517
FXUS66 KOTX 200957
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
257 AM PDT Mon May 20 2024

.SYNOPSIS...
There will be a brief break between weather systems Monday into
Tuesday. Then a wet low pressure system is expected late Tuesday
and Wednesday, lingering Thursday. Another weather system will
move in on Friday. The week and into the Memorial Day weekend will
be cool, unsettled with thunderstorms each day, especially over
the higher terrain.

&&

.DISCUSSION...
Today:
Skies have been clearing overnight with some lingering clouds
from Pullman Washington into the Lewiston/Clarkston valley.
Clearing skies helped promote some patchy fog from North Spokane
Mead and Dartford areas to around Deer Park. Temperatures around
Deer Park are near freezing so local roadways may be slick
during the morning commute. The fog is fairly shallow so it
should dissipate fairly quickly after sunset. The frost advisory
goes until 8 am this morning and looks good from that
perspective.

* More Thunderstorm Potential Today:
We`ll be looking for additional cloud buildups today with a
slight chance of thunderstorms similar to but not as far quite
as far west as yesterday. Stevens and Pend Orielle county of
Washington and the north Idaho have enough potential
instability to support showers turning into a few lightning
strikes this afternoon. Storm track will be northwest to
southeast which is similar to yesterday. With high pressure
building in from the west this should cap thunderstorm
convection any further west but mountain showers in north
central WA will still pop up as well. Wind gusts to 30 mph with
pea sized hail and lightning are still the main threats going
into the afternoon and early evening hours.


Tonight through Tuesday: After early evening convection winds
down we`ll have brief high pressure building over the Inland
Northwest. High clouds coming in ahead of the next weather
system will keep temperatures a bit warmer than the last few
days for reduced frosting potential. Northern valleys still will
dip down to around 36 degrees at Republic and Deer park though
but these are typically cooler spots.

Clouds continue to increase Tuesday with light rain across the
region into the Idaho Panhandle by around noon. TC

Tuesday Night and Wednesday: An upper level low pressure system
will approach the region from the northwest Tuesday afternoon and
by the evening precipitation will be spreading across the region.
Nearly every location will see precipitation from this weather
system Tuesday Night and Wednesday. Ensemble guidance suggest
probabilities of a quarter inch or more of rain for portions of
central WA range from 10% around Wenatchee to 25% around Moses
Lake to around 50% across the northern Waterville Plateau. There
is a 50-65% probability across north central WA and into the
Spokane area and down to the Palouse and LC Valley. As you head
into northeast WA and the ID Panhandle, probabilities go up to 80%
or higher. Portions of the ID Panhandle could see upwards of
three quarters of an inch with this midweek system.

Snow levels will lower to 4000-4500 ft Wednesday morning. Snow may
briefly mix in at Stevens Pass with little to no accumulation.
Washington Pass will see snow accumulation, with a 50% chance of
an inch, and a 30% chance of 2 inches.

As the low moves into the area Wednesday there is enough
instability for a 20% chance of thunderstorms in the afternoon
across portions of eastern WA and the entire ID Panhandle.

Thursday through Memorial Day: The trough moves over the Divide
and precipitation chances lower. However, afternoon showers and
thunderstorms are possible across northeast WA and the ID
Panhandle.

Friday another low pressure system moves into the region. Showers
and thunderstorms remain in the forecast. Instability looks a bit
better Friday compared to Wednesday. Saturday the low exits the
region into Montana, and we remain cool and unsettled with
showers and thunderstorms. Sunday 45% of the ensembles show a
ridge of some kind over the Inland Northwest, with 55% keeping it
more troughy. Finally by Monday there appears to be better
agreement of the ridge setting up, just in time to finish your
Memorial Day weekend drier with warmer temperatures. /Nisbet

&&

.AVIATION...
06Z TAFS: Patchy fog or low stratus will be possible Monday
morning in mountain valleys of northeast Washington and the Idaho
Panhandle. Showers with isolated thunderstorms will mainly be
confined to extreme eastern Washington and the Idaho Panhandle for
Monday afternoon. Hazards include infrequent lightning, brief
heavy downpours, pea sized hail, and gusty erratic winds up to
25-30 kts with stronger thunderstorms.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There`s a 15%
chance for low stratus producing MVFR conditions along the
Spokane-Coeur d`Alene corridor Monday morning. This will be
dependent on additional rain that this evening that moistens the
boundary layer. Some high resolution models show greater storm
coverage into central Washington Monday similar to what happened
this afternoon.

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

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        67  42  63  45  54  42 /  10  10  20  80  90  50
Coeur d`Alene  65  41  62  45  52  42 /  30  20  20  90 100  60
Pullman        62  39  61  44  51  40 /  10  10  10  80  90  60
Lewiston       70  45  70  50  59  46 /  10   0  10  80  90  60
Colville       69  37  63  40  54  38 /  10  10  30  80 100  50
Sandpoint      62  40  61  45  51  42 /  40  30  20  90 100  60
Kellogg        60  42  60  46  49  43 /  30  40  20  80 100  80
Moses Lake     74  43  67  45  59  44 /   0   0  20  20  60  20
Wenatchee      72  48  64  47  59  46 /   0   0  30  20  40  10
Omak           74  44  65  45  59  43 /   0  10  30  50  70  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Frost Advisory until 8 AM PDT this morning for Northeast
     Mountains-Okanogan Highlands-Upper Columbia Basin.

&&

$$