083 
FXUS66 KOTX 061132
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
332 AM PST Sun Nov 6 2022

.SYNOPSIS....

The next winter storm will bring snow into north-central 
Washington today. 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...

Today and Monday:
Convective rain and snow in NE WA and N ID have mostly moved out
of the area. A compact mesoscale shortwave provided forcing for
ascent and favorable low level thermodynamics allowed for some
beefy convective rain and snow showers with graupel. Radar 
estimated QPE shows a small bullseye over a tenth of an inch over 
Schweitzer Mountain. Radar imagery has shown some transient bands 
of showers in southern WA as well. HRRR/HiRes-FV3 seem to be 
handling this area of rain and snow showers the best currently 
with lighter coverage then the ARW. Nonetheless, forecast 0-2 km 
AGL mean RH, wind and theta-e lapse rates support convective rain 
& snow showers through 4 AM. Winds have finally calmed down as the
atmosphere has decoupled in most locations except the Palouse and
Southern WA where low level instability remains. Details with the
incoming snowstorm are below.

*Strong upper level low to bring significant snow accumulations 
 to Eastern Washington and north Idaho today and tomorrow*

Strong synoptic lift and southerly 500mb flow and low level 
southeast winds will make for a potent snowfall event for north 
central Washington. One area of great uncertainty is the US-2 
corridor through Wilbur, Creston, and Almira. A tight snowfall 
gradient will occur as southern locations will receive less than an 
inch while locations just 25 miles north will see accumulations 
above 6 inches. Wenatchee is seeing higher totals as well, but am 
not confident in this given the high certainty of the warm conveyor 
belt keeping them warm enough for lower end accumulations. Winter 
Storm Warnings look good and will be in effect from 4am Sunday 
through 10 AM Monday. Omak snow totals have been bumped to better 
reflect the latest global ensemble guidance around 12 inches. This 
is still below ensemble means but the warmer temperatures this 
afternoon will lead to lower snow ratios and compaction of the 
morning snowfall. Additional highlights are being discussed for sub 
warning criteria snowfall & flash freezing of rainfall behind the 
arctic front. Point snowfall forecasts can be found at 
weather.gov/spokane.

Timing: Precipitation will spread east through the day today with a 
change to rain or a rain/snow mix as temperatures warm above 
freezing for the Wenatchee area, the Basin into the Spokane area, 
Palouse and southward. Stevens Pass and Loup Loup Pass will see the 
snow starting now through the next few hours as coverage increases. 
Sherman pass will start to see snow by noon or so according to 
guidance. Snow levels will increase to 1700 feet or so by 4 PM this 
afternoon but rapidly fall to the surface overnight in the northern 
counties with the arctic front passage. The transition to all snow 
will occur late this evening as the front begins to push south. 
Snowfall will ramp down Monday morning for the Okanogan Highlands 
and Monday afternoon for northern Idaho. A secondary wave will
bring additional accumulations to the Cascades/Okanogan Highlands
Monday afternoon. Accumulations are uncertain at this point but an
additional couple inches is plausible in the lowlands. 

Snow intensity: Synoptic lift is strong and HREF guidance is hinting 
at greater than 70 percent probs of several hours of 1 inch snowfall 
rates today and tonight. This makes sense given several hours of 
strong isentropic lift from the 290-300K theta surfaces, favorable 
upslope flow, and 2+ inches of QPF in 36 hours in north central 
Washington. The Cascades and Okanogan highlands will first 
experience these snowfall rates through this morning then the higher 
elevations of Idaho this afternoon.

Highs on Monday will be much colder with the Arctic front passage 
with highs dropping into the 20s to mid 30s and lows in the teens to 
low 20s with single digits across our northern valleys. Breezy 
northeast winds will result in very cold wind chills Monday morning. 
Lows Monday night will be quite cold in the single digits in N ID to 
low 20s in the lower Basin. /Butler

