Harrington, Washington Weather Forecast Discussion

505
FXUS66 KOTX 271729
AFDOTX
Area Forecast Discussion
National Weather Service Spokane WA
1029 AM PDT Sat Sep 27 2025
.KEY MESSAGES...
- Warm and dry weekend.
- Areas of haze and smoke impacting air quality across the
  region.
- Unsettled weather pattern next week with chances for showers.
&&
.SYNOPSIS...
Temperatures trend warmer for this weekend with highs in the
upper 70s to mid 80s by Sunday. Cooler temperatures and chances
for showers for the first half of next week.
&&
.DISCUSSION...
Saturday-Sunday: A few changes coming in the next 48 hours as a
deep low begins to drop southward from the Gulf of AK and
heights increase downstream over the Inland NW. The building
ridge will be flat today as one more weak disturbance slips
through central British Columbia. The trailing frontal band will
remain nearly stationary over Vancouver Island with light rain
skirting the Olympics but little more than passing mid and high
clouds for northern Washington and North Idaho. Winds will react
to this weak system coming out of the south and southeast with
generally light speeds. Main area for winds nearly 10 mph and
gusts around 15 mph will be within the Okanogan Valley where the
weak gradients will align with the diurnal wind patterns. Smoke
coming from the Cascade fires will likely remain near the
Cascades and drift to the north and northwest with less impact
to Eastern WA and N Idaho though areas of haze and high level
smoke that arrived Friday night may have hard time completely
scrubbing out. The southerly flow will result in warm air
advection and temperatures climbing back into the 70s to 80s. On
Sunday, the ridge will amplify further as a deep low continues
to carve into the Eastern Pac. Temperatures continue to warm
reaching the lower 80s for valleys under sunny skies. Light
diurnal driven winds in the morning will increase from the south
in the afternoon with afternoon breezes around 15 mph. Looking
for a period of dry conditions for early fall projects or just
want to enjoy the outdoors, may want to take advantage of this
weekend.
Monday-Thursday: Models remain in good agreement of the first
fall-like weather system arriving next week delivering periods
of showers, cooler temperatures, breezy conditions, and small
threat for thunderstorms. A broad upper-level trough will slowly
come inland starting on Monday with a moisture laden frontal
band moving into Central WA through the day. Clouds will thicken
but any precipitation will likely be very light as it will take
time to moisten the air mass. The combination of virga and cool
air advection will allow for increasing south to southwest
winds with gusts 15-25 mph. A second band of light showers is
also showing up in the vicinity of far SE WA and the lower Idaho
Panhandle with the highest probabilities south of a line from
Lewiston to Mullan Pass.
Monday night and Tuesday, a vigorous low pressure system will
setup off over the Gulf of AK then slowly fill and migrate
southeast into the Pac NW Wednesday and Thursday. Energy
rotating around the offshore low will get slung inland
delivering increasing chances for showers and a few
thunderstorms. While the shear is very impressive, the CAPE is
meager so main thunderstorm threat looks to be embedded
lightning strikes at this time but will need to keep a close eye
on far SE WA and Idaho Panhandle for the instability parameters
higher than forecast. This activity looks to come through in
clusters of light to moderate showers with rainfall amounts
varying from a few hundreths to around a quarter of an inch. If
any areas were to receive two or three of these clusters of
precipitation, it is conceivable that rainfall amounts by
Thursday surpass half an inch. Confidence however, is not
stellar exactly where these clusters will track through and they
will be moving at a decent clip with upper-level winds of
30-40kts early in the event then slower by Wednesday into
Thursday as the weakening low comes inland. What can be said,
given the position of the offshore low, the low-level flow will
be from the southeast and closer to south around 700 mb. This is
great news for the East Slopes of the Cascades and ongoing
fires which will have a chance for rain and not contending with
rain shadowing common with systems sweeping inland with westerly
flow. However, clusters of rain will still need to setup along
the perfect longitude while tracking south to north for these
fires to receive a soaking rain and this comes with a lot of
uncertainty. Turning toward 48 hour probabilities for at least
0.20" from ensemble suites, most of the mountains from North
Idaho, across northern WA, and into the East Slopes come with a
50-80% chance. There is a tight gradient across East Slopes
starting near 90% along the crest and decreasing to 40% along
the Hwy 97 corridor with the gradient intersecting the Lower
Sugarloaf and Labor Mountain Fires. I think these higher
probabilities are being driven by the ENS members which are
significantly wetter vs the GEFS. All things considered, the
pattern looks favorable for most areas to receive a tenth of
rain over the multi-day event but early prognosis for season
ending rains looks more localized than widespread at this time.
Friday into next weekend: The remnants of the low will be
departing to the east on Friday with additional showers found
across southeastern WA and the Idaho Panhandle. There is
significant uncertainty how the pattern will evolve over the
weekend and into early next week. Seems to be moderate
confidence for a period of ridging and another trough but timing
and orientation of these waves comes no confidence. If the
ridge were to amplify off the coast, could be dealing with a
much cooler system dropping in from the northwest tapping into
cooler air coming down from the northern latitudes this has
support from 40-50% of the ensembles. The other 50 percent have
the ridge over west or slightly inland indicative of warm and
dry or warmer and spotty showers. Hard to trust any solution or
have confidence how this will play out. /sb
&&
.AVIATION...
18Z TAFS: VFR conditions to continue through the period though
smoke will be the primary concern with winds trending lighter
lowering mixing heights.
FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Low confidence for MVFR or worse conditions from wildfire smoke.
-----------------------
Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance
For additional probabilistic information for NWS Spokane
airports, please refer to the Aviation Dashboard on our webpage:
https:/weather.gov/otx/avndashboard
&&
.Preliminary Point Temps/PoPs...
Spokane        79  49  82  54  73  52 /   0   0   0  10  10  40
Coeur d`Alene  79  51  83  55  76  53 /   0   0   0  10  20  50
Pullman        78  49  82  53  72  49 /   0   0   0  10  20  60
Lewiston       82  54  86  60  79  57 /   0   0   0  10  20  60
Colville       73  38  80  43  73  42 /  10   0   0  10  30  50
Sandpoint      73  45  79  49  72  48 /   0   0   0  10  30  50
Kellogg        77  55  84  59  73  54 /   0   0   0  10  40  60
Moses Lake     79  47  80  52  74  49 /   0   0   0  10  20  30
Wenatchee      76  55  79  58  72  52 /   0   0   0  20  40  40
Omak           76  49  81  54  75  51 /  10   0   0  10  30  50
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
WA...Air Quality Alert until noon PDT Sunday for Central Chelan
     County-Okanogan Valley-Waterville Plateau-Wenatchee Area-
     Western Chelan County.
ID...None.
&&
$$

NWS OTX Office Area Forecast Discussion