282 
FXUS66 KOTX 092106
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
206 PM PDT Sat Oct 9 2021

.SYNOPSIS...
The next weather system will bring a chance of rain tonight
becoming likely in the Idaho Panhandle Sunday morning. Light snow
is likely for the Cascade passes by Sunday morning. Breezy winds 
will also develop followed by cooler temperatures. This bout of 
cool will likely lead to widespread freezes across most valley 
locations. Drier weather is expected on Tuesday before a weak 
weather system brings a chance of precipitation on Wednesday.

&&

.DISCUSSION...
Tonight through Sunday night: A 110kt upper level jet will sag
southeast over the region tonight sending a cold front quickly
across the region. Initially a weak warm front will reach the
Cascades late this evening with rain developing near the Cascade
crest. The cold front will reach the Cascades late tonight, before
reaching the Idaho Panhandle Sunday morning. Snow levels in the
Cascades will drop from 7000 feet this evening to 3500 feet Sunday
morning. Moist and unstable westerly flow behind the cold front
will likely produce showers into the Cascade crest with snow
expected for Stevens Pass. Given the warmer road temperatures any
accumulation is expected on grassy surfaces with up to 2 inches
possible by Sunday evening. With a possible Puget Sound 
Convergence Zone in the morning near Stevens Pass some brief 
higher snow intensity is possible. 

Behind the cold front a colder air mass moves in with 500mb temps
falling to near -30C Sunday afternoon which will aid in 
destabilizing the atmosphere. Although on the flip side to the 
increased instability will be drying behind the front with model 
dewpoints dropping into the upper teens and 20s over much of 
Eastern WA/N Idaho. This should limit post-frontal shower activity
except near the Cascade crest, Canadian border, and over the 
Idaho Panhandle. Model soundings show graupel possible out of the 
convective showers, with cloud temperatures likely too cold for 
lightning. 

The other story will be the windy conditions behind the front as 
pressure gradient tighten, producing wind gusts of 30-35 MPH 
across the Columbia Basin, Blue Mountains, Palouse, West Plains, 
and on ridgetops. Patchy blowing dust is possible, but recent 
rains leads to lower confidence of any significant visibility 
restrictions. 

Sunday night the showers will die off with the loss of daytime 
heating. Clearing skies, winds becoming light, and low dew points 
will mean another cold night for the region with widespread frost 
by morning with another hard freeze for similar locations that 
dropped in the 20s this morning.  JW

Monday: The trough will dig deep into the Great Basin. Patchy 
valley fog will burn off across NE WA and the ID Panhandle through
the morning. Cooler northerly flow will prevail in the post 
frontal environment. Winds down the Okanogan Valley and into the 
western Columbia Basin will bring gusts 15-20 mph. Temperatures 
will also be cooler...in the 50s, which is 6-10 degrees below 
average. Ensembles are suggesting some mountain showers in the
afternoon across Idaho. Otherwise all other locations will be
seeing drier air rapidly move in providing sunny skies.

Monday Night and Tuesday: Skies will be clear with fairly minimal
fog development. This will allow temperatures to drop to the
coldest readings in the 7 day forecast. Temps in the 20s is
expected for most locations, but some typically colder northern 
valleys could see upper teens and some spots around Wenatchee and 
Lewiston could be at or slightly above freezing. Clouds will start
to increase late Tuesday in the afternoon ahead of the next 
weather system.

Tuesday Night through Wednesday Night: The next trough will move
through the region. EC and GFS ensemble models are still showing
more precip than what the NBM is. The onset of precip looks to be
a bit slower than what it was showing yesterday. Tuesday night 
mountain snow and valley rain or possibly mixed with snow is 
expected for the Cascades. Then around sunrise it will move east. 
This is the period of greatest uncertainty. Will the precip reach 
the ground after the dry conditions Monday & Tues? Currently there
is a slight chance of rain or snow for eastern WA and portions of
N ID, albeit the chance and confidence is currently low. Latest 
ensemble timing bring the best chance of precip through during the
afternoon and evening hours and have increased chance of precip 
for portions of E WA/N ID. We could also see some breezy winds, 
but currently they look to be 20 mph or less. Snow levels will be 
lowering through the night with snow down to 3000-3500 ft. So some
mountains in the ID Panhandle could see light snow by Thursday 
morning.

Thursday through Saturday: A little bit more uncertainty during
this period. We look to be under a westerly or southwesterly flow
ahead of another trough that moves out of the Gulf of Alaska and
towards the region sometime next Sunday/Monday. Other than some
isolated showers mainly across the Cascades and portions of north
ID expect some benign weather. Temperatures start rebounding up
Thursday and by Sunday we will be right around average for the
middle of October...mid 50s to lower 60s. /Nisbet


&&

.AVIATION...
18Z TAFS: Clouds will increase across the region through tonight
as a cold front approaches and then tracks across the area. A
brief period of rain is possible with the front mainly between
9-15z Sunday, with areas of MVFR conditions mainly over the ID
Panhandle and eastern third of WA. Central WA will be in the rain
shadow with continued VFR conditions forecast. Southwest winds
will be locally gusty this afternoon ahead of the cold front.
West-southwest winds will increase Sunday morning region wide 
behind the cold front with gusts 15-25 kts, locally to 30 kts 
forecast mainly after 14-15z Sunday. JW

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        42  57  31  53  28  54 /  40  30   0   0   0   0 
Coeur d'Alene  42  54  31  52  28  54 /  50  60   0  10   0   0 
Pullman        41  54  30  49  26  51 /  30  50  10  10   0   0 
Lewiston       47  61  38  55  34  57 /  20  30  20  10   0   0 
Colville       39  57  26  54  19  56 /  50  20   0   0   0   0 
Sandpoint      40  52  29  49  24  51 /  60  60  10  10   0   0 
Kellogg        42  50  31  49  31  51 /  40  90  10  20   0   0 
Moses Lake     44  62  31  57  28  56 /  30   0   0   0   0   0 
Wenatchee      45  58  36  57  34  56 /  30   0   0   0   0   0 
Omak           40  62  29  59  29  58 /  30   0   0   0   0   0 

&&

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

&&

$$