136 
FXUS66 KOTX 062348
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
348 PM PST Sun Nov 6 2022

.SYNOPSIS....

Snow will spread eastward into Idaho tonight into Monday morning 
impacting the morning commute. Brisk north winds with cold wind 
chills on Tuesday. Cold temperatures with lows down into the 
single digits and teens will continue through the work week before
slowly moderating next weekend.

&&

.DISCUSSION...
Tonight through Monday: Snow is well underway across north-central 
Washington where current snowfall reports are ranging from 7 inches 
to over a foot of snow across the Methow and Okanogan Valleys. A 
deep upper level low pressure slowly sliding down the BC coast is 
providing deep southwesterly to southerly flow aloft. An area of 
strong isentropic lift is supporting the heavy snowfall that is 
observed in these areas. As expected, this has proven to be a very 
tricky forecast as temperatures above freezing given the deep 
southerly flow aloft for the Wenatchee area through the Spokane area 
and south and up into the Idaho Panhandle. Areas that have been 
under the heavy snow all morning have seen little warm up and are 
sitting at freezing to a couple degrees below freezing. 

As the deep low slowly progresses southward along the northwest 
coast, an impulse rotating around the low will move across the 
Inland Northwest tonight into tomorrow morning. This will bring more 
precipitation across north-central and precipitation across eastern 
Washington and the Idaho Panhandle overnight tonight into tomorrow 
morning. Precipitation looks to begin as rain later this evening for 
the Columbia Basin, the Spokane area and south but will make a 
transition to snow as an Arctic front begins to push southward 
across the region. The greatest uncertainty exists for the exact 
timing of the transition from rain to snow, which would impact the
exact snow totals, especially for the I-90 corridor and south. An
additional Winter Storm Warning has been issued for Boundary and 
Bonner counties where snow amounts between 3 to 7 inches are 
forecasted for Bonners Ferry to Spirit Lake. The NBMv4.1 is giving
Sandpoint a 70% chance to see snow totals over 6 inches through 
tomorrow afternoon. The heaviest snowfall looks to occur between 
the 4am and 10am timeframe, which will lead to impacts for the 
Monday morning commute.

A Winter Weather Advisory has been issued for the far northern 
Columbia Basin (Wilbur, Creston) into the Spokane and Coeur d'Alene 
areas and Shoshone county for tonight through Monday afternoon. 
Since precipitation looks to begin as rain this evening, the 
biggest concern for these areas will be for roads to become icy 
as temperatures cool to below freezing, creating a messy Monday 
morning commute. Snow totals will be around 2 to 5 inches for 
these areas. The NBM gives the Spokane area about a 70% chance to 
see over 2 inches of snow and a 20-40% chance to see over 4 inches
of snow. As road temperatures warm above freezing during the day,
melting snow and much colder air arriving Monday evening will 
make for another slippery evening commute especially across 
untreated roads that were unable to dry during the day. /vmt

Tuesday through Saturday: The deepening upper level low will slide 
south along the west coast Tuesday into Wednesday leaving the Inland 
Northwest under cold advection from the north and weak warm 
advection from the south. Mid-high level moisture should exit to the 
east with the energy from the Monday storm system. However, cloud 
cover will play a part into our daytime and overnight temperature 
achievements. The take away message if you stop reading here is 
temperatures will be bitterly cold through the week ahead with 
daytime and overnight temperatures around 20 degrees below normal.

* Temperatures: Consulting the ensemble models for temperatures, the 
  GEFS has trended colder while the EC ensemble has trended warmer. 
  The climate percentiles for all ensembles are bottoming out for 
  the lowest temperatures at 850mb Tuesday and further remain in the 
  lowest 5th percentile through the week for high temperatures. 
  Comparing to normal which is around 44F for eastern  Washington 
  for daytime temps, Tues - Fri will see temperatures around 15-18F 
  colder than normal. The NBM would say there is a 25% chance of 
  seeing daytime temps below 28F through the week for Spokane, Coeur 
  d'Alene, Pullman, Moses Lake, Omak, Wenatchee and 35-50% chance of 
  less than 28F for Deer Park, Sandpoint, Bonners Ferry, Republic. 
  Windchill values will dip into the single digits and even some 
  negative values Tuesday morning and similar but slightly warmer 
  Wednesday morning.

* Wind: A surface high develops in British Columbia as the upper Low 
  dives south, resulting in a tighter pressure gradient drapped 
  across Washington and Idaho. Breezy north winds will develop 
  across the Columbia Basin, the Okanogan Valley, and the Purcell 
  Trench. Sustained 12-15 mph with gusts of 20-25 mph will make 
  those cold temperatures even more biting cold. 

* Snow? Some of the ensemble guidance would suggest low 
  probabilities of seeing a weak disturbance Wednesday rotate around 
  the Low as it tracks into the northern Rockies bring measurable 
  snow to the L-C Valley, the Palouse, the Camas Prairie and 
  central/southern Idaho. NBM has 55% probability of measuring snow 
  at Pullman for Wednesday evening. Elsewhere, it looks like a dry 
  forecast. 

Next weekend there are signals of seeing a flat ridge settle over 
the Northwest though models are wildly indecisive at the 
moment. /Dewey


&&

.AVIATION... 
00Z TAFS: Snow is continuing across the Methow Valley and 
Okanogan Valley and is expected to continue through the night. 
Precipitation will spread east this evening and become heavier 
overnight for GEG, SFF, COE, SZT, PUW. Precipitation looks to 
begin as rain or a rain/snow mix for the I-90 corridor and south 
with a transition to snow overnight. Marginal VFR and IFR 
conditions will be possible after 9z through Monday morning. 
Winds will be breezy from the east- northeast for GEG, SFF, COE, 
OMK, and from the east- southeast for MWH, PUW, LWS. vmt

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        25  30  15  30  13  30 /  90  70   0   0  10  20 
Coeur d'Alene  24  29  13  31  14  30 /  80  90   0   0  10  20 
Pullman        31  39  21  35  18  27 /  70  60   0   0  20  20 
Lewiston       36  44  26  38  26  34 /  60  60   0   0  20  30 
Colville       23  29  10  32   4  33 /  90  70   0   0  10  10 
Sandpoint      22  24  12  27  13  28 /  70  90   0   0  10  20 
Kellogg        24  30  11  30  13  29 /  70  90   0   0  10  20 
Moses Lake     30  40  23  34  17  32 /  70  30  20  10  10  10 
Wenatchee      29  34  24  32  18  32 /  80  40  50  10  10  10 
Omak           28  33  18  35  14  34 /  90  70  20  10  10   0 

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Warning from 1 AM to 4 PM PST Monday for Northern 
     Panhandle.

     Winter Weather Advisory from 1 AM to 4 PM PST Monday for Central 
     Panhandle Mountains-Coeur d'Alene Area.

WA...Winter Weather Advisory from 1 AM to 4 PM PST Monday for Spokane 
     Area-Upper Columbia Basin.

     Winter Storm Warning until 10 AM PST Monday for Northeast 
     Mountains-Okanogan Highlands-Okanogan Valley-Waterville 
     Plateau-Western Okanogan County.

     Winter Weather Advisory until 10 PM PST this evening for Central 
     Chelan County-Wenatchee Area-Western Chelan County.

&&

$$