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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KOTX 141043
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
343 AM PDT Sun Apr 14 2024

.SYNOPSIS...
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Expect an unseasonably warm day across the Inland Northwest. High
temperatures will generally be more typical for what we would
expect to see in mid June. Most locations will be dry, however
there will be a small chance of showers and thunderstorms over
extreme southeast Washington and the southern half of the Idaho
Panhandle on Sunday afternoon and night. A cold front will bring a
return of cooler, showery weather early next week. The front will
bring breezy conditions Sunday night through Monday.
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&&

.DISCUSSION...

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Today...A strong upper level low, currently just west of the Bay
Area, will push inland today in response to shortwave trough
currently poised off the northern BC coast. So what will that do
to our weather today? The most noteworthy aspect to our weather
will be an unusually mild day for mid-April. 850 mb temperatures
yesterday ranged from approximately 10-12C across eastern
Washington and north Idaho and confidence is high we should add a
couple degrees to that. That translates to high temperatures in
the 70s for most locations with a few possibly touching 80
degrees. These values are comparable to the average highs in mid-
June. The NBM probabilities of exceeding 80 are around 80% for
Moses Lake and Othello, 70% chance for Omak, a 40% for Lewiston
and the LC Valley. Even Spokane Valley/Felts Field have a 20%
chance. The only locations which could be cooler today will be
near the Cascade Crest and this is due to the transition to
onshore flow from the aforementioned BC shortwave trough. The
cooling on the west side of the state will lead to the next issue,
increasing winds in the Cascade gaps late today due to a
strengthening pressure/thermal gradient. By late afternoon, winds
across the Waterville Plateau, Wenatchee Area, and western
Columbia Basin could gust up to 25-30 mph. The full surge of wind
will come overnight and into Monday as a strong cold front trudges
through the region but more on that later.

The other issue for today will be the threat of thunderstorms this
afternoon into the late evening as the atmosphere destabilizes
nicely to the NE of the ejecting CA low. Convection continues to
fire north of the upper low late tonight over Oregon in a region
of steep mid-level lapse rates and moderate amounts of 0-6km shear
(30-40 kts). As the low ejects eastward through the PM and we
heat the lower atmosphere, we should see the nice destabilization
across SE WA into NC ID, with MUCAPE values nearing a rather
impressive 700-1000. The Extreme Forecast Index (EFI) suggests
these values are extreme for mid-April and given the unusual
warmth, that makes some sense. Despite the lofty values of MUCAPE
what is missing is deep 0-6km shear and a strong focus for
prolonged ascent. While the Oregon convection is proliferating in
the deep shear and instability, shear values this far north will
cap out at less than 30 kts. This isn’t favorable for supporting
persistent thunderstorms, but it could still support pulse storms
(I.e short-lived ones) between late afternoon into most of the
evening. Most of the thunderstorms will occur south and east of a
line from the Blue Mountains to Lookout Pass. While these storms
aren’t likely to produce large hail or damaging winds, there is
some concern locally heavy rain is possible as there will be a
band of unusually moist air in this region (precipitable water
values of 150-180% of normal) with cell motions of 10 mph or less.
However the biggest threat of said rains will likely occur just
southeast of our forecast area per the HREF 24 hour rainfall
amounts. HREF probabilities place about a 30% chance of seeing 1”
or more of rain but those chances are largely contained over
Clearwater and Idaho Counties. Over the Camas Prairie the odds are
20% or less. The threat of convection is expected to fall
significantly after midnight due to the passage of the BC
shortwave and a strong cold front which will deliver a much drier
and more stable air mass.

For Sunday night and  Monday the main story will be the passage
of the cold front and a transition to much cooler temperatures
with breezy conditions. 850 mb temperatures will plummet anywhere
from 5-8C which is indicative of a rather strong cold front. These
reading correlate with high temperatures in the mid 50s to mid
60s or a cooling 10-18 degrees. This cooling will be accompanied
by breezy west winds which will gradually fan out from the
Cascades this evening and across the entirety of the Inland NW
overnight. The peak wind gusts tonight will occur over the
Wateville Plateau this evening and spread over the Palouse and
Spokane area after midnight. Peak gusts will generally range from
25-30 mph with slightly stronger winds on the Waterville Plateau.
The breezy conditions will dip a bit in the morning but should
pick up again in the afternoon with widespread 25-35 mph readings.

The winds later this afternoon and again tomorrow afternoon could
lead to patchy blowing dust across the Columbia Basin by newly
plowed fields however the forecast speeds aren’t really conducive
to widespread blowing dust. The other issue is the winds will
combine with relative humidity values between 20-25% across the
Waterville Plateau and Grant County this PM. If there were
widespread pre-greenup fuels there would be some fire concerns,
however the early Spring has likely alleviated much of that
concern. There will be some concern on Monday as well with RH
values dropping below 25% from the Okanogan Valley south to the
western Columbia Basin coinciding with the gusty winds, however
the cooler temperatures should dampen the threat. fx

Tuesday through Saturday: Behind Monday`s cold front, snow levels
will plummet allowing for chances of light snow down to valley
floors Tuesday morning. Little to no lowland accumulations are
anticipated, and even for the mountains the risk of significant
snowfall is low. Model guidance is now giving Stevens Pass has a 40%
chance of seeing at least 3 inches, and Snoqualmie a 60% chance of 3
inches. If the convergence zone sets up over a pass, heavier
snowfall rates may lead to minor travel disruptions, but generally
roads will be warm enough to mitigate impacts.

With afternoon highs in the low to mid 50s, Tuesday will be the
coldest day of the week before ridging returns and temperatures
steadily rebound through the rest of the week. Highs will rise back
to the mid 60s by next weekend. Intermittent showers will continue
through Wednesday before things dry out Thursday through Saturday.
/Fewkes
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&&

.AVIATION...
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06Z TAFS: VFR conditions will persist over the next 24 hours with
thin high clouds. Cascade gap winds will increase in the
afternoon with a cold front approaching. KEAT will see sustained
northwest winds picking up to 15 to 20 knots after 00Z. There is
a 10% chance of elevated thunderstorms from KLWS to Lookout Pass
starting at 21z tomorrow afternoon.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is low confidence thunderstorms will make it as far north as
KLWS/KPUW Sunday afternoon.

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

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
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&&

.PRELIMINARY POINT TEMPS/POPS...
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Spokane        74  44  61  35  52  32 /   0   0   0   0  20  10
Coeur d`Alene  73  43  59  34  50  32 /   0   0   0   0  30  20
Pullman        71  43  55  35  48  32 /   0  10   0   0  20  10
Lewiston       77  49  64  40  56  37 /  10  20   0   0  10  10
Colville       75  41  67  33  53  31 /   0   0   0   0  30  20
Sandpoint      71  43  60  35  47  32 /   0   0   0  10  50  40
Kellogg        72  44  55  35  46  34 /   0  10   0  10  50  30
Moses Lake     79  45  66  37  58  36 /   0   0   0   0   0   0
Wenatchee      76  48  61  38  56  36 /   0   0   0   0   0   0
Omak           77  46  66  36  59  34 /   0   0   0   0   0   0
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&&

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

$$