265
FXUS66 KOTX 281202
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
502 AM PDT Sun Apr 28 2024

.SYNOPSIS...
Sunday and Monday will be windy with gusts around 35 mph. Showers
will focus in the mountains today then expand into the lowlands
overnight and Monday with the passage of a frontal system. This
system will also bring snow to the Cascade mountain passes Sunday
night and Monday morning. Temperatures will trend cooler with
areas of frost returning Tuesday morning. Unsettled conditions
return for the remainder of the week.


&&

.DISCUSSION...
Today through Monday night: Unsettled weather pattern continues over
the Inland Northwest as shortwaves continue to drop into the
region from the Gulf of AK. Surface analysis indicates heights
falls are ongoing over south-central Alberta resulting in a 6 mb
pressure gradient across the forecast area as of 2AM. These
gradients will continue to increase today closer to 9 mb resulting
in stronger winds than those experienced on Saturday. Winds will
generally be out of the south and southwest this afternoon with
speeds across the Okanogan Valley, Waterville Plateau, Columbia
Basin, West Plains, and Palouse close to 20 mph. HREF places the
highest probabilities for these speeds from Omak to Waterville
and from the Tri-Cities to Airway Heights. Accompanying wind
gusts will be on the order of 30 mph. It will also be noticeably
breezier for our northern mountains and Idaho Panhandle with
sustained speeds of 10-15 mph and gusts near 25 mph except some
higher gusts on the higher peaks. Precipitation will once again
focus over the rising terrain of NE WA and N ID as scattered
showers. Not ruling out a few weak thunderstorms though
instability parameters and calibrated thunder chances are lower
than those predicted on Saturday.

A more robust shortwave drops into the Northwest overnight into
Monday ushering a potent cold front through the region with 850mb
temperatures cooling from 4C to 0C. Stronger dynamics will lead
to more widespread showers which will mix or change to snow for
elevations as low as 2500 feet Monday morning. The most impactful
snow will be on the Cascade passes where several inches of snow
will be possible overnight into Monday morning bringing a return
to winter travel conditions. Winter weather advisories were issued
to address these concerns.

Monday will feature another shot of strong winds with a shift toward
a westerly direction. HREF probabilities for sustained winds of
20 mph are 50-90% for a much larger area stretching from the
foothills of the Cascades, across the COlumbia Basin, and into the
lower Idaho Panhandle including the Palouse and L-C Valley.
Sustained winds on the order of 20-25 mph will be accompanied by
gusts of 30-40 mph. Locally stronger winds 30 G 45 mph are
possible on the Waterville Plateau and in the foothills of the
Blue Mountains. Hi-res models are also indicating isolated gusts
35-40 mph with short-lived downdrafts near convective showers
that develop in the Basin Monday around midday to early
afternoon. Thinking these showers are very possible given the
projected lapse rates and midlevel forcing. Patchy blowing dust
will also be possible near freshly tilled fields around Moses
Lake, Othello, and Warden as afternoon humidity values dip near
20% though this comes with low confidence.

Winds will weaken Monday evening and overnight with clearing
skies. Several areas will carry a risk for freezing temperatures.
There is at least a 30-40% chance along and north of a line from
Pullman to Mose Lake for freezing temperatures. Probabilities
increase closer to 50% across the upper Basin and Okanogan Valley
then 60-90% for the northern mountain valleys. /sb

Tuesday through Saturday...Looking ahead to the latter half of the
week, the forecast becomes somewhat uncertain, characterized by a
split in ensembles starting Wednesday night. Before that, a
shortwave will slide through the region bring an unsettled pattern
to the region Tuesday. There is a widespread chance of showers on
and with the instability with afternoon heating, thunderstorms are
not out of the question during the afternoon and evening. Winds will
also be a bit breezy, but will not be as high as what is seen
Monday. As we move into Tuesday night, the threat of showers will
decrease along with temperatures dipping into the low to mid 30s,
leaving a heightened risk of frost across the area. Those with
sensitive plants should take precautionary measures, particularly as
temperatures flirt with freezing. Showers will increase again
Wednesday afternoon, mainly over the ID Panhandle and mountainous
terrain. Winds will continue to decrease Wednesday from what is seen
Tuesday. High temperatures will warm into the mid 50s to low 60s

However, the picture becomes muddled as we move into Wednesday
night, as differing ensemble models paint contrasting scenarios.
While some models indicate a continuation of a troughing pattern
accompanied bu the arrival of a shortwave ridges, others suggest the
intrusion of a ridge into the region. Should the ridge remain
offshore, temperatures are poised to be cooler than initially
anticipated, with the area remaining unsettled within the trough.
Nevertheless, there is a growing consensus that the ridge will make
landfall ushering in warmer temperatures. /KM

&&

.AVIATION...
12Z TAFS: Spotty showers remain in the Idaho Panhandle this
morning and will expand once again into the mountains of
Northeastern WA. Local cigs to 3000 feet will be possible under
heavier showers. Otherwise, winds will increase after 18Z region-
wide with a general south to southwest direction. Gusts around
30-35 mph will be possible in the Okanogan Valley, Columbia Basin,
and near the Blue Mountains. There is a 40-50% chance for morning
stratus to develop between Pullman and Spokane around 15Z with
cigs between 1000-2500 ft AGL. MVFR cigs will lift above 3000 feet
19-20z.

Heads up, a potent cold front Sunday night into Monday will bring
more widespread precipitation to the Idaho Panhandle and Eastern
third of WA. Rain will transition to wet snow for elevations
around 2500 feet and higher which includes Pullman, Spokane, and
Coeur D Alene. Confidence is low for accumulations with steady
winds keeping temperatures above freezing during this time. Winds
will become gusty Monday from the west as well with potential for
brief gusts around 40-45 mph. /sb



FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is moderate to low confidence for scattered to broken MVFR
stratus developing Sunday morning 14-18Z between Pullman and
Spokane. Wind direction is favorable and supported by at least 50%
probabilities on the HREF so retained in the latest TAF package.
Isolated lightning strikes will be possible again in Northeastern
WA and North Idaho. The threat is lower than Saturday but tough to
rule out completely.

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

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        58  39  51  32  53  36 /  20  30  70  10  30  10
Coeur d`Alene  54  38  48  31  50  35 /  40  40  90  20  30  20
Pullman        55  37  48  31  49  33 /  20  30  90  30  60  20
Lewiston       64  44  55  37  56  37 /  20  30  80  20  40  20
Colville       58  34  51  26  55  31 /  40  30  80  10  30  10
Sandpoint      52  38  47  32  48  35 /  80  70  90  40  50  20
Kellogg        51  39  44  33  45  35 /  70  60 100  50  70  30
Moses Lake     63  39  59  34  60  36 /  10  10  30   0  10   0
Wenatchee      60  39  55  37  57  38 /  10  20  20   0  10   0
Omak           63  37  57  32  58  36 /  10  10  30   0  10   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Winter Weather Advisory from 11 PM this evening to 11 AM PDT
     Monday for Western Chelan County.

&&

$$