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000
FXUS66 KOTX 251153
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
453 AM PDT Thu Apr 25 2024

.SYNOPSIS...
Light rain will spread into the Inland Northwest this afternoon
and evening. More seasonal temperatures are expected Friday into
the weekend with on and off showers and a few weak thunderstorms.
Unsettled conditions continue into next week.

&&

.DISCUSSION...
Today through Saturday:  A shift in the weather pattern is ongoing
this morning with a transition from warm and dry conditions
toward seasonal and unsettled. A weak cold front that moved
through on Wednesday was the initial blow to the upper ridge with
mean upper-level troughing now established. A stronger shortwave
that is evident on the water vapor along 130W will enter the PacNW
today and depart on Friday. This system has a deeper axis of
moisture to work with with PWATS increasing closer to three-
quarters of an inch or 180% of normal for this date. However, the
best dynamics will split around the Inland Northwest.
Additionally, some of the moisture will be reserved to saturate an
antecedent sfc-700mb dry layer. Nonetheless, widespread light
rain will spread from west to east through the afternoon and
evening. Rainfall amounts through Friday morning will be light
with less than a tenth in the Basin and between a tenth to quarter
of an inch in northern mountains and Idaho Panhandle. The
mountain valleys could be closer to a tenth or less. HREF supports
this notion with 5-15% chance for a tenth in the Basin and
60-100% chance northern mountains and Idaho Panhandle. The system,
lacking strong westerly flow, should deliver a few hours of light
rain to all locations including the lee of the Cascades. This
will not be a very cold system allowing temperatures on Thursday
to sneak into the low 60s and upper 50s.

Steady rain will transition to showers on Friday afternoon.  Breaks
in the clouds will result in mediocre CAPE in the afternoon and
convective showers and few weak thunderstorms. There is 20-40% for
200 J/kg; 15% chance for 300 J/kg; and 0% chance for CAPES of 400
J/kg. 500mb temperatures only cool near -24C which is not overly
impressive. Cells will mainly produce brief downpours and
potential for infrequent lightning strikes. At this time, the
highest probability for lightning will be in two areas: 1) across
the northern mountains (roughly between Hwy 2 and the Canadian
Border) and 2) across the far southeast (Blue Mountains, Camas
Prairie, L-C Valley, and Palouse). A lot will be dependent on
where the best breaks in the clouds occur. Rainfall amounts Friday
afternoon will vary from one location to another given the
showery nature but generally around a tenth or less outside
thunderstorm cores. Temperatures on Friday will remain in the
upper 50s to lower 60s.

Another ripple in the flow will arrive on Saturday.  At this time,
500 mb temperatures warm a few degrees and mid-level westerly
flow becomes a bit stronger. As the next wave comes through,
another band of showers or clouds will accompany the midlevel
front with light showers. There should be more shadowing in the
lee of the Cascades with this wave keeping the highest shower
chances across Idaho and the eastern third of WA as well as the
Cascade Crest. A few weak thunderstorms will be possible (15%
chance) over Northeastern WA and far North Idaho. Rainfall amounts
will be less than a tenth of an inch outside any t-storm cores.
South to southwest winds do increase with speeds near 10-15 mph
within the Okanogan Valley and Columbia Basin gusting near 25 mph
at times. Temperatures warm a degree or two with readings in the
mid to low 60s. /sb

Sunday through Thursday: There is high confidence for unsettled
conditions to continue into next week. A deep low off the BC
coast Sunday will keep precip chances around for Sunday with west-
southwest flow into eastern WA and north Idaho. 850 mb
temperatures in the Cascades cool enough to support snowfall by
Sunday evening with a frontal passage (80% of the global ensemble
colder than -1C). There is a 70% chance of 3 inches of snow or
more Sunday evening through Monday night at Stevens Pass (25% at
the recently opened Washington Pass).

There is a brief window where a couple snowflakes are possible in
the eastern third of WA and north Idaho Monday morning with a 40%
chance of 850 mb temperatures colder than -1C. However, the shadow
effect will prevent significant precipitation accumulation east of
the Cascades next week. With the front passage Sunday afternoon,
there is a 20-40% chance of wind gusts 35 mph or greater, raising
blowing dust concerns in the Basin and Waterville Plateau. Winds
remain elevated Monday as the PDX-GPI pressure gradient is modeled
around 12 mb with similar probabilities of wind gusts 35 mph or
greater.

The parent trough stays off the BC coast through at least Wednesday
and starts to migrate inland Thursday. Thus, the cooler and moist
pattern remains through late week. /Butler

&&

.AVIATION...
12Z TAFS: A front passing through the region will increase chances
for precipitation later this morning in central WA and this
afternoon in eastern WA and north ID. Light rain is expected
across all airports with the potential for MVFR conditions into
the evening and overnight hours.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate
confidence in MVFR cigs around 01-06z light rain band.
-----------------------

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        60  44  58  42  61  42 /  30  80  60  20  30  20
Coeur d`Alene  58  44  54  41  59  42 /  30  90  70  30  50  30
Pullman        58  43  56  40  57  40 /  20  90  60  30  30  20
Lewiston       66  48  62  46  64  45 /  20  80  60  20  20  20
Colville       61  43  57  39  61  37 /  40  90  90  50  70  40
Sandpoint      55  44  53  41  56  42 /  40  90  90  50  80  50
Kellogg        55  43  51  43  55  43 /  40  90  90  50  80  50
Moses Lake     63  43  65  42  67  40 /  50  40  20  10  10   0
Wenatchee      60  45  62  44  64  43 /  70  40  30  10  10   0
Omak           63  45  62  44  66  41 /  60  80  60  30  20  10

&&

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

$$