
persist through the day in central WA with gusts of 25 to 30 mph.
Cumulus buildups return for the mountains with showers bubbling up
by afternoon, especially for northeast WA and the ID Panhandle in
the form of snow or graupel showers. Instability increases by
afternoon but remains weak and spotty. Winds decrease gradually
overnight while temperatures dip back into the 30s with the threat
of frost and freezing temperatures especially in sheltered low
lands. /rfox.

Thursday through Monday: Upper level longwave ridge is pinched up
and rather narrow off the coast as an disturbances and frontal
boundaries rotate counter clockwise along an upper level low moving
slowly east along the US and Canadian border. The northerly flow on
the east side of the ridge still still allows for some upper level
instability and potential for weak disturbances and orographics to
allow for minor pops for light rain and snow showers to linger
mainly over North Idaho Thursday followed up with a dry Friday.
Ensembles still suggest a negatively tilted trof passage sometime
over the weekend thus increasing clouds and a mention of showers as
early as Saturday evening and possibly lingering on Sunday as the
upper level ridging is rather flat and more zonal. Low amplitude
shortwave ridging Monday confines any mention of showers to small
portions of the Cascade Crest and very small portions of North
Idaho. The below normal forecast temperatures continue a gradual
warming trend through Monday with some areas of frost mentioned in
spots on through the remainder of the workweek and first half of the
weekend.  /Pelatti

&&

.AVIATION...
18Z TAFS: Afternoon heating combined with cooling aloft will
destablize the atmosphere through the afternoon over the northern
mountains surrounding Winthrop, Colville, Republic, Sandpoint, and
Bonners Ferry. Yet with a dry boundary layer showers that develop
are expected to be isolated to scattered in nature. Given the
higher cloud bases and mainly light intensity to the showers CIGS
will remain VFR, except under localized moderate showers where
snow or graupel could reduce visibility to MVFR. As the cold pool
tracks into the Spokane/Coeur d`Alene area between 1-4z there is a
20-30% chance of a brief shower impacting these TAF sites.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high
confidence in VFR conditions through the TAF period, with one
exception. As the atmosphere destabilizes this afternoon into the
early evening, the HREF shows near a 10-20% chance of visibilities
dropping to MVFR under moderate showers consisting of snow or
graupel. JW

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

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

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https://www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        52  31  54  32  54  32 /   0  10  10   0  10   0
Coeur d`Alene  50  31  52  31  52  30 /  20  20  10  10  10   0
Pullman        47  30  50  30  54  31 /  10   0  10  10  10   0
Lewiston       56  36  57  36  60  36 /   0   0  10   0  10   0
Colville       53  31  55  29  54  29 /  10  10  30  10  10   0
Sandpoint      50  33  50  32  49  29 /  40  30  20  20  20   0
Kellogg        45  33  48  32  50  30 /  30  20  30  10  20   0
Moses Lake     57  33  61  36  62  37 /   0   0   0   0   0   0
Wenatchee      54  36  58  39  59  38 /   0   0   0   0   0   0
Omak           56  36  60  34  60  34 /  30  20  10   0   0   0

&&

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

$$