Area Forecast Discussion
Issued by NWS Spokane, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
000
FXUS66 KOTX 270959
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
259 AM PDT Wed Mar 27 2024

.SYNOPSIS...
A wet storm system arrives today with widespread precipitation in
the form of mainly valley rain and mountain snow. Precipitation
becomes showery Thursday with the potential for afternoon
thunderstorms. Showers will continue into Friday. Then a warming
and drying trend is expected through the weekend into early next
week.

&&

.DISCUSSION...
Today and tonight: A consolidated frontal system will impact the
region bringing a good dose of valley rain and snow to the
mountains. A warm front will push in during the morning hours on
Wednesday followed by the cold front passage late Wednesday
afternoon into Wednesday evening. Snow levels will start out between
2000 to 2500 feet this morning over the Cascades into the Okanogan
Highlands and Waterville Plateau. Slushy accumulations for these
valleys will be possible. Snow levels continue to rise through the
day today reaching between 4000 near the Cascades to 4500-5000 feet
in the Idaho Panhandle by mid afternoon prior to the arrival of the
cold front. This will be low enough for snow over Stevens Pass, Loup
Loup Loup Pass, and Sherman Pass with between 3 to 6 inches
expected. Expect winter travel conditions over these mountain
passes. We may need to issue an a winter weather advisory for snow,
but total accumulations are just below criteria at this time.

Below is the probability for at least 4" of snow for a 24 hour
period ending 5 AM Thursday for these mountain passes based on the
National Bend of Models (NBM) guidance:

*Stevens Pass = 55%, Loup Loup Pass = 5%, Blewett Pass = < 5%,
Sherman Pass = 16%

And there is a 16% chance for at least 6" of snow to fall at Stevens
Pass.

Valleys will see mostly rain and many areas over the eastern half of
the forecast area will receive at least a quarter of inch of rain.
Probabilities of at least a quarter of inch of precipitaiton from
the National Blend of Models (NBM) are as follows:

*Spokane = 50%
*Coeur d`Alene = 60%
*Colville = 70%
*Sandpoint = 75%
*Pullman/Moscow = 60=65%
*Lewiston = 30%
*Omak = 25%
*Wenatchee = < 5%
*Moses Lake = < 5%

And for areas with at least a 5% chance for receiving at least a
half of an inch precipitation:

*Spokane = 5%
*Coeur d`Alene = 10%
*Colville = 15%
*Sandpoint = 20-25%
*Pullman/Moscow = 10-15%
*Lewiston = 5%
*Omak = 5%

There isn`t much cold air advection that comes with the cold front
passage Thursday night. Winds will remain southerly ahead of the
front through Wednesday afternoon. Poor mixing with the stratiform
precipitation will tamp down wind speeds a bit.

Thursday and Thursday night: The Inland Northwest will be in a
conditionally unstable post frontal air mass. Skinny CAPE profiles of
200-300 J/kg support the potential for isolated thunderstorms with
the mountains being most favored at a 20-25% chance of occurring.
The 25% chance for thunderstorms favors the Northeast Mountains and
Idaho Panhandle with a 20% chance more so over the Cascades to the
Okanogan Highlands. The Upper Columbia Basin, Palouse, and Spokane
Area will see a 15-20% chance for thunderstorms. Timing of
thunderstorms will be afternoon into the evening. Main threats will
be for brief heavy downpours, small hail and gusty out flow winds up
to around 30 mph. Models don`t show much in the way of support of
dynamics aloft. This would limit afternoon and showers and
thunderstorm coverage a bit with differential heating being the
dominant contributer to forcing convection. Winds will be breezy in
general on Thursday with breeziest wind gusts of up to 20-25 mph
over the basin and up the the Okanogan Valley. /SVH

Friday through Wednesday: The low digs south off the west coast
with a ridge building into the Gulf of Alaska. The Inland
Northwest is still in this general trough like pattern. With
afternoon 500 mb temps of -31C across the area and instability
shown in the GFS and NAM, have kept the idea of a small chance
(20%) of afternoon thunderstorms. The area of concern looks to be
the north Idaho Panhandle, but cannot rule out some graupel
showers for much of the region. Drier air quickly begins to move
into the region Friday night and Saturday. Clearing skies and
drier air Saturday morning means some cooler temps to wake up to,
especially across northern WA where lows in the mid to upper 20s
is forecast. There is enough low level moisture for some afternoon
showers across the Idaho Panhandle, otherwise expect mostly clear
skies Saturday through Monday. Temperatures will warm a bit each
day and peak on Tuesday as the ridge folds over the region and our
850 mb temps warm as winds become more southerly. Tuesday will see
temps in the 60s and around 70 in the deep Columbia Basin, which
is about 10 degrees above average for the beginning of April.

Discrepancies enter the forecast as we move toward midweek and
beyond. They agree on the ridge breaking down, but differ on a
potential trough and its influence/placement across the Northwest.
Confidence is moderate to high of temperatures cooling down to
average and showers returning, especially across the mountains mid
to late week. /Nisbet

&&

.AVIATION...
06Z TAFS: High pressure briefly builds in overnight, with some
risk for fog developing around GEG-SFF-COE. But confidence only
leans toward vicinity or perhaps shallow fog at this time. Rain
increases from west to east through the day bringing lowering
cigs and possible reduced visibility in the steadier rain. MVFR
conditions are projected with the heavier periods of rain. Expect
mountain obscurations.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Low confidence in
fog overnight at TAF sites. High confidence in rain spreading
over the region Wednesday, high confidence in precise timing.
Some snow may mix in early near EAT, but confidence is very low.

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

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        48  36  51  34  52  31 / 100  90  60  50  50  10
Coeur d`Alene  46  36  49  33  49  30 / 100 100  60  50  70  10
Pullman        47  35  50  34  50  31 / 100 100  60  60  60  10
Lewiston       55  40  56  38  55  36 /  80 100  50  50  40  10
Colville       46  34  51  31  52  27 / 100  80  60  60  60  10
Sandpoint      45  36  47  34  48  30 / 100 100  70  70  80  20
Kellogg        46  36  46  34  47  32 /  90 100  70  60  80  10
Moses Lake     52  35  57  35  58  34 / 100  20  10  10  10   0
Wenatchee      46  35  54  36  55  36 / 100  20  20  10  10   0
Omak           47  36  55  37  57  32 / 100  50  30  20  40  10

&&

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

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.