926
FXUS66 KOTX 212125
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
225 PM PDT Sat Sep 21 2024

.SYNOPSIS...

Temperatures will be chilly Sunday morning, promoting frost
formation for many areas and freezing temperatures in the mountain
valleys of northeast Washington. There is a small chance of light
mountain showers in the north Sunday afternoon and evening. A
ridge of high pressure will deliver above normal temperatures
early next week. A more active pattern is expected for the latter
half of next week, with the potential for breezy conditions,
showers, and temperatures returning to near normal.

&&

.DISCUSSION...

Tonight through Monday night: Another chilly night is expected.
Temperatures will overall be a little warmer, but much of the deeper
and sheltered mountain valleys in northeast Washington and the Idaho
Panhandle will see the potential for near freezing temperatures and
frost. Best potential for sub-freezing temperatures will be in the
valleys of the Northeast Mountains that include Colville, Chewelah,
Metalline Falls, Deer Park, Ione, Cusick, and Newport where a freeze
warning remains in effect. These colder, sub-freezing temperatures
will also extend into the northern Panhandle around Priest Lake and
along the west of Lake Pend Oreille that includes the communities of
Athol, Spirit Lake, Blanchard, and Priest River. Most communities
along US-95 in the Northern Panhandle from Porthill to Sandpoint are
expected to remain above freezing, but will see the potential for
frost. Frost is also expect tonight in the valleys of the Central
Panhandle Mountains extending into the Palouse region, including the
communities of Pinehurst, Kellogg, St. Maries, Plummer, Moscow,
Pullman, Rockford, Oakesdale, Garfield, and Colfax.

A weak disturbance moving in on Sunday will result in increasing
cloud cover. This will be followed up be a warm front Sunday night.
The warm front will bring a healthy sub-tropical moisture plume into
the Northwest; however, lack of forcing and dynamical support along
with a very dry near surface layer, will result in little to no
precipitation. There`s only a 10-30 percent chance for measurable
rainfall through Monday at the Cascade crest and over the mountains
right near the Canadian border. Winds aloft won`t be particularly
strong with the upper level jet well north into northern BC resulting
in continued weak winds. The exception will be in the lee of the
Cascades where typical westerly drainage winds into the Wenatchee-
Chelan areas and Waterville Plateau is expected Sunday evening.
Winds will generally be sustained 8-15 with gusts up to around 25
mph though and not of a particular concern.

Temperatures will begin to see a warming trend on Monday with the
western half of the forecast area seeing more of a bump with highs
expected to be in the upper 70s to low 80s. Clouds will be clearing
in the wake of the warm front passage with sunny to mostly sunny
skies. Further west, the temperatures are expected to be in the low
to mid 70s in the Idaho Panhandle. /SVH

Tuesday through Saturday: Tuesday and Wednesday will be the last
days of warm, dry conditions as the ridge begins to breakdown.
Increasing clouds are expected through the day as a trough begins to
press into the Pacific Northwest. While the trough will increase the
moisture, much of the lowlands will not benefit from any precip. The
precip will mainly rain showers over the mountains starting
Wednesday afternoon. Some of the very high peaks of the Cascades
could receive light snow. There is also a weak chance of an isolated
thunderstorm along the Canadian Border and Cascade Crest. Another
concern is the winds and RHs across the Basin as the ridge breaks
down. Ensembles are showing an increase  probability of low
RH/breezy winds Wednesday afternoon. It is increasing concern for
fire starts and spread. Highs for these days will be in the upper
70s and 80s. Overnight lows will be in the upper 40s and 50s.

Thursday through Saturday: The region will be under a zonal flow
pattern for for the rest of the period. While models indicate
shortwaves passing through the region, the rain shadow effect will
continue to keep the Basin mainly dry with continue showers over the
higher terrains. Highs will dip into the 50s and low 60s for highs.
Overnight lows will be in the upper 30s and 40s for most. A few cold
pockets in the northern valleys could hit freezing overnight. /JDC

&&

.AVIATION...
18Z TAFS: VFR conditions will prevail. Bands of mid and high
clouds will move over the region into Sunday with light winds.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence
for VFR conditions. /SVH.

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        42  75  46  76  50  83 /   0   0   0   0   0   0
Coeur d`Alene  36  73  47  74  50  81 /   0   0   0   0   0   0
Pullman        39  71  45  71  48  80 /   0   0   0   0   0   0
Lewiston       47  78  55  79  55  87 /   0   0   0   0   0   0
Colville       30  72  38  77  41  82 /   0  10   0   0   0   0
Sandpoint      36  71  43  71  47  77 /   0  10  10   0   0   0
Kellogg        39  68  49  70  52  79 /   0   0  10   0   0   0
Moses Lake     44  78  48  79  50  84 /   0   0   0   0   0   0
Wenatchee      53  78  56  80  58  82 /   0  10   0   0   0   0
Omak           47  77  51  83  55  85 /   0  10   0   0   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Frost Advisory until 8 AM PDT Sunday for Central Panhandle
     Mountains-Idaho Palouse-Northern Panhandle.

WA...Frost Advisory until 8 AM PDT Sunday for Washington Palouse.

     Freeze Warning until 8 AM PDT Sunday for Northeast Mountains.

&&

$$