314
FXUS66 KOTX 261219
AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 334 AM
PDT Thu Sep 26 2024

.SYNOPSIS...

Temperatures behind yesterdays cold front will push readings closer
to normal values for this time of year. Winds will also be
significantly weaker today. Another system will push through
northern British Columbia late today and overnight bringing some
light rain to locations near the north Cascades. Drier and warmer
weather returns to the region for Friday and Saturday, with
temperatures peaking on Saturday. On Sunday another system will push
through the area bringing breezy winds and cooler temperatures. Some
freezing overnight lows are possible again heading into next week.

&&

.DISCUSSION...

Today and tonight...A distinct upper level trough is currently
passing through eastern Washington and should push into central MT
by mid-morning. Satellite was showing a swath of moisture and
precipitation ahead of its axis with light to moderate showers
depicted over NE WA and the ID Panhandle. These showers should
steadily wane as the trough heads into MT. Model data and current
observations suggest the instability associated with this moisture
is generally too shallow to support thunderstorms early this morning
over our area, however it will remain just deep enough for a few
more lightning strikes over SE BC. Aside from the precipitation
threat early today, the main weather feature will be significantly
cooler temperatures behind yesterdays strong cold front. Yesterday
we saw 850 mb temperatures peaking around 19-22C and todays
forecast shows peak readings in the 10-12C range. This will support
high temperatures in the mid 60s to mid 70s or roughly 15-20F cooler
than what we saw for yesterdays highs and much closer to normal for
this time of year. Winds will also be substantially weaker than what
occurred yesterday as the east-west pressure gradients begin to
relax. West to southwest winds of 15 to 25 mph are still occurring
early this morning, but this should be the peak for the day. The
next weather system is currently taking shape over the Gulf of
Alaska and has a tap to some good sub-tropical moisture. This system
will push a strong low pressure area into northern BC overnight
which will increase the N-S pressure gradients resulting in
increasing southerly flow, late this afternoon and evening
especially for the Okanogan Valley and western Columbia Basin.
Sustained wind speeds could reach the 15-20 mph range with gusts up
to 25 mph. As for precipitation the models are consistent on keeping
all of the Inland NW dry from mid-morning through mid-afternoon.
However the aforementioned moisture will encroach on the north
Cascades late this afternoon and evening and will likely produce
some widespread light rain across western Okanogan and western
Chelan Counties. Totals amounts will range from a trace to 0.05
from Leavenworth to Winthrop with values approaching 0.25 near the
Cascade Crest. Farther east near the Canadian Border there could
also be a small chance (around 10%) of some showers during the
evening, however measurable rain isnt really expected.

Friday and Friday night...Dry zonal or westerly flow is expected
with temperatures rebounding by several degrees. Valley highs should
push into the 70s for most locations with some lower 80s possible
over the LC Valley and Lower Columbia Basin. Winds will generally be
less than 15mph. fx

Saturday to Wednesday: The Inland NW will remain in a progressive
pattern. A couple systems will move by the region during this
period, one around the weekend and the next toward Tuesday night and
Wednesday. However on the weekend the moisture does not sync up with
the best lift and toward Tuesday night and Wednesday the lift is not
as impressive. Look for increase cloud cover Saturday into Sunday,
with shower chances near the Cascades and northeast mountains
Sunday. Then additional shower chances come to the Cascades and the
mountains of WA and ID late Tuesday into Wednesday. About a third of
the models also show some risk coming to the eastern third of WA.
The other two-thirds of the models keep the threat mainly in the
mountains. Either way precipitation amounts look light, with only
about a 10-30% chance of wetting rain (>=0.10 inches) with each
system. The best chances will be near the Cascade crest. Cooler
temperatures heading into next week will also mean some high
elevation snow or a rain/snow mix potential in the Cascades and
north Idaho, with snow levels around 6000-7000 feet next Wednesday,
lowest near the Cascades. Otherwise between systems weak high
pressure will keep things dry and partly cloudy and there could be
some patchy shallow morning fog in sheltered areas.

Winds pick up Sunday as the system is pushing by, with speeds of 10-
20 mph and gusts near 25-35 mph. Locally higher gusts are possible,
especially near the Cascade gaps and downwind of the Blue Mountains.
I did blend the NBM with the 90th percentile winds, increasing them
over the base forecast. A strong jet streams is overhead and there
is good mixing with the passing wave. EFI was showing this to be the
next breeziest day. This will continue to be monitored should winds
need to be increased further. Winds are also forecast to increase
some next Wednesday but not as strong, with gusts near 15-20 mph
possible.

Temperatures are expected to be above normal Saturday, with highs in
the 70s and low 80s. There after temperatures drop to near or
slightly below normal, with highs in the 60s to low 70s. Lows will
be in the 40s and low 50s Sunday morning (maybe some upper 30s in
the sheltered northeast valleys). Then lows will be cooling with 30s
and low 40s and even some upper 20s in the sheltered valleys. The
coldest morning looks like Monday morning and there may be broader
areas of a freeze or frost over the sheltered valley and outlying
areas around the east third of WA and ID. /Solveig

&&

.AVIATION...
12Z TAFS: VFR conditions are expected at all TAF sites through this
period. The main concerns this morning will revolve around some
isolated showers moving through the northern tip of the ID Panhandle
and some residual clouds elsewhere in the Panhandle. These clouds
should remain east of COE and LWS, but brief MVFR cigs could occur
at COE through 15z. Quiet weather will prevail for most of the day,
but an incoming warm front will bring clouds and a small chance of
rain to the north Cascades after 22z and spread mid-level clouds
across much of the region overnight.


FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in
VFR conditions for all TAF sites through this period. The biggest
uncertainty is whether or not MVFR cigs will reform near COE. fx


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        67  49  74  46  80  50 /   0   0   0   0   0   0
Coeur d`Alene  66  48  73  47  79  50 /   0   0   0   0   0   0
Pullman        66  47  72  46  79  48 /   0   0   0   0   0   0
Lewiston       75  53  80  54  86  56 /   0   0   0   0   0   0
Colville       68  39  73  36  76  39 /   0   0   0   0   0  10
Sandpoint      65  43  71  43  76  47 /   0   0   0   0   0  10
Kellogg        64  51  70  51  79  53 /   0   0   0   0   0   0
Moses Lake     70  48  76  44  78  47 /   0   0   0   0   0   0
Wenatchee      71  54  75  50  76  51 /   0  10   0   0   0   0
Omak           72  49  76  47  77  47 /   0   0   0   0   0   0

&&

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

$$