Area Forecast Discussion Issued by NWS Spokane, WA
000
FXUS66 KOTX 121826
AFDOTX
Area Forecast Discussion
National Weather Service Spokane WA
1126 AM PDT Tue Mar 12 2024
.SYNOPSIS...
Another round of rain and snow lingers on through Tuesday evening
bringing additional mountain snow to the region and lowland rain.
High pressure will build over the Pacific Northwest Thursday into
next weekend bringing warmer temperatures and dry weather.
&&
.DISCUSSION...
Morning Update: Our winter weather advisories for Sherman Pass
(WA) and Lookout Pass (ID) have ended as snowfall has come to an
end and road conditions are improving. After a break in the
precipitation and clouds early this morning, we are seeing the
instability building with showers and storms that will develop
across the eastern Basin, the Palouse, into the West Plains and
far eastern Washington in just a few hours. Per the 12z KOTX
sounding, our temperatures are 500mb have cooled compared to the
last 24 hours which will further enhance the lapse rates and erode
away the stable layer allowing a bit more CAPE to be present.
Lower topped storms with a layer of moisture in the -10C to -20C
layer seems conducive for small hail and lightning. The going
potential for storms today being 20-25% seems reasonable, given
the environmental conditions and comparing the previous conditions
just two days ago when we saw some small hail and lightning.
Late this evening we are still expecting to see a Convergence Zone
setup into the Cascades producing a few hours of 1"/hour snowfall
rates. Confidence is moderate that this will all impact Stevens
Pass, since it has the potential to wavier and shift north or
south. /Dewey
.Previous Discussion...
Today through Wednesday: A Gulf of Alaska Low is pushing a cold
front through the Pacific Northwest today and early Wednesday.
Ensembles are in decent agreement with the timing of the front.
With 850mb temperatures hovering near the 0°C, it is pointing to a
mountain snow, valley rain event. The west to east trajectory of
the front puts highest snow amounts in the Cascades with near a
foot expected for Stevens Pass. The area has a 50% probability of
at least 8”. The mountains across Northern Washington and the ID
Panhandle should receive 3-6” through tonight. Precip amounts
across the region are in the 0.1-0.2” range. Models are showing
enough instability to possibly generate an isolated thunderstorm
and/or graupel over extreme Eastern WA and ID Panhandle this
afternoon. Tuesday highs will mid 40s to upper 50s. Winds will be
breezy with the frontal passage. Gusts near 30 to 40 MPH are
possible across the Basin. Overnight lows will dip into the 20s
and low 30s Tuesday night. A ridge will start to build along the
coast behind the front. It will lead to warm drying trend starting
early Wednesday morning. Lingering mountain snow showers will
slowly taper off by Wednesday afternoon. /JDC
Wednesday Night through Tuesday: Models in fantastic agreement of
a strong ridge building across the Pacific Northwest. Skies will
be clear to partly cloudy through the remainder of the week and
weekend with light winds. Temperatures will begin near average
readings Thursday, which is lows in the upper 20s and mid 30s and
highs in the upper 40s to mid 50s, and warm each day peaking
Sunday and/or Monday. By the weekend we will be looking at temps
in the upper 50s to mid 60s with lows above freezing for the
valley locations. This is 8 to 13 degrees above average.
Uncertainty enters the forecast come Tuesday with a potential
breakdown of the ridge as a trough moves down from Alaska.
Currently the ensemble clusters are showing a 60/40 split with 60%
of the models showing the ridge weakening and heights lowering
and 40% keeping the ridge going strong. There is a 20-30% chance
of showers in the afternoon across northeast WA and ID Panhandle,
but if the ridge remains it will be near zero. /Nisbet
&&
.AVIATION...
18Z TAFS: Gusty southwest winds will accompany the frontal passage
during the late morning and afternoon hours today, gusts 20-30
mph. Surface based convective storms are forecast this afternoon
from about 12 pm through 8 pm for eastern WA and the ID Panhandle.
Airfields most likely to be impacted by brief heavy downpours,
gusty winds, and brief MVFR/IFR conditions due to storms include
GEG, SFF, DEW, COE, CQV, SZT, and PUW. Thunderstorm potential
across the region is around 20-30%. Wednesday morning lingering
moisture could generate fog/stratus resulting in brief IFR
conditions for the northern valleys and DEW.
FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Moderate to high confidence in MVFR conditions with precipitation
onset in more stratiform rainfall through Tuesday afternoon and
evening gusty southwest winds. Low confidence on thunderstorms
impacting airfields, therefore no mention in the TAFs. Low
confidence for fog bringing IFR conditions into the Spokane area.
/Dewey
------------------------
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 49 29 47 28 51 29 / 80 30 0 0 0 0
Coeur d`Alene 46 28 43 25 48 28 / 90 50 10 0 0 0
Pullman 47 29 43 28 49 29 / 80 50 10 0 0 0
Lewiston 54 34 50 32 54 34 / 70 20 0 0 0 0
Colville 46 26 48 25 50 27 / 70 50 0 0 0 0
Sandpoint 42 29 41 27 46 28 / 90 70 20 0 0 0
Kellogg 43 30 40 26 46 29 / 100 80 30 0 0 0
Moses Lake 54 29 53 29 56 32 / 30 10 0 0 0 0
Wenatchee 49 32 51 33 55 36 / 30 0 0 0 0 0
Omak 52 30 53 32 56 35 / 30 10 0 0 0 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Winter Weather Advisory until 11 PM PDT this evening for Western
Chelan County.
&&
$$