859
FXUS66 KOTX 092239
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
239 PM PST Sat Nov 9 2024

.SYNOPSIS...
A weak weather system arrives over the weekend bringing a chance
of light rain and high mountain snow. Unsettled weather will
continue through next week with periods of mountain snow and
lowland rain. Snow over mountain passes may be moderate to heavy
at times with winter travel possible.

&&

.DISCUSSION...
...Light snow to impact Cascade Passes this week, starting Sunday
at Washington Pass and Monday at Stevens Pass. Heavy mountain
snow arrives Tuesday evening into Wednesday...

Tonight through Monday night: There will be two storm systems
coming through the region through Monday night. The first system
will be weak and mainly rain for the lowlands and mountain
passes. The second system will have a lot more structure and
moisture with periods of moderate precipitation intensity. A
wintry mix of snow and rain will be possible in the far northern
valleys with the second system, otherwise this will once again
rain to the lowlands and snow to the mountains. Those planning to
travel across the mountain passes are urged to keep an eye on the
forecast and be prepared for winter travel conditions.

Storm system 1: Saturday evening through Sunday morning. This is
largely a decaying frontal band limping through the region
bringing light rain and mountain snow. QPF amounts will range from
a few hundredths in the lee of the Cascades to around 0.15" in
portions of North Idaho and Eastern WA. Snow levels will be around
5000-6000 feet with only light snow accumulations expected on the
highest passes. Overall impacts will be low.

Storm system 2: Sunday evening through Monday evening. This system
will be more typical of our winter storm systems with a 6-8 hour
period of warm sector precipitation for most areas outside far SE
WA and the lower Idaho Panhandle under south/southeast flow. This
will erase the Cascade rain shadow but bring some downsloping in
the foothills of the Blue Mountains and Lewiston Area. That will
change Monday morning as an occluded front presses inland and
ushers a north to south band of precipitation through the region
with drying in the lee of the Cascades and slowly progressing east
through the afternoon. Precipitable waters are near 200% of
normal with this system and given the stronger dynamics, QPF
amounts will range from 0.25-0.75" with some of the northern
mountains receiving over an inch. The aforementioned drier areas
around Pomeroy, Lewiston, and Winchester only look to pickup
around a tenth or less. As for precipitation type, the cloud
shield arrives Sunday afternoon-evening trapping the warmest
temperatures of the day. This does not bode well for lowland snow
despite the classic cold air damming setup. This leads to moderate
to high probabilities for rain vs snow in the lowlands.
Precipitation intensity may drive wet snow as low as 3000 feet at
times around Winthrop, Republic, and Colville with no
accumulation. WA Pass has a 30% chance for a foot of snow from
this event. Stevens Pass looks to start off as rain with a
transition to snow Monday morning as the front passes through.
Snow advisories have been issued for Washington Pass with a long
duration period of light snow starting Sunday evening and
continuing into Tuesday. We will be revisiting winter advisories
for Stevens Pass for Monday evening into Tuesday.

Winds will become breezy to gusty Monday afternoon shifting from
the south to southwest with cold front passage. There is a 30-50%
chance for gusts in excess of 30 mph across the open Columbia
Basin with only a 5% chance for speeds to reach 40 mph.

Temperatures Sunday will be seasonably cool with lows in the 30s
and highs in the 40s. Monday will start off warmer with heavy
cloud cover and precipitation falling then warm into the 40s and
50s in the afternoon with good mixing and end of the preciptiation
by the afternoon. There is not high confidence for freezing
temperatures but any breaks in the clouds at night could allow for
radiational cooling and pockets of near freezing temperatures.
Where this occurs, odds will be increased for areas of fog and
potential for black ice. /sb

Tuesday through Saturday:
Our active pattern will continue for the mid-to-latter stages of
the week as a series of weather systems impact the region. For
Tuesday night into through Thursday, snow levels look to remain
above 3500`, though they are likely to drop for Friday and
Saturday. Expect valley rain and mountain snow with each system,
with the mountains and mountain passes the main concern for
accumulating snowfall. Widespread and largely beneficial rain will
occur across the lower elevations. In addition to the precip,
breezy southwesterly winds are likely each day from Tuesday
through Thursday, especially across the Columbia Basin and
Palouse. /KD

&&

.AVIATION...
18Z TAFS: Areas of dense fog impacting the valleys of NE WA and
North Idaho including COE, SFF, and GEG will begin to lift 18-20Z
with potential for MVFR stratus through 22z. Otherwise, Midlevel
clouds are moving in ahead of an approaching frontal band poised
to bring light rain and MVFR or lower restrictions after 07z. This
will be a top down lowering of cigs with -RA creating visibility
2-5SM. Following the rain, stratus is likely to remain across NE
WA and N ID with periods of drizzle. Widespread mtn obscrns are
expected. There are lower probabilities for restrictions in
Central WA at EAT/MWH however, some radiation fog development
cannot be ruled out 13-16z following light rain. This comes with
low confidence.


FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Moderate to high confidence for current dense fog to lift this
morning with low to moderate confidence how quickly the stratus
will break to return to VFR skies for NE WA and N ID. There is
moderate confidence for low stratus to return with and following
the rain Sunday morning.

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

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  45  42  50  37  48 /  80  50  70  90  70  60
Coeur d`Alene  38  45  41  48  37  45 /  80  60  70 100  90  80
Pullman        39  47  42  50  37  46 /  80  60  50 100  90  70
Lewiston       42  53  44  56  41  53 /  60  50  30  90  80  60
Colville       36  47  40  47  36  45 /  80  40  90 100  80  60
Sandpoint      38  44  40  46  38  42 /  90  50  90 100  90  90
Kellogg        36  49  38  48  36  39 /  80  70  70 100 100  90
Moses Lake     36  50  44  54  40  53 /  60  10  80  80  20  20
Wenatchee      35  47  40  52  38  50 /  50  20 100  90  20  20
Omak           34  46  41  53  35  50 /  40  20 100  90  30  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Winter Weather Advisory from 6 PM Sunday to 1 PM PST Tuesday for
     Western Okanogan County.

&&

$$