187
FXUS66 KOTX 252328
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
428 PM PDT Sat May 25 2024

.SYNOPSIS...
Showers will continue across the Inland Northwest through
sunset. Breezy to windy west to southwest wind gusts of 25 to 35
mph will continue through the evening across central Washington.
Dry weather returns on Sunday and Monday with temperatures warming
back into 70s and 80s. A return of wet weather is expected to
return Tuesday onward, with temperatures trending cooler.

&&

.DISCUSSION...
Tonight: A weather disturbance is moving across southern British
Columbia producing scattered showers across northern WA and the
ID Panhandle this afternoon. Showers will continue through the
evening hours. There is a 20-30 percent chance of thunderstorms
through sunset mainly along the Canadian border. The pressure
gradient from Seattle to Wenatchee is currently 7.8mb and will
continue to be near that value through the afternoon before the
gradient begins to relax around sunset. Windy conditions will
occur across the Cascade gaps onto the Waterville Plateau and
Columbia Basin. The NBM is showing a 30 to 50% chance of gusts to
30 mph for the Columbia Basin and Wenatchee area. Probabilities
are higher- 60-75% chance for the Waterville Plateau and northern
Grant county.

Clouds will partially thin and/or dissipate overnight. Some of the
colder valleys could see some frost. Main areas of concern are NE
WA and north Idaho, like around Colville, Priest Lake, Republic
and Deer Park. Probabilities of frost for these locations is
45-60%. NBM is also showing lower probabilities of 15-20% around
Spirit Lake/Athol, Wilbur/Davenport, Moscow/Troy areas.

Sunday and Sunday Night: The weather disturbance will move over
the Continental divide and a broad ridge will begin to set up
across the region. There is still a 20-25% chance of showers in
the afternoon right along the Canadian border. Instability is not
as strong, so no thunderstorms in the forecast. Winds will be
lighter and temperatures will be a couple of degrees warmer. The
afternoon will see partly to mostly cloudy skies. Temperatures
Sunday night/Monday morning will be warmer than the previous day
as the ridge builds in and there will be more cloud cover. /Nisbet

Monday to Saturday: High pressure will keep the area dry and mild
Monday, before a cold front moves in with rain and t-storm
chances, increased winds and a cooling trend; by late week the
shower chance retreat to the mountains. First on Monday the ridge
axis will shift toward the northern Rockies. This will leave the
area in a mild southwest flow and high clouds spilling in ahead of
the next system and some afternoon cumulus build-ups,
particularly around the mountains. Highs are forecast to be in the
70s, with some low 80s in the deeper basin and L-C valley.

Then Monday night and Tuesday impulses start to ride in ahead of
the approaching cold front. Overnight into early Tuesday this will
bring an increase in clouds, with limited shower chances coming
onto the Cascade crest and the Blue Mountains to southern
Palouse/lower ID Panhandle. Ensembles show about a 20-40% chance
of measurable precipitation (>=0.01 inches) in these areas, so I
raised PoPs here slightly compared to the NBM. Some guidance
expands that risk a bit further northeast toward the Spokane/CdA
area before sunrise but confidence is too low (less than 10%) to
add to the forecast.

Heading into Tuesday through Tuesday night precipitation chances
expand over much of the region as the cold front and upper trough
push in, drawing on deeper moisture and instability. The highest
will be in the afternoon and evening over the southeast WA through
the central Panhandle. The lowest risk will be over the lower lee
of the Cascades and deeper Columbia Basin. Accompanying the
general precipitation threat will be thunderstorm chances, with
models painting the best instability over southeast WA through the
central Panhandle. SBCAPE values could between 100-800 J/kg.
However models are not in great agreement yet over where the
better instability will lay. Still there is decent 0-6KM shear at
40-50kts and PWATs rising to around 0.70 to 1.0 inches (150-170%
of normal). So locally heavier rain and strong t-storms will be
possible, especially in these area, with gusty winds and hail. We
will have to watch for localized hydrology issues such as ponding
of water or debris flow/rock slides. The River Forecast Center
does show some rises on mainstem river, but all of them are
currently forecast to stay below action stage. However we will
have keep eye on smaller creeks and streams.

By Wednesday the area will be dominated by long-wave trough with
a second upper shortwave coming into the region in the afternoon
evening. This will continue precipitation chances through much of
the region. but by this time drier air infiltrates the region,
with PWAT decreasing to around 0.25 to 0.45 inches (70-80-% of
normal). Unstable lapses rates and bit of SBCAPE remains over the
region. So showers will be possible, with embedded t-storm
chances. The potential for stronger storms will be lower, with
less instability and overall less shear. But some isolated
stronger storms are not out of the question over the SE CWA.

Expect breezy winds to develop for Tuesday and Wednesday,
especially near the Cascades into central WA. Gusts of 15-35 mph
in the afternoon and evening hours, with that higher range closer
to the Cascades.

Thursday to Saturday the upper trough gradually shifts east while
a ridge starts to build in from the west (ahead of another system
that approaches toward the latter part of next weekend). How
quickly all this occurs is not agreed on. Shower chances will
continue around the mountains through this period, expanding to
include the eastern third of WA Thursday afternoon under the still
exiting trough.

Temperatures will be above normal Monday and Tuesday, though
temperatures Tuesday could be held back in the clouds and
precipitation are more dominant the forecast. Expect cooler than
normal conditions on Wednesday and Thursday, then a return to
slightly above normal temperatures. /Solveig


&&

.AVIATION...
00Z TAFS: VFR conditions for TAF sites. Gusty winds will continue
across the Basin and Palouse with GEG/PUW/LWS/MWH/EAT seeing
gusts 25-35 kts through the evening. Confidence has lowered for afternoon
isolated thunderstorms for Northeast Washington and North Idaho
impacting K63S-KSZT-K65S, but scattered showers will continue to
push east through the evening.


FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Confidence is high for the winds but low for the thunderstorms.
Confidence is higher further north for shower development, toward
the Canadian border.

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

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        40  65  44  73  51  75 /  10   0   0   0   0  20
Coeur d`Alene  39  62  45  72  50  73 /  30   0   0   0   0  30
Pullman        38  62  43  71  50  73 /  10   0   0   0  10  20
Lewiston       44  71  49  81  57  81 /  10   0   0   0  10  20
Colville       34  65  38  72  43  73 /  40  10   0   0   0  40
Sandpoint      39  61  44  70  48  71 /  50  10  10   0   0  50
Kellogg        41  58  44  71  52  74 /  30  10   0   0  10  40
Moses Lake     41  72  44  78  52  78 /   0   0   0   0   0   0
Wenatchee      46  68  47  76  55  73 /  10   0   0   0   0  10
Omak           40  71  44  75  50  75 /  10  10   0   0   0  20

&&

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

$$