721
FXUS66 KOTX 211803
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1103 AM PDT Sat Sep 21 2024

.SYNOPSIS...

Temperatures will be chilly this morning, and again Sunday
morning, promoting frost formation for many areas and freezing
temperatures in the mountain valleys of northeast Washington. Dry
conditions continue into Sunday. 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.

&&

.UPDATE...
Portions of the frost advisory expired this morning.

&&

.DISCUSSION...

Thicker clouds are expected to move into the region east of the
Cascades tonight. This will promote warmer overnight temperatures
for areas closer to the Cascade Mountains. Temperatures will also
be a little warmer over the Columbia Basin and across the
Spokane/Coeur d`Alene corridor. Frost formation is not expected
to be as widespread for these areas tonight. /SVH

&&

.PREV DISCUSSION... /issued 306 AM PDT Sat Sep 21 2024/

Today through Sunday night: A dry seasonal westerly flow aloft
prevails across the Inland NW through the weekend. A few weak
upper level disturbances track will track through the flow. The
atmosphere is quite dry especially with dewpoints in the mid 20s
to mid 30s. Under weak surface high pressure, surface winds are
light and temperatures continue to drop. Currently, most regional
temperatures are running 7 to 19 degrees cooler than yesterday at
this time. Temperatures have already reached the middle 30s in
Deer Park and Sandpoint. Areas of frost and local freezing
temperatures look likely across parts of extreme eastern WA into
the northern Panhandle. The current early season Freeze Warning
and Frost Advisories will remain in effect through mid morning.
This looks to be the coldest morning of the week.

Anticipate an increase of mid and high clouds by this afternoon
as a weak shortwave ripples through the region. Not expecting
precipitation as the lower levels remain dry. Afternoon
temperatures should be up a couple degrees compared to Friday and
close to seasonal normals, while winds remain light. Skies should
clear by evening, although high clouds increase from the northwest
by Sunday morning. Radiational cooling will be pronounced across
extreme eastern WA and the ID Panhandle. Overnight temperatures
are expected to take another nose dive with a return to near
freezing readings across the valleys of northeast WA, north Idaho,
and parts of the Palouse.

The next shortwave passes through the region on Sunday and skies
remain overcast for much of the day. This feature may lead to a
few light showers with a 10-20% chance across the northern
mountains Sunday afternoon and evening. West-southwest surface
winds increase Sunday afternoon with gusts of 15-20 mph in the lee
of the Cascades to the Columbia Basin. Despite the cloud cover,
daytime temperatures are expected to warm a few more degrees with
widespread 70s to lower 80s. /rfox.

Monday to Friday: A ridge of high pressure builds over the Pacific
Northwest, before the next trough moves in toward the second half
of the week. Expect dry and weather through Tuesday. Then a trough
moves in and the onshore flow increases. This will bring shower
chances to the Cascades Wednesday, then across the northern
mountains Wednesday night into Thursday. About 65% of the
solutions favor this depiction, while the other 35% bringing
chances to the eastern third of WA and lower ID too. So PoPs will
need to be adjusted higher should the solutions start to trend
wetter. Thereafter models continue to show a more progressive
flow, but they diverge over the evolution of disturbances moving
in. Shower chances will continue around the mountains and near the
WA/ID border heading into Friday.

Overall precipitation will be in the form of rain, but some
higher mountain snows are possible starting late Wednesday night
continuing into Friday over the Cascades. Away from the Cascades
precipitation amounts are expected to be light. In the Cascades,
the 24-hour probabilities of wetting rain 40-80%, with the higher
probability near the immediate crest and around mid-week. Any snow
that may fall there is expected to be light, with ensemble
showing 24-hour probabilities of >=1 inch only near 10-20%.

These incoming waves will also bring increased winds, with gusts
near 15-25 mph each afternoon between Wednesday and Friday. If any
of these waves are a bit stronger those winds may also be a bit
stronger. Temperatures will reach the 70s to low 80s Monday, then
rise into the upper 70s and 80s Tuesday and Wednesday (about 10
degrees above normal). Then temperature cool closer to seasonal
norms and by next Friday night (into next Saturday morning)
overnight lows near freezing will possible in similar places at
they are this morning. Lastly we can`t rule out some patchy fog in
sheltered valleys, but this is expected to be isolated. /Solveig

&&

.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        72  41  75  46  76  50 /   0   0  10  10   0   0
Coeur d`Alene  70  40  73  47  74  50 /   0   0  10  10   0   0
Pullman        69  39  71  45  71  47 /   0   0   0   0   0   0
Lewiston       75  47  78  55  78  55 /   0   0   0   0   0   0
Colville       72  33  72  36  76  41 /   0   0  10  20   0   0
Sandpoint      71  37  71  43  71  47 /   0   0  10  10   0   0
Kellogg        67  42  68  49  70  52 /   0   0   0   0   0   0
Moses Lake     75  43  78  48  79  51 /   0   0   0   0   0   0
Wenatchee      75  52  78  56  79  59 /   0   0  10   0   0   0
Omak           76  47  77  51  81  54 /   0   0  10  10   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.

&&

$$