379
FXUS66 KOTX 280959
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
259 AM PDT Tue May 28 2024

.SYNOPSIS...
A return of showers and thunderstorms today with a cold front
passage. A few storms could be strong with gusty outflow winds in
southeastern Washington and the Idaho Panhandle. Frosty conditions
is expected Wednesday night into Thursday morning. Cool and
showery conditions will continue through the end of the week with
drier and temperatures warming back up to near normal for the
start of the weekend.

&&

.DISCUSSION...

Today and Tonight: A cold front will push into the Inland Northwest
today. The front is just off the coast and will push east of the
Cascades this afternoon. There is weak instability at mid levels
east of a line from Moses Lake to Omak. Radar is picking up on
isolated convection across much of this area including into the
Idaho Panhandle. Axis of best mid level instability with most
unstable CAPEs of 200-300 J/kg is located from Ritzville to Coeur
d`Alene. This will remain as an area for the best chances (up to
20%) for isolated thunderstorms into the early morning hours. CAPEs
will then be retard to around 100 J/kg after 8AM or so this morning
as mixing occurs in the boundary layer and the drier sub-cloud air
entrain into the moisture at mid levels. There will still be the
potential for isolated cloud to ground lightning strikes across
much of the eastern half of the forecast area into the afternoon.
Much of this convection will remain elevated. Best potential for
surface based convection will be over the far southeast portion of
the forecast area: essentially over the Northeast Blue Mountains,
Camas Prairie and southern to central Idaho Panhandle. Higher
clouds will be thickening up through the afternoon further
northwest, which will decrease the potential for surface based
convection to initiate and remain capped. This area where we may
see surface based convection and points southeastward will be the
area to watch for stronger thunderstorm development. CAPE values
of 500-800 J/kg and shear values of around 40 kts up to 6 km will
support the potential for stronger thunderstorms to develop. Main
hazard will be for damaging wind gusts from convection. Could
also see penny to nickle sized hail, but severe hail is less
likely due to higher LCLs of 8 kft and higher and a drier sub-
cloud layer. This direr air will result in evaporative cooling
that will strengthen cold pools and increase the potential for
damaging wind gusts. Instability may be limited though and may not
be enough for strong to sever thunderstorms to develop this far
northwest. Better chances will be south and east of the Lewiston-
Clarkston Valley.

Today will be a breezy day through the Cascades and out over the
exposed areas of the Columbia Basin. Expect westerly winds to
increase this afternoon with gusts in the range of 25-35 mph absent
of convective showers and/or thunderstorms.

Wednesday and Wednesday night: The upper level trough of lower
pressure will move in over the Inland Northwest with a cold pool of
minus 28 degrees Celsius over the northern half of forecast area.
Showers with embedded thunderstorms are expected to develop under
this cold pool with diurnal heating. Shear will be absent where
convection is most likely tomorrow. Much less likely for
thunderstorms to become strong and will be of the garden variety
pulse type storms. There will be a lot of dry air that pushes in
behind the cold front passage today. The drying of the boundary
layer will make it more difficult for convection to develop in
the Columbia Basin. The northern mountains of eastern Washington
and the Idaho Panhandle will see the best potential for showers up
to 40- 70%. Wednesday will see a drop in temperatures from the
70s today to the upper 50s and low 60s by tomorrow. Skies look to
clear out Wednesday night with winds weakening. This will result
in strong radiational cooling with dew points falling into the
upper 20s. Temperatures will be chilly by Thursday morning with
widespread frost conditions possible, especially in the sheltered
mountain valleys. We will have to consider frost/freeze messaging
for this period. Anyone with sensitive vegetation should consider
covering their plants to protect them from frost/freeze damage.
/SVH

Thursday through Monday: Generally dry conditions are forecast for
Thursday and Friday in the wake of Wednesday`s trough passage. And
while Thursday will be a bit cooler than normal, temperatures look
to rebound back to seasonal norms for the rest of the extended
forecast. Moderate uncertainty does remain for the weekend into
early next week, but we are anticipating increasing chances for
showers, especially by Monday. Occasionally breezy winds are also
expected each day, though any gusts are currently looking to remain
below 30 mph. /KD

&&

.AVIATION...
06Z TAFS: A weather system will spread an increase chance for
showers and thunderstorms mainly east of a line from Moses Lake to
Republic into Tuesday. Elevated instability will help contribute
to showers developing between 9-18z mainly from the Tri Cities
area up through the Columbia Basin and NE Washington. There is a
20% chance of thunderstorms at KGEG/KSFF with this round of
convection, and a 10% chance at KMWH/KPUW/KLWS. Stronger storms
are possible Tuesday afternoon and evening, but confidence is low
on whether or not any of the TAF sites will be impacted. The most
likely areas are KGEG/KSFF/KCOE/KLWS with a 30% chance of
thunderstorms. The best chances will be over far NE WA/N Idaho
with a 40-50% chance at Colville, Sandpoint, and Bonners Ferry.
Locations south and east of Lewiston will also carry a 40-50%
chance of thunderstorms. A few strong storms are possible, but
none of the CAM`s models are showing strong convective gusts
impacting any of the TAF sites.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is high confidence for VFR conditions to continue across the
region. The one exception is under heavier showers or
thunderstorms where there is a moderate chance of visibility being
reduced to MVFR. 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        73  42  59  36  65  42 /  30  10  20  10   0   0
Coeur d`Alene  73  43  57  37  63  41 /  40  30  40  30   0   0
Pullman        71  42  56  36  61  41 /  20  40  10  20   0   0
Lewiston       79  50  66  44  71  48 /  30  50  10  10   0   0
Colville       71  37  58  34  65  35 /  50  40  60  20   0   0
Sandpoint      71  43  57  34  61  39 /  50  60  70  40  10   0
Kellogg        74  45  54  41  59  42 /  30  60  40  40   0   0
Moses Lake     77  42  66  39  72  42 /  20   0  10   0   0   0
Wenatchee      72  45  64  42  69  45 /  10   0  10   0   0   0
Omak           76  41  64  37  70  42 /  20  10  10   0   0   0

&&

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

$$