949
FXUS66 KOTX 180944
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
244 AM PDT Wed Sep 18 2024

.SYNOPSIS...

Isolated light rain showers will persist over north Idaho through
early this morning. Conditions will trend drier toward the end of
the work week, then light rain chances mainly for the mountains
Sunday into Monday. A ridge of high pressure will deliver above
normal temperatures early next week.

&&

.DISCUSSION...

Today through Friday night: Lingering showers will continue in the
Idaho Panhandle through the morning, before the system shifts
eastward, drying the region out by the afternoon. As the coastal
system continues to drop south through Thursday, the PacNW will
remain in a more zonal flow. With this zonal flow, expect quieter
weather with temperatures near seasonal normals (highs in the 70s
and lows in the upper 40s to low 50s), dry, and lighter winds.
Friday brings more sunshine and a gradual cooling trend, with
temperatures 2 to 5 degrees cooler than previous days. /KM

Saturday through Wednesday: There is good agreement amongst the
model ensembles for the general weather pattern in the extended part
of the forecast. The general consensus is for a warm front to push
across the Northwest late Sunday into Monday. Within the warm sector
will be a healthy plume of moisture directed into the region with P-
wats of over an inch. What appears to be lacking is dynamics aloft
and instability to ring out that moisture. The parent low looks to
remain well away from the Inland Northwest in the Gulf of Alaska.
Main forcing mechanism will be some weak moist isentropic ascent and
orographics. Precipition will be favored over the mountains and
specifically across the Cascade crest and into the Idaho Panhandle
with flow aloft out of the northwest. The National Blend of Models
(NBM) is probably under doing the precipitation potential over the
mountains as P-wats will be between 150-180% of normal. It won`t
take too much to get moisture to precipitate out, and sometimes
model guidance will underplay this potential in scenarios like this
where dynamics is weak. In any event, clouds look to increas and
thicken Sunday into Sunday night with mostly cloudy skies continuing
into at least early Monday.

Ridging of high pressure then builds in over the region for Tuesday
with what looks to be a fairly sharp bump up in temperatures going
from low to mid 70s Sunday into Monday into the upper 70s to low 80s
by Tuesday. Wednesday may also be a mild day, but there is more
uncertainty toward the end of this period. The model ensemble
cluster analysis suggests a 40-45% chance for a cold front to sweep
across on Wednesday. This would bring breezy to windy conditions.
The cold front may not bring much in the way of precipitation
either with a mild concern for elevated fire weather conditions
around this time. There is another 30% of the ensembles that
shows a weaker cold front passage and is delayed that would
suggest either a Wednesday night or Thursday timing for frontal
passage. Then around 25% of the ensemble clusters that suggests a
scenario where the ridge holds firm and the region continues a
warming and drying trend further. This quarter of the ensemble
members suggests a warmer solution, particularly so west of the
Cascades but also across eastern Washington and into the Idaho
Panhandle. There is high confidence that we aren`t looking at a
wetting rain scenario with below normal temperatures. The extended
looks at least near average or above average for temperatures.
/SVH

&&

.AVIATION...
06Z TAFS: Light showers will continue through 07-09z from near
KSFF/KCOE south to near KPUW. Not much impact from these for the
TAF sites, although will be monitoring the potential for IFR
stratus Wednesday morning due to a moist boundary layer and
upslope boundary layer winds into KGEG/KSFF/KCOE. Current
probabilities are under 50% at these TAF sites so prevailing
conditions were kept VFR. Any stratus that develops will lift and
erode by 17-18z, with flat stratocumulus in the afternoon.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: HREF model shows a
60-70% chance of IFR stratus between 12-16z south of Spokane
(Cheney, Spangle areas), decreasing to a 40% chance over GEG, with
a 20% chance at KSFF/KCOE. With favorable low level winds and some
light showers further moistening the boundary layer these
probabilities seem reasonable. JW

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        76  49  76  46  72  44 /   0   0   0   0   0   0
Coeur d`Alene  73  49  74  47  70  43 /   0   0   0   0   0   0
Pullman        69  44  73  45  66  40 /  10   0   0   0   0   0
Lewiston       77  54  81  53  75  49 /  10   0   0   0   0   0
Colville       78  39  76  37  71  35 /   0   0   0   0   0   0
Sandpoint      71  45  71  44  68  39 /   0   0   0   0  10  10
Kellogg        68  49  72  49  65  45 /  10   0   0   0  10  10
Moses Lake     79  46  79  46  73  43 /   0   0   0   0   0   0
Wenatchee      80  54  79  54  73  49 /   0   0   0   0   0   0
Omak           83  51  81  48  75  46 /   0   0   0   0   0   0

&&

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

$$