790
FXUS66 KOTX 141128
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
428 AM PDT Wed Aug 14 2024

.SYNOPSIS...
The Inland Northwest will be between weather systems today before
the next low pressure system swings through Thursday into Friday.
Thunderstorms Thursday afternoon into Thursday night will bring
the potential for gusty outflow winds. This will be followed by
wetter showers and thunderstorms on Friday particularly across the
Idaho Panhandle and northern mountains. Daytime temperatures will
be near normal through the week.

&&

.DISCUSSION...

Today and Tonight: Low pressure will pull away from the region with
decreasing showers and clouds dissipating today over the southeast
portion of the region. Higher heights building in over the region
will result in benign weather conditions with sunny skies other
than some fair weather cumulus over the mountains by the afternoon.

Thursday through Friday night: Weather will turn unsettled again
with the next upper level low pressure system making its impact.
This low pressure system is situated out over the eastern Pacific at
around 133W/37N early this morning. It`s progged to eject
northeastward across the Inland Northwest Thursday into Thursday
night. Best dynamics looks to shift across extreme eastern
Washington and over the Idaho Panhandle. The National Blend of
Models indicates between 500-700 J/kg of surface based CAPE over the
Northeast Blue Mountains, and into the southern to central Idaho
Panhandle as the shortwave rounds into the area Thursday afternoon.
The deterministic NAM and Canadian model guidance suggest a
potential for closer to 1000 J/kg of surface based CAPE. There is
convective inhibition to contend with, but there should be enough
dynamics to overcome this. The atmosphere will be unstable out
across the Palouse, Spokane Area, and into the Upper Columbia Basin
as well, but CAPE will be weaker further out into the basin. The NAM
also indicates around 25 kts of bulk shear in the 0-6 km layer over
the Panhandle. This is marginal for seeing stronger thunderstorms.
What is potentially concerning is the amount of Downdraft CAPE (or
DCAPE). Surface temperatures Thursday will warm into the mid to
upper 80s with an inverted V model sounding profile with DCAPEs on
the order of 1000 J/kg. This combined with marginal potential for
stronger storms  moving north across the Idaho Panhandle may result
in strong outflow winds from initial developing convection. The UW-
WRF also shows this potential producing outflows from convection
across this area. Potential for stronger outflow winds will be less
over eastern Washington with instability lacking, but not completely
out of the question.

Vertical profiles moisten up through the night on Thursday night
Friday. P-Wats increase up to near an inch with showers and
thunderstorms expected to become increasingly more wet. Nocturnal
convection Thursday night looks marginal for lightning. Thunderstorms
should become less numerous heading into the midnight hour on
Thursday with precipitation potentially taking on more of a
stratiform band across the Idaho Panhandle with internal convective
elements into Friday morning. Then the question becomes how much in
the way of surface based convection do we see Friday afternoon. If
the timing is right, I believe we`ll see the atmosphere destabilize
with isolated to scattered thunderstorms developing over the
northern mountains as the deformation band clears north into Canada.
The NBM shows between 300-500 J/kg of surface based CAPE across
these northern zones for Friday afternoon. Thunderstorms will be
slow moving and contain heavy rain. Both the NAM and GFS model
sounding profiles exhibit a moist sounding through the vertical
profile. This is an indication that convection will contain the
potential for very heavy rain. Highest risk areas will extend from
the north Cascades over to the Northern Panhandle. This looks like a
good set up for flash flooding and/or debris flows, and particularly
so near burn scars and in steep terrain.

Temperatures on Friday will cool into the mid 70s to mid 80s. /SVH

Saturday through Wednesday: We will continue to live in the in
between of a low off the west coast and a ridge over the
rockies/northern plains. Saturday, 54% of the ensembles suggest
the low will be closer to the coast with a wave moving up in the
broad south to southwesterly flow aloft. Closer to the surface,
winds will become upslope into the Cascades during the afternoon
and evening hours. There is a 30-40% chance of showers for
portions of central WA with a 20-30% chance of thunderstorms.
Showers and thunderstorms could continue through the night, though
instability is pretty weak. During the late afternoon/evening
hours is the best chance in the extended forecast for portions of
eastern WA and north ID to see showers as well, tho the
probability is only about 20%.

The remainder of the forecast period has the best chance of
showers and/or thunderstorms along the Cascades and the
US/Canadian border most days. No significant concerns in the
forecast. Temperatures will be warmest Saturday, in the 80s to
around 90 which is several degrees above average, and then temps
start to cool a degree or two each day thereafter. By next
Wednesday temps will be at or a few degrees below average.

No significant wind events are being indicated in the models, but
we could see gusts Sunday onward of 15-20 mph each afternoon
and/or evening across portions of central WA onto the Palouse and
Spokane area. /Nisbet


&&

.AVIATION...
12Z TAFS: The Inland Northwest will be in between systems today.
Look for light winds and mainly clear skies east of the Cascades.
Fire activity in Washington has decreased in recent days with
several fires in the Cascades receiving some rain. If no new fires
develop, visibility should be VFR across central and eastern
Washington as well as north Idaho Wednesday and Wednesday night.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high
for VFR conditions. /GKoch

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

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        84  56  87  59  81  56 /   0   0   0  30  30  10
Coeur d`Alene  82  55  85  58  78  55 /   0   0   0  40  50  10
Pullman        80  50  81  51  78  52 /   0   0  10  40  30  10
Lewiston       89  62  88  63  86  63 /   0   0  10  50  20  10
Colville       84  46  87  47  80  45 /   0   0   0  20  40  20
Sandpoint      81  52  84  55  75  51 /   0   0  10  40  60  20
Kellogg        79  59  83  58  75  58 /   0   0  10  60  60  10
Moses Lake     86  54  87  56  84  56 /   0   0   0  20  10  10
Wenatchee      86  63  87  62  83  62 /   0   0  10  10  20  10
Omak           91  60  92  61  87  59 /   0   0   0  10  40  20

&&

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

$$