672
FXUS66 KOTX 201200
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
500 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 /12Z MONDAY THROUGH FRIDAY/...
06Z TAFS: Shallow valley fog will begin to dissipate after
sunrise Monday morning in mountain valleys of northeast
Washington and the Idaho Panhandle. KGEG, KSFF and KCOE are the
sites impacted by valley fog with highly variable VSBY from
1/2SM to 6SM. This will be short lived as the sun warms the
ground after sunrise. Showers with isolated thunderstorms will
mainly be confined to extreme eastern Washington and the Idaho
Panhandle for Monday afternoon. TAF KCOE is the only TAF with
-TSRA forecast after 21Z.  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:  Some high
resolution models show greater thunderstorm coverage into
east-central Washington Monday similar to what happened Sunday
afternoon so there is a 10% chance KGEG and KSFF would have
thundershowers in the vicinity. TC

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

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        42  63  45  54  42  64 /  10  20  80  90  50  30
Coeur d`Alene  41  62  45  52  42  62 /  20  20  90 100  60  40
Pullman        39  61  44  51  40  58 /  10  10  80  90  60  40
Lewiston       45  70  50  59  46  65 /   0  10  80  90  60  40
Colville       37  63  40  54  38  66 /  10  30  80 100  50  40
Sandpoint      40  61  45  51  42  61 /  30  20  90 100  60  50
Kellogg        42  60  46  49  43  58 /  40  20  80 100  80  60
Moses Lake     43  67  45  59  44  72 /   0  20  20  60  20  10
Wenatchee      48  65  46  59  46  71 /   0  30  20  50  10   0
Omak           44  65  45  59  43  73 /  10  30  50  70  20  10

&&

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

&&

$$