Tuesday through Sunday: A cold upper-level trough will remain over the 
Western US Tuesday but the Inland Northwest will remain void of 
any shortwave energy as the Polar Jet digs southward into 
California. A robust pressure gradient between low pressure to our
south and a cold Canadian high to our northeast will create 
blustery north to northeasterly winds across the forecast area 
throughout Tuesday and to a lesser degree...Wednesday. Sustained 
winds of 10-15 mph with gusts of 25 mph will be common across the 
Columbia Basin, Purcell Trench, and Okanogan Valley. With 
afternoon highs only expected to top out in the lower 30s...be 
prepared for biting wind chills in the teens and twenties during 
the afternoon then teens to near zero or colder overnight. We will
see increasing clouds by Tuesday night as midlevel warm air 
advection brings an influx of moisture into southeastern WA and 
the lower Idaho Panhandle. NBM, ENS, GEFS all introduce 30-50% 
precipitation chances around the Blue Mountains, Camas Prairie, 
L-C Valley, and into the Palouse and Central Panhandle Mountains. 
The ENS is the most aggressive model with the precipitation with 
several members expanding precipitation chances as far north as 
Spokane-Cd'A and Bonners Ferry. This does not have a lot of 
support from the other ensemble models but will need to be watched
in the coming days as most precipitation types by this point will
be snow. Our drier model guidance is barely producing a few 
hundredths of liquid but several ENS members support a tenth so 
this could be the difference of a dusting of snow to as much as an
1-1.5" following the wetter ENS.

Thereafter, the region will get a well needed break from the active 
weather pattern as high pressure settles into the Northwestern US
from Thursday into Saturday. This stable weather pattern 
following a few days of wet/snowy weather is a good setup for 
below normal temperatures within the valleys and potential for low
clouds and fog, especially overnight and morning. Models tend to 
struggle with temperatures in these patterns. Locations with fresh
snow that experience clear skies in the evening will likely 
radiate very rapidly and experience lows in the teens or even 
single digits. The low November sun angle typically cannot provide
enough heating to fully mix out these inversions in the 
afternoon. However, if there are other layers of clouds present 
which is a strong possibility, it will be significantly warmer at 
night but continued cooler than normal in the afternoon with 
afternoon temperatures remaining in the 30s. All things 
considered, we see large spreads with the ensemble temperature 
forecast, sometimes on the order of 8-10 degrees for any 
individual MaxT/MinT point. Confidence in the forecast begins to 
tumble by mid to late weekend as the ridge starts to flatten. 
Roughly 40% of a 100 member ensemble system bring an influx of 
moisture in the region bringing our next chance for snow. Stay 
tuned. /sb

&&

.AVIATION... 
12Z TAFS: Strong upper level low will spread precipitation into 
the Cascades in the next hour and into Wenatchee, Chelan, and Omak
between 14-17z. High confidence cigs will dip below IFR at EAT 
with light to moderate snow begins. Temps will rise and change to 
rain/snow mix then rain at EAT later this morning but cigs will 
remain low. Precip will shift eastward through the day but 
confidence is low- moderate on timing/intensity of the showers, so
VCSH groups are the prevailing weather group for GEG, SFF, COE. 
An arctic cold front will change precip type to snow overnight for
COE, SFF, GEG, PUW, EAT. MVFR conditions will prevail for those
sites with lower cigs but a moderate burst of snow could induce 
IFR conditions briefly. MWH/LWS has rain as the dominant weather 
type overnight, but a brief period of snow may occur overnight as 
the arctic front passes through. Gusty winds up to 25 kt may occur
with tight pressure gradients today and with the passage of the 
cold front. Confidence is moderate in gusts exceeding 20 kt during
the day and high with the arctic front passage overnight. Butler 

Butler

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        42  26  29  14  30  14 /  30  80  60  10   0  10 
Coeur d'Alene  41  25  28  14  31  16 /  20  60  80   0   0   0 
Pullman        42  33  38  17  35  16 /  20  80  60  10   0  10 
Lewiston       50  37  44  26  38  25 /  10  60  50  10   0  10 
Colville       34  22  28   4  32   4 /  60  80  70  10  10   0 
Sandpoint      36  24  26  12  27  13 /  30  60  90   0  10   0 
Kellogg        39  26  31  11  30  14 /  20  40  90   0   0  10 
Moses Lake     42  33  37  21  34  14 /  60  70  30  20  10  10 
Wenatchee      37  30  34  23  32  17 /  70  70  30  20  10   0 
Omak           33  28  32  17  35  14 /  80  90  60  20  10   0 

&&

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

&&

$$