Lewiston, Idaho 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

710
FXUS66 KOTX 220550
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
950 PM PST Sat Dec 21 2024

.SYNOPSIS...
Unsettled weather will return this weekend and continue into next
week. Mild temperatures will result in precipitation falling
primarily as valley rain and mountain snow. Check mountain pass
forecasts and conditions often before traveling. Periods of heavy
mountain snow will be possible late next week.

&&

.UPDATE...
A moist boundary layer and light winds across central Washington
has allowed for dense fog to form across the Columbia Basin this
evening. Persistent visibilities of a half mile or less are being
observed at the Moses Lake and Ephrata airports. Webcams are also
showing low visibilities in these areas and along I-90 and we
have received several reports of very low visibility. Therefore,
we have issued a Dense Fog Advisory for the Waterville Plateau and
the Columbia Basin through 10 AM Sunday. Expect fog to creep into
the Spokane area with low visibility west of downtown on the West
Plains. If you encounter dense fog, slow down, use your low- beam
headlights, and leave plenty of distance ahead of you. /vmt

&&

.AVIATION...
06Z TAFS: Widespread MVFR conditions and localized IFR conditions
are expected into Sunday morning due to a saturated boundary
layer. The one exception is Pullman where the HREF guidance is
favoring a better chance for VFR conditions. The next weather
system crosses the Cascades into KEAT Sunday afternoon and will
spread eastward through the late afternoon and evening.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is high confidence for widespread IFR/MVFR conditions for
most of the region through at least 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

&&

.PREV DISCUSSION... /issued 331 PM PST Sat Dec 21 2024/

DISCUSSION... Tonight through Monday: A large low near the
Aleutian Islands will send additional weather systems in from the
southwest resulting in a mild and wet pattern. The first wave
moving in today will bring continued widespread precipitation with
the main focus this evening shifting from Eastern Washington into
the ID Panhandle while Central WA begins to dry out.
Precipitation will fall mainly as valley rain and mountain snow as
snow levels fall to 3500-4000 feet. This will result in light
accumulations for many of the passes in the Cascades, Sherman
Pass, and Lookout Pass. Models show the brunt of the precipitation
over Lookout Pass falling prior to snow levels falling with
accumulations less than 1 inch. For the northern valleys, a few
pockets of near freezing temperatures remain where localized
freezing rain is possible. A Winter Weather Advisory remains in
place for the Okanogan Valley through 6 PM for a wintry mix. A
short wave ridge moves in overnight into Sunday morning which will
promote an abundance of stratus and areas of fog and freezing
fog. The next system spreads more valley rain and mountain snow
across the region starting in the Cascades Sunday afternoon before
spreading into Eastern WA/N Idaho Sunday Night. Snow amounts in
the mountains will generally be 1 to 3 inches, except closer to
4-5 inches for Stevens Pass. One exception to the valley rain is
the Methow Valley, and East Slope Valleys. NAM soundings as well
as HREF suggest a mainly snow event for the Methow Valley with 1-3
inches, with precipitation possibly starting as snow around Lake
Wenatchee with 1-2", and a rain/snow mix for Leavenworth area. JW

Monday night through Saturday: Much of next week looks to be quite
unsettled with the greatest potential for snow being Wednesday
night through Thursday. Christmas eve (Monday) will feature some
chances for snow as a compact low pressure system approaches the
SW BC coast. Snow levels will be around 2000 feet in the east
slopes of the Cascades and northern mountains overnight.
Precipitation type will be rain mostly everywhere else. Low level
upslope flow and weak isentropic ascent in the 290-295K layer
support a light burst of snow overnight Monday in the east slopes
of the Cascades. The greatest chances for 1+ of snow is from
Leavenworth to Stevens Pass on US-2 (40-90% chance), Twisp to
Mazama on Highway 20 (90% chance), and Wauconda Pass to Sherman
Pass on Highway 20 (70% chance).

Christmas day appears to feature a short break for some in between
systems with a shortwave ridge quickly traversing through the
region. The east slopes of the Cascades has the best chance of
seeing snowfall on Christmas night as the next system moves in.
This next system looks more robust for snowfall per ensemble
guidance. Isentropic ascent looks stronger than the Tuesday
system. From 4pm Wed - 4 pm Thursday, Stevens Pass has a 50%
chance of 12+ of snow. The snowfall has been trending up on the
CMC/EC ensembles but the GEFS is holding steady below 12 as the
moisture plume goes south of us. Details will be ironed out as the
event comes closer. Lowland locations also carry large ensemble
spread, but the 10th percentile accumulations are 2+ for
Leavenworth, Winthrop, and Republic.

The parent trough still lingers over the northern Pacific into the
late week and next weekend, keeping the active wintry-ish pattern
alive and well. DB


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        33  40  36  40  35  41 /   0  10 100  10  40  70
Coeur d`Alene  33  40  34  41  34  40 /  10  10 100  30  30  70
Pullman        32  44  38  45  37  41 /   0  10 100  20  40  70
Lewiston       36  48  40  50  39  46 /   0  10  90  20  30  60
Colville       29  36  33  38  32  36 /  10  30 100  10  40  80
Sandpoint      33  37  33  39  33  36 /  20  10 100  70  30  80
Kellogg        35  40  34  39  33  39 /  20  10 100  80  30  80
Moses Lake     32  40  35  42  36  45 /   0  40  80   0  70  60
Wenatchee      32  36  32  39  34  40 /   0  70  80   0  80  50
Omak           30  35  32  38  34  37 /   0  40  90   0  70  60

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Dense Fog Advisory until 10 AM PST Sunday for Moses Lake Area-
     Upper Columbia Basin-Waterville Plateau.

&&

$$