236
FXUS66 KOTX 230616
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1016 PM PST Fri Nov 22 2024

.SYNOPSIS...
The weekend into early next week will feature seasonably cool
temperatures and chances for valley rain and brief snow and
periods of mountain snow. Moderate rain amounts for portions of
eastern Washington and the Idaho Panhandle will lead to the threat
of rock and mud slides near steep terrain.

&&

.DISCUSSION...
Far north Idaho around Bonners Ferry has been on the rain/snow
line the last 24 hours. Early evening spotter reports north of
Bonners Ferry observed a couple inches of wet accumulation through
the day with a temperature near 32 degrees. The airport has
reported a change over to rain this evening with a consistent 32
degrees suggesting that the air aloft has warmed a bit, snow is
probably not far away since low level winds on the NAM and GFS
remain out of the east through the night. The forecast has been
updated to place the snow level between 2000-2500 feet in that
area until morning with up to 2 inches in the valley and 4 to 6
inches above 3000 feet.

Another problem area through Saturday morning will be the Gwen
burn scar south of Julietta, ID. An early morning report of
boulders on Highway 12 in the burn scar indicate how susceptible
this area is to soaking rain. A Flood Advisory highlighting the
potential for rock/mud slides is in effect through the morning
with an additional half inch to inch of rain expected. /GKoch

.PREVIOUS DISCUSSION...
Tonight through Sunday Night: Strong low pressure system will
continue to spin off the Washington and southern BC coast. The
first band of rain that brought moderate amounts of rain to the
region this morning is exiting to the north. The next area of rain is
already moving across central WA and will keep rain going across
the eastern third of WA and the ID Panhandle this evening through
Saturday morning. Most of the aforementioned locations will see
another quarter to half an inch of rain...with parts of the ID
Panhandle seeing up to three quarters of an inch. Probabilities of
three quarters of an inch of rain through Saturday afternoon are
over 90% for Sandpoint and Kellogg, and 60-75% for Bonners Ferry,
St Maries, Pullman and Deer Park. The Spokane area has about a
30-45% chance.

Snow levels this evening will be generally be 4k ft or higher.
Towards Saturday morning they will lower down to 3-4k ft. There is
some stubborn cold air in the Methow and Bonners Ferry northward.
They will transition to rain in the next hour or two, if they
have not done so already. Fortunately the Methow valley will not
see much more precip this evening or Saturday. Bonners Ferry will
need to be watched, as their temps will dip just below freezing
Saturday morning and they could see light accumulations as the
precipitation begins to wind down.

Saturday precipitation will be mostly confined to the WA/ID border
eastward. By Sunday morning, a shortwave ridge builds into the
area with a weather disturbance moving through. Upslope flow into
the Cascades will bring a 40-60% chance of snow. Snow chances
across northern WA and the ID Panhandle are about 30-50%. Valley
temps will be warm enough by mid to late morning that snow is not
expected to accumulate in the valleys. /Nisbet

Monday and Tuesday: An upper-level low will remain planted offshore
through Monday, slinging weak disturbances into the Inland Northwest
and keeping chances for light precip in the forecast. Snow levels
fluctuating between 1.5k and 3k ft will bring intermittent snow for
the mountains and mountain passes and a mix of rain and snow for
valley locations. Valleys north of US-2 have the best chance of
receiving lowland snow Monday, though confidence in amounts is low
due to the potential for abundant boundary layer moisture and fog
formation to keep lower elevations on the warmer side. Chances for
at least 1 inch of lowland snow on Monday range from 10 to 30
percent north of a line from Waterville to St. Maries. Heading into
Tuesday, the offshore upper-level low will track to the southeast
and move inland over the Oregon/California border. Precip chances on
Tuesday for our area will recede to the Cascades, Idaho panhandle,
and eastern third of Washington.

Wednesday through Friday: We`ll transition into a cool northwesterly
flow regime as a ridge of high pressure amplifies off of the coast
over the second half of next week. Temperatures will gradually
decrease with highs in the 30s and lows in the teens to 20s. The
greatest uncertainty for this period is in regard to precip chances.
Models have yet to come to a consensus on where exactly the ridge
axis will set up offshore. If the axis is close enough to the
coastline, any shortwave disturbances that drop down the east side
of the ridge will be deflected into Montana and will bring little to
no precip to eastern Washington and Idaho. If the ridge is further
west of the coastline, shortwave disturbances may drop right into
Washington and Idaho resulting in more precipitation. Currently the
forecast has a 20 to 50 percent chance for precip for the Cascades,
Idaho panhandle, and the eastern third of Washington, though these
chances are subject to change over the next few days as model
solutions converge. /Fewkes


&&

.AVIATION...
06Z TAFS: A persistent band of light to moderate rain won`t move
much until 18-21z when the models finally push it out of eastern
Washington and the Coeur d`Alene area. Soaking rain has been
common region-wide over the last 24 hours. The combination of wet
ground, decreasing winds in the boundary layer, the continued
influx of rain, should lead to decreasing visibility and lower
ceilings region-wide through mid morning. Drier and cooler air
aloft and a modest increase in post-frontal winds should lead to
improvements between 18-00z Saturday as the Inland Northwest
finally dries out. /GKoch

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Moisture laden environments like this are tough as they produce
variable low cloud and visibility conditions. Amendments will be
necessary as rain intensity varies. /GKoch

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

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        38  42  32  44  29  40 / 100  80  10  20  10  30
Coeur d`Alene  37  41  32  42  28  40 / 100 100  20  30  20  50
Pullman        38  41  30  42  30  40 / 100 100  20  10  20  30
Lewiston       42  47  35  47  33  47 / 100 100  10   0  10  20
Colville       34  42  27  39  24  38 /  50  50  10  30  30  40
Sandpoint      35  38  28  37  26  36 / 100  90  30  50  20  60
Kellogg        36  38  31  39  25  41 / 100 100  70  40  20  60
Moses Lake     39  45  32  44  32  42 /  30  20  10  20  20  20
Wenatchee      34  43  31  39  33  41 /  10  10  10  20  40  30
Omak           34  42  29  41  32  40 /  20  10  10  20  30  20

&&

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

$$