845
FXUS66 KOTX 210429
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
929 PM PDT Fri Sep 20 2024

.SYNOPSIS...

Temperatures will be chilly overnight tonight into Sunday morning
promoting frost formation for many areas and freezing temperatures
in the mountain valleys of northeast Washington. Dry conditions
will continue into Sunday. A small chance for light rain mainly
over the mountains Sunday night. 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 Sunday: The Inland Northwest will be under a dry
northwest flow pattern with dew points dropping down into the low
20s and low teens for a few spots. Breezy north to northwest winds
bringing in the dry polar continental air mass will relax through
the evening hours. There is some moisture aloft moving into the
central Washington Cascades that may spread cirrostratus cover
from Wenatchee to Moses Lake, but much of the northwest portion of
the region is expected to just see thin high cirrus clouds, and
it doesn`t appear that these clouds will do much to trap
terrestrial radiation to keep surface temperatures from plummeting
overnight in the dry air mass. Deeper, sheltered mountain valleys
particularly from the Okanogan Highlands over to the Idaho
Panhandle should radiate out well overnight as the winds relax. I
expect temperatures in these valleys to drop quickly into the 30s
and a substantial portion of these valleys dip into the low to mid
30s (e.g. Republic, Metalline Falls, Colville, Chewelah, Deer
Park, Newport, Priest River, Athol, Sandpoint, St. Maries, and the
Silver Valley). The northern portion of the Upper Columbia Basin,
Spokane Area, Coeur d`Alene Area, and Palouse will see the
potential for lows in the mid 30s. Chances look favorable for a
widespread frost/freeze and anyone with sensitive vegetation
should take action to cover plants or bring them indoors to
protect them from damage. There is a better potential for cloud
cover pushing across the Cascades Saturday and the air mass
slightly warmer aloft for Saturday night. Low temperatures by
Sunday morning look to be chilly again for the eastern third of
the forecast area at least, but looking to be 2-4 degrees warmer
than tonight. The freeze warning for the Northeast Mountains
covers the overnight period for tonight and Saturday night with
frost advisories in the Idaho Panhandle and Palouse in effect for
both nights as well. The Okanogan Highlands, Columbia Basin,
Spokane Area/Coeur d`Alene Area should see temperatures mild
enough overnight Saturday that frost doesn`t look to be a threat.

Sunday night through Wednesday: A weak shortwave disturbance
pushes across late Sunday. This will bring increasing clouds, but
with low levels of the atmosphere so dry, it is unlikely that we
will see much precipitation, if any. A warm front pushes across on
Monday and this will pump up a high pressure ridge for Tuesday.
Temperatures Tuesday into Wednesday will warm up above normal
with highs in the upper 70s to low 80s. There continues to be
uncertainty with how this ridge will break down. The latest
ensembles are now trending toward a quicker break down around
Wednesday into Thursday, and bringing through a cold front.
Somewhere in the neighborhood of 40% of the ensembles supports
this scenario; although, there are varying degrees of strength of
the cold front passage. I went ahead and kept what the National
Blend of Models (NBM) is forecasting, but a stronger cold front
passage would support higher probability for showers and breezy
winds. Confidence is increasing that temperatures return to normal
at the end of next week, and the break down of the ridge will
introduce the possibility for shower chances. /SVH

&&

.AVIATION...
06Z TAFS: Bands of mid and high clouds will move over the region
into Saturday with light winds. This will result in continued in VFR
conditions. JW

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence
for VFR conditions through Saturday. JW

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        37  72  41  74  46  74 /   0   0   0   0  10   0
Coeur d`Alene  38  70  40  71  47  72 /   0   0   0   0  20   0
Pullman        38  68  39  71  45  70 /   0   0   0   0  10   0
Lewiston       45  75  47  77  55  78 /   0   0   0   0  10   0
Colville       33  71  33  72  36  75 /   0   0   0  10  20   0
Sandpoint      35  68  37  68  43  70 /   0   0   0  10  30   0
Kellogg        38  67  42  68  49  68 /   0   0   0   0  30  10
Moses Lake     40  74  43  77  48  77 /   0   0   0   0   0   0
Wenatchee      49  75  52  78  57  78 /   0   0   0   0   0   0
Omak           43  75  47  78  51  79 /   0   0   0   0   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Frost Advisory from 2 AM Saturday to 8 AM PDT Sunday for Central
     Panhandle Mountains-Idaho Palouse-Northern Panhandle.

     Frost Advisory from 2 AM to 8 AM PDT Saturday for Coeur d`Alene
     Area.

WA...Frost Advisory from 2 AM Saturday to 8 AM PDT Sunday for
     Washington Palouse.

     Frost Advisory from 2 AM to 8 AM PDT Saturday for Okanogan
     Highlands-Spokane Area-Upper Columbia Basin.

     Freeze Warning from 2 AM Saturday to 8 AM PDT Sunday for
     Northeast Mountains.

&&

$$