786
FXUS66 KOTX 042217
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
317 PM PDT Sat May 4 2024

.SYNOPSIS...
A slow moving low pressure system will bring widespread rain to
the Inland Northwest Sunday and Sunday night. As the low pulls
out of the region on Monday and Tuesday, the weather will become
cool, showery, and breezy. Warmer and drier weather will arrive
late next week. Next weekend has the potential to deliver our
warmest temperatures of the spring so far.

&&

.DISCUSSION...

Tonight and Sunday: As of 2PM, an elongated upper low making
landfall along the coast of Oregon and northern California was
spreading rain inland from southwest BC to as far south as central
California. Water vapor satellite imagery shows two distinct
circulations with one off the coast of central OR dropping south
and the other pivoting inland over northern California. As these
circulations move inland overnight, the morning model runs
generate an band of wrap around precipitation that will spread
northward overnight into our region. Around sunrise, ensemble
consensus has the rain band extending from about Bend Oregon to
Tri Cities to Spokane. By afternoon, significant precipitation is
forecast to pivot west toward Moses Lake, Wilbur, and Republic
before migrating eastward Sunday night. If the band evolves this
way, the majority of central/eastern Washington and north Idaho
will receive much needed rainfall. The National Blend of Models
(NBM) gives north Idaho and the eastern third of Washington a 60
to 80 percent chance of a quarter inch by Monday morning. And the
NBM generates a 50 to 60 percent chance of a half inch or more
from Ritzville to Tri Cities by the evening. Precipitation
deficits were common region-wide during the month of April, so
rain of this magnitude will be important for our dryland farmers
in the Columbia Basin, Palouse, and West Plains. Unfortunately, a
chilly rain will not be pleasant for outdoor activities on Sunday.
For Spokane, our latest guidance generates between a tenth and a
quarter inch of rain across the metro in the morning with
temperatures in the mid to upper 40s.

Monday and Tuesday: By Monday, our low will be emerging east of
the Rockies. Surface pressure falls over Montana will contribute
to a tight westerly pressure gradient across the Inland Northwest.
West or southwest winds of 20 to 25 mph with gusts to 35 mph will
be common from the Waterville Plateau across the Columbia Basin to
the Palouse and West Plains. Mid-level instability will be
reinforced by an incoming Pacific shortwave. With 500mb
temperatures as cold as -27C in the afternoon, rain and mountain
snow showers will develop with the most concentrated shower
activity over the mountainous terrain of north Idaho, northeast
Washington and along the Cascade crest. But even widely scattered
showers in central Washington before surface dewpoints in the 30s
are replaced by dewpoints in the 20s Monday night and Tuesday. A
few lightning strikes will be possible over the mountainous
terrain around Republic, Colville and Northport in the afternoon
as the NAM and GFS generate up to 100 to 300 J/Kg of surface based
CAPE.

Cooler and drier air will spill east of the Cascades Monday night
into Tuesday. Snow levels will fall as low as 2500 to 3000 ft
Tuesday and Tuesday night. Precipitation amounts by Tuesday and
Tuesday night will be light and mainly orographic. What little
snow falls will be in the mountains of north Idaho and along the
Cascade crest. Tuesday afternoon has the potential to be a graupel
or small hail day in north Idaho with highs in the low to mid 50s,
steep lapse rates, and low freezing levels. And it will be windy
Tuesday with more west winds between 15 and 20 mph with gusts of
30 mph or more across similar areas as Monday. The deep low over
Montana won`t move much until Wednesday.

Wednesday through Saturday: To quote the Beatles` song, "Here
Comes the Sun". The medium range models are in good agreement that
the Pacific Northwest will experience a warming and drying trend
over the second half of the week. The formation of a Rex Block
over the western U.S. will likely deliver our warmest temperatures
of the season by Friday into the weekend. The National Blend
advertises widespread 70s by Friday and our first 80s of the
season for central WA and the L-C Valley. /GKoch

&&

.AVIATION...
18Z TAFS: Mid to high level clouds will continue to increase
across the Inland NW and gradually lower this afternoon and
evening as bands of precipitation move up from the south. Light
rain is expected across the Cascades by the morning hours on
Saturday with rain at KEAT by 16Z with local MVFR ceilings. South
and easterly winds will pick up with the front approaching.
Ceilings will continue to lower overnight.  Rain
bands will increase across KLWS, KPUW, KCOE to KGEG after 05Z.
There is a 90% probability of MVFR ceilings for KGEG-KCOE-KPUW
after 10Z.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for
VFR conditions through Saturday night. Chances for MVFR ceilings
expand early Sunday morning to KLWS, KPUW, and KGEG. There is low
probability of visibility dropping below 3SM at Taf sites.
Ensembles have brief periods of 2SM at KPUW. JDC

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

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        43  50  40  57  36  59 /  50 100  80  40  10  10
Coeur d`Alene  43  50  39  53  36  55 /  40 100  90  70  20  20
Pullman        40  47  38  52  34  53 /  80  70  90  60  30  20
Lewiston       48  56  45  60  41  59 /  80  70  90  60  30  20
Colville       43  52  39  60  34  61 /  20  90  90  60  30  20
Sandpoint      44  50  40  52  36  54 /  30 100  90  80  40  40
Kellogg        46  47  40  48  37  49 /  50  90 100  90  50  50
Moses Lake     47  58  41  64  38  64 /  60  90  30  10   0   0
Wenatchee      50  59  44  61  41  59 /  40  60  20  20   0   0
Omak           49  62  41  65  38  66 /  20  60  30  20  10   0

&&

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

$$