714
FXUS66 KOTX 031018
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
318 AM PDT Wed Jul 3 2024

.SYNOPSIS...
Mountain showers, seasonal temperatures, and breezy winds will
recur through Wednesday. Confidence is increasing in a substantial
long duration heatwave starting after July 4th. It is expected to
last through midweek.

&&

.DISCUSSION...

Today through Thursday: High pressure is strengthening off the Western US
coastline placing the Inland NW under persistent northwest flow aloft.
A 80-90kt jet will be in place through Wednesday night with the jet
migrating slowly to the north/northeast. This will keep a small
threat for weaker disturbances to slide through far NE WA and N ID
but nothing as organized as late Tuesday night where clusters of
storms tracked between Colville-Deer Park-Sandpoint- Prichard.
This convective activity was also being escorted by 4 Celsius of
cooling at 500mb which cooled from near -15C to -18C overnight.
Today, the pendulum will begin to swing the opposite direction
warming from -18C this morning to -16C in the afternoon.
Consequently, showers and storms will redevelop over far NE WA and
N ID around midday (with greater expansion southward into the
Silver and St Joe Valleys) however cloud depths will shrink with
time given the subtle warming aloft and most CAM models are
showing just a few cells lingering after 6PM along the ID-MT
border. One of the outlying CAMS does show a few cells in the
Upper Columbia Basin but this comes with very low confidence.
CAPES this afternoon will be several magnitudes lower topping out
between 200-400 J/kg for the aforementioned areas. For much of
Central and Southeastern WA, it will be another warm and dry day
with temperatures in the 80s. Winds will not be as strong as
Tuesday but still on the breezy side with gusts up to 20 mph. Wind
direction will be from the west and northwest. The Cascade Gaps
should anticipate another push of winds enhanced in the early
evening from the west and northwest with gusts up to 30 mph.
Overall, the HREF is showing far less coverage for joint
probabilities of winds greater than 15 mph and humidity levels
between 20%.

On Thursday, the offshore ridge will begin to expand inland.
Temperatures continue to warm aloft and any threat for showers or
weak t-storms will migrate toward Bonners Ferry and points north
and east. Therefore, the majority of the Inland NW will be under
stable weather conditions with temperatures warming a handful of
degrees, topping out in the 80s to lower 90s. Winds will weaken
with speeds largely below 10 mph. The evening will feature mostly
clear skies, light winds, and temperatures ranging from the
50-70s. The benign weather conditions will make for a gorgeous
evening to celebrate with friends and family for 4th of July
festivities. /sb

Friday through Wednesday: Clusters are in excellent agreement for
the onset of the heatwave beginning late this week into the weekend.
The ridge axis Friday is progged off the coast of western
Washington. Temperatures Friday peak will in the upper 80s to upper
90s. There is some potential for pockets of 100 degree high
temperatures Friday (Wenatchee: 55%, Moses Lake: 25%, Lewiston:
75%). By Saturday the cluster guidance shows a deepening ridge still
off the Washington coast. High temperatures will be in the low 90s
to low 100s Saturday.

By Sunday, 80% of the clusters move the ridge axis into at least
Western Washington with a small portion of them (15%) showing the
axis centered over central Washington. Temperatures Sunday will be
in the mid 90s to mid 100s. If the ridge axis is centered over
central or eastern Washington by Sunday like 15% of the ensemble
shows, we could push upper 90s to upper 100s. The remaining 20% of
the clusters still have the ridge offshore Sunday. An offshore ridge
Sunday would yield temperatures in the low 90s to low 100s similar
to Saturday.

70% of the clusters bring the ridge axis over central Washington to
northern Idaho by Monday/Tuesday which would maximize our HeatRisk.
Temperatures would be widespread 100 degrees or more (expect for
Idaho). Parts of the L-C valley have a 30-60% chance of 110 degrees
or more Monday/Tuesday. There is an even 50-50 split headed into
Wednesday and beyond with the position of the ridge over central
Montana or still over us. The ridge axis still over us Wednesday
would yield the temperatures similar to Monday/Tuesday. Butler

&&

.AVIATION...
06Z TAFS: Scattered showers and isolated t-storms will dissipate
in coverage after dark over NE WA and N ID. Some lingering
showers may drift south by the Spokane to Coeur d`Alene area, but
for the most part it is expected to be dry at TAF sites. Gusty
winds will abate. However some localized LLWS is possible,
including near MWH and PUW. Some patchy fog is possible in the
sheltered northeast valleys later overnight/early Wednesday from
the rain showers. TAF sites are projected to be VFR.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in
VFR conditions. Lows confidence in dying showers slipping south by
GEG, SFF, COE late this evening/overnight.

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

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:/www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        83  54  87  58  92  62 /  10   0   0   0   0   0
Coeur d`Alene  79  53  84  57  88  61 /  10   0   0   0   0   0
Pullman        78  52  84  54  89  57 /   0   0   0   0   0   0
Lewiston       87  60  93  64  98  67 /   0   0   0   0   0   0
Colville       81  47  85  50  90  54 /  10   0   0   0   0   0
Sandpoint      76  49  81  52  85  55 /  20  10   0   0   0   0
Kellogg        74  56  79  59  84  61 /  20   0   0   0   0   0
Moses Lake     88  55  93  61  99  64 /   0   0   0   0   0   0
Wenatchee      88  60  92  65  99  68 /   0   0   0   0   0   0
Omak           88  57  93  61  99  64 /   0   0   0   0   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Excessive Heat Warning from noon Saturday to 10 PM PDT Tuesday
     for Coeur d`Alene Area-Idaho Palouse-Lewis and Southern Nez
     Perce Counties-Lewiston Area.

WA...Excessive Heat Warning from noon Saturday to 10 PM PDT Tuesday
     for Central Chelan County-Lower Garfield and Asotin
     Counties-Moses Lake Area-Northeast Blue Mountains-Okanogan
     Valley-Spokane Area-Upper Columbia Basin-Washington Palouse-
     Waterville Plateau-Wenatchee Area-Western Okanogan County.

&&

$$