454
FXUS66 KOTX 121801
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1101 AM PDT Mon Aug 12 2024

.SYNOPSIS...
There will be a couple more days of showers and thunderstorms for
some of the region, followed by a brief lull around mid-week,
before additional shower and thunderstorm chances arrive heading
into the end of the week. In the near term, the focus for
thunderstorms will be over the Cascade and northern mountains, as
well as over southeastern Washington into the southern Panhandle
tonight through Monday night. Lightning from thunderstorms will be
capable of starting new fires. Daytime temperatures will begin
the week slightly warmer than normal but should drop to average or
slightly below by midweek.

&&

DISCUSSION...

Today through Tuesday night: A compact upper level low is swinging
across north-central Washington early this morning. A vorticity
maximum moving across the northern Cascades is interacting with
between 200-300 J/kg of MUCAPE to force thunderstorms in the area.
These storms are slow moving to the north and contain brief heavy
rain, small hail, along with frequent lightning. The prognoses is
for this low to slowly track into the Okanogan Highlands this
afternoon. Model guidance suggests between 500-800 J/kg of surface
based CAPE to work with in the Cascades over to the Okanogan
Highlands, Northeast Mountains and Idaho Panhandle. Thunderstorms
are expected to expand in coverage as lower levels destabilize this
afternoon under the cold pool. Steering flow will be weak and P-wats
on the order of 0.9+ inches. Concerns with thunderstorms today will
be two fold: flooding/debris flows near burn scars and new fire
starts from lightning strikes. Good news is that rain from
thunderstorms will act to extinguish new fire starts. Will maintain
the red flag warning over the Cascades to the Okanogan Highlands.

There is also some mid level instability to contend with across
southeast Washington into the Central Panhandle Mountains.
Instability is fairly weak with out much in the way of dynamics to
get convection going. I expect that these areas will mainly just see
ACCAS and virga this morning. A better chance for nocturnal
convection will come Monday night into Tuesday morning over
southeast Washington into the southern and central Idaho Panhandle.
The NAM is suggesting better MUCAPEs on the order of up to 400-500
J/kg and a shortwave disturbance pushing northeast out of northern
California and southern Oregon. I went ahead and maintained a 15-30%
chance for higher based thunderstorms. These storms will be moving
fast, thus be drier and may be a higher threat for lightning caused
fires.

Winds will be generally breezy through the Cascade gaps and out over
the basin sustained at 10-15 mph and gusts up to around 25 mph.
Winds will increase this afternoon and remain breezy through Monday
night into Tuesday. Temperatures will cool to near normal by Tuesday
with highs in the upper 70s to the mid 80s. /SVH

Wednesday through Sunday: Weak high pressure of the mid part of the
week becomes altered as a large upper area of low pressure
intensifies and digs southward off the coast toward the end of the
week and remains more or less in the same area over the weekend. The
end result will be a warming trend peaking on Thursday. Benign
conditions under weak high pressure Wednesday give way to a warm
southwesterly flow increasing moisture and instability and allowing
for a more unsettled Thursday evening and beyond. Pops for showers
and thunderstorms and a bit more cloud cover is likely to result in
slightly cooler temperatures after they peak Thursday and more or
less continue on as such through the weekend as the offshore upper
area of low pressure remains in place and allows for continued
moisture, instability, and small trigger disturbances to be steered
overhead in a southwest to northeast or south to north trajectory
across Eastern Washington and North Idaho. /Pelatti

&&

.AVIATION...
18Z TAFS: A compact upper level low pressure system will track
from the Cascades into northeast Washington today. Widely
scattered thunderstorms are expected near airports from the Methow
Valley (KS52), Omak (KOMK), Colville (KCQV), and Bonners Ferry
(K65S). An axis of mid level instability across southeast
Washington to the Central Panhandle Mountains will result in mid
to level clouds, including ACCAS cover, but mainly only expecting
isolated showers. Westerly winds will increase through the
Cascades late this afternoon with gusts of 15-20 kts at KEAT
expected into the evening. Nocturnal thunderstorms are expected to
push northeast out of northeast Oregon Monday night into Tuesday
morning. These storms may impact the Pullman/Moscow (KPUW) and
Lewiston (KLWS) airports after 06Z.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high
for VFR conditions. High confidence for thunderstorms over the
Cascades and northern mountains today. Low confidence for
thunderstorms elsewhere across the region, including nocturnal
thunderstorms Monday night into Tuesday morning in the vicinity of
KPUW and KLWS.

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

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        88  56  80  53  83  56 /   0  10  10   0   0   0
Coeur d`Alene  86  55  79  52  81  54 /  20  10  20   0   0   0
Pullman        83  52  75  47  79  51 /  20  20  20   0   0   0
Lewiston       93  63  85  60  88  61 /  20  20  40   0   0   0
Colville       87  47  83  45  83  46 /  20  20  10   0   0   0
Sandpoint      83  52  79  50  80  51 /  20  10  10   0   0   0
Kellogg        83  57  76  54  79  58 /  20  20  20  10   0   0
Moses Lake     89  56  84  53  85  55 /   0   0   0   0   0   0
Wenatchee      88  62  85  61  86  64 /  10  10  10   0   0   0
Omak           92  61  89  59  90  60 /  30  20  10  10   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Flood Watch through this evening for Okanogan Highlands-Okanogan
     Valley-Upper Columbia Basin-Western Okanogan County.

     Red Flag Warning until 8 PM PDT this evening for East Washington
     North Cascades (Zone 698)-Methow Valley (Zone 704)-Okanogan
     Highlands and Kettle Mountains (Zone 699)-Okanogan Valley
     (Zone 703).

     Red Flag Warning until noon PDT today for East Portion of North
     Cascades National Park/Lake Chelan National Recreation Area
     (Zone 697)-East Washington Central Cascades (Zone 696).

&&

$$