075
FXUS66 KOTX 291202
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
502 AM PDT Fri Aug 29 2025

.KEY MESSAGES...

- Scattered showers with isolated thunderstorms in the northern
  mountains Friday. Thunderstorms will be capable of heavy
  rainfall.

- Warming up into the 90s next week, locally near 100, with
  elevated HeatRisk. Record warm temperatures for September
  possible.

&&

.SYNOPSIS...
The threat for showers and thunderstorms will shift into the
northern mountains today. Thunderstorms will bring the
potential for lightning and brief heavy rainfall. Isolated
showers and thunderstorms will be possible near the Cascade
crest over the weekend, otherwise the main story will be warming
and drying.  Hot temperatures return next week with highs
climbing back into the 90s to near 100 degrees.

&&

.DISCUSSION...
Friday through Sunday: The pesky upper low spinning over Western WA
on Thursday will begin to drift to the north today. In concert,
the axis of rich precipitable water will also drift northward
and the threat for showers and thunderstorms will migrate into
the northern mountains while midlevel drying works into southern
and portions of central WA. Highest thunderstorm probabilities
via the HREF extend from Bonners Ferry to Republic (40-60%) and
drop off toward 10-20% on the southern periphery from Couer D
Alene to the Methow Valley. Convection will largely be driven by
surface heating with weak lift associated with the drifting low
over the N Cascades and into the Okanogan Highlands.

By the weekend, a deeper low will take residence along the WA Coast.
This will allow a ridge to begin blossoming over the Inland NW
and start of a warming trend. The ridge axis will initially set
up near the Idaho/Montana border. Some moisture and weak
disturbances running up the western flank of the ridge will keep
a mention of showers and storms near to west of the Cascade
crest though the air mass will be considerably drier with less
instability leading to a higher threat for clouds and light
showers vs wet thunderstorms. Mean CAPES are forecast to be in
the 300-600 J/kg range with accompanying SREF probabilities for
lightning around 10%. As mentioned in the previous AFD, the
ridge and midlevel drying looks to be the more dominant feature
for much of the Inland NW for the upcoming weekend.

Monday through Friday: The deep low residing off the WA Coast
will retreat into the Gulf of AK and a strong ridge of high
pressure will amplify over the Northwest. Residents of the
Inland NW need to prepare for a multi-day heat wave with
temperatures surging into the 90s to lower 100s. This comes with
high confidence given strong support from the entire 100 member
ensemble output. The peak of the heatwave spans from Monday
through Wednesday but would not be surprised if Thursday and
Friday come in warmer in future model runs given the strength of
this ridge and only indicate 1-4 degrees of cooling compared to
Wednesday. Numerous deterministic models forecast 500mb heights
in excess of 5900 meters. Looking back at historical data for
500mb heights at the Spokane balloon data, the maximum height of
5996 meters was achieved on Sep 4, in 1988 and two other of the
top ten readings came in early September. So ridges in
September are not uncommon but heights in excess of 5900 meters
are and the NAEFS ensemble situational table indicates the
forecast heights of 5900 meters have a return interval of every
5 to 10 years in early September. /sb

&&

.AVIATION...
12Z TAFS: The area of low pressure responsible for showers and
thunderstorms near the Cascades on Thursday will drift northward
on Friday shifting the threat for convection into the northern
mountains. Bonners Ferry, Colville, Republic, and Omak have a
30-50% chance for lightning while Couer D Alene, Davenport, and
Winthrop vary from 10-20%. Confidence for activity to impact the
TAF sites is low. Modest drying in the midlevels will reduce
the threat for points further south. Thunderstorms will be
capable of torrential rainfall and scattered lightning.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence
in VFR conditions at most TAF sites. Low confidence for
thunderstorms impacting airport terminals with Omak, Colville,
and Bonners Ferry containing the highest potential. /sb

-----------------------

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        89  59  93  62  97  63 /   0   0   0   0   0   0
Coeur d`Alene  88  59  92  62  96  63 /  10  10   0   0   0   0
Pullman        87  54  92  59  94  58 /   0   0   0   0   0   0
Lewiston       94  65  97  66 100  67 /   0   0   0   0   0   0
Colville       89  49  92  51  94  52 /  20  10   0   0   0   0
Sandpoint      84  53  90  55  93  57 /  30  20   0   0   0   0
Kellogg        84  61  90  64  94  65 /  20  10   0   0   0   0
Moses Lake     92  58  94  64  97  63 /   0   0   0   0  10  10
Wenatchee      92  67  94  71  96  71 /   0   0   0  10  10  10
Omak           92  63  94  66  97  66 /  10  10   0   0   0  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
WA...None.
ID...Air Quality Alert until 10 AM PDT Tuesday for Lewis and
     Southern Nez Perce Counties-Lewiston Area.

&&

$$