Area Forecast Discussion
Issued by NWS Spokane, WA

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661
FXUS66 KOTX 201755
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1055 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.

&&

.UPDATE...
Frost advisory expired earlier this morning. Expanded a 20% chance
for showers and thunderstorms further west across the northern
mountains into the Okanogan Highlands, as well into the north
Cascades. /SVH

&&

.DISCUSSION...

Sunshine will act to warm up the surface across the northern
mountains and in the Idaho Panhandle now that the low clouds and
fog has burned off. Shower and thunderstorm coverage will be less
this afternoon with shortwave ridging of higher pressure
beginning to build in from the west into eastern Washington.
Differential heating over the higher terrain should lend to
isolated to scattered convection. Convection will be isolated in
nature over eastern Washington and scattered in nature over the
Idaho Panhandle. /SVH

&&

.PREV DISCUSSION... /issued 500 AM PDT Mon May 20 2024/

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 keepgreater thunderstorm coverage  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...
18Z TAFS: The Inland Northwest is on the back edge of an exiting
upper level trough of lower pressure. There will be enough
instability for convective showers and isolated thunderstorms to
form this afternoon. Best chances of thunderstorms are expected in
the Idaho Panhandle today with hazards that may include brief
heavy downpours, small hail, and gusty outflow winds. An isolated
cell or two cannot be ruled out over northeast Washington as well.
Skies will clear out with loss of surface heating through the
evening. A wet low pressure system will make its entrance on
Tuesday with increasing clouds expected overnight. /SVH

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Some high
resolution models show a potential for thunderstorms across
northeast Washington today similar to what happened Sunday
afternoon, so there is a 10-15% chance KGEG, KSFF, and KCOE would
have thundershowers in the vicinity between 21-02Z today. /SVH

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

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

&&

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

$$