393
FXUS66 KOTX 261034
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...
06Z TAFS: Cooler upper-level trough is tracking into the region
and will promote elevated winds through morning. Pullman has
recently decoupled and added wind shear but this comes with low
confidence and could see increasing surface winds overnight.
Bands of light showers will pass through with the best chance
coming across far SE WA, North Idaho, and the northern mountains.
A Puget sound convergence zone will also impact the Cascade crest
between Hwy 2 and I-90. Clouds with this activity will expand
into Wenatchee but any precip will mainly be confined to
Leavenworth to Stevens Pass. Otherwise, majority of the region
will experience VFR skies with lighter winds on Thursday.


FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate
confidence in VFR conditions for much of the region. The one
uncertainty will be a small shield of MVFR ceilings developing
between Pullman and Spokane. HREF gives this a 20% of occurring.


&&

.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.
&&

$$