Debris Flow in Washington, August 11, 2024

Area Forecast Discussion
National Weather Service Spokane WA
323 PM PDT Sun Aug 11 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...
This afternoon through Tuesday: The threat of showers and
thunderstorms will continue across some the Inland NW this
period. There are a lot of moving parts to this potential over the
next couple days or so. The main players will be a long-wave
trough near the west coast and the shortwaves embedded within it
and the instability these will interact with. This afternoon there
is a smattering of showers and isolated thunderstorms around the
periphery of the CWA. These have been mostly north of the Canadian
border, aside from a few stray cells over near the ID Panhandle
and near the northern mountain. However this activity is expected
to increase.

Toward the west and northern CWA: satellite showed a well-defined
circulation near northwest Washington around the 3 PM hour. As
this afternoon moves into tonight that circulation will gradually
move east. Instability and this feature is expected to lead to a
continued increased in showers and embedded thunderstorms around
the Cascades and northern mountains through this evening,
potentially spreading as far east of the Waterville Plateau or
northwest Columbia Basin. As the sun sets, the activity further
removed from the circulation center will wane. Closer to the
center around Okanogan county the threat of showers and t-storms
will continue through the night, though some models dissipate that
threat more than others. Activity dissipates here heading into
Monday morning, but will be revitalized here and the northern
mountains through the Monday afternoon. All of these are expected
to move a bit quicker and lessen the potential for wetting rains.
A Red Flag Warning remains in place for the Cascades to
north-central WA through Monday evening for lightning. Any
lightning that starts fires could could also be impacted by gusty
outflow winds from t-storms. The threat wanes through Monday night
only to return in more isolated fashion in the daytime heating
Tuesday afternoon.

Toward the southeast CWA, the upper trough pivoting in and the
aforementioned disturbances coming along it will also bring some
showers/t-storms chances in this area. Isolated activity is
possible this evening near the Blues and around the central
Panhandle mountains. A few could form around the Spokane/CdA area
and Palouse too, but there is very low confidence in that. As the
evening progresses into tonight the threat of showers will
persist over the Blues and also a higher confidence threat will
expand over the L-C Valley/Camas Prairie and Palouse to central
Panhandle as a shortwave pivots along the near jet axis. With all
that said, this activity is expected to be isolated in nature. The
chances will continue through Monday and then will be invigorated
late Monday into Tuesday morning in this same area as another
wave moves in along the jet. This will be slightly further north
than the first, meaning some potential may also slip a bit further
north into the Spokane/C'dA area late Monday night into Tuesday
morning. Heading into Tuesday afternoon the threat here starts to
shifts further east.

In a broader sense all of this will be accompanied by some marginally
breezy conditions, near the Cascades gaps and also on Monday and
Tuesday around the Columbia Basin and Palouse and lower Panhandle,
with gusts near 15-20 mph. Sustained winds and afternoon RHs are
not expected to reach critical values for fire weather concerns.
High temperatures are forecast to reach the upper 80s to low 90s
Monday and then the mid-70s to mid-80s on Tuesday. Overnight lows
will be in the upper 50s and 60s Monday morning and then the
upper 40s and 50s Tuesday morning and Wednesday morning, with
Wednesday morning the cooler of the two.

Wednesday to Sunday: The middle of the week starts cooler and dry
with weak high pressure, while a deeper trough starts to develop
around the coast heading into the end of the week. A leading wave
starts to move into the region Thursday night, expanding shower
and embedded t-storm chances across the region. There are still
model disagreements over the details heading into Friday through
Sunday, but they are coming together in developing a deeper trough
near the coast with waves moving inland. This bring continued and
broader shower/t-storm chances throughout the region in that time
frame. Overall the best chance for wetting rain will be around
the mountain zones at around 30-60%, with areas outside of the
mountains will have around 10-30%. Temperature warm closer to
normal on Thursday, then drop slightly below normal again Friday
into Sunday. Saturday looks like the coolest day with highs in
the mid-70s to low 80s, with some mid-80s in the L-C Valley.
/Solveig

&&

.AVIATION...
00Z TAFS: Low pressure dropping in from northwest will bring the
threat of showers/isolated t-storms around the Cascades and
northern mountains and northern and central ID Panhandle. The
threat over this region will wane after dark over all but
north-central WA, especially central and eastern Okanogan County
where the risk will continue through the night before waning into
early Monday AM. Elsewhere, later tonight into early Monday the
threat will develop around southeast WA and lower ID, potentially
moving into the areas such as PUW/LWS after 09-12Z. Wildfire
smoke will continue to bring hazy/smoky conditions, particularly
near the wildfires, but impacts at TAF sites are not expected at
this time. Otherwise look for VFR conditions. Winds will be
generally light, but if a t-storms passes near a TAF sites brief
gusty winds are possible.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high
for VFR conditions. General haziness from regional fires may
result in brief MVFR conditions with reduced visibility,
particularly in the Methow Valley and possibly at KPUW. Confidence
is high for thunderstorms near the Cascades this afternoon into
this evening, but confidence is low around TAF sites but the
threat is not zero.

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

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        62  87  56  81  53  83 /  10  10  10  10   0   0
Coeur d'Alene  60  85  54  80  52  80 /  20  10  10  20   0   0
Pullman        57  83  51  75  48  78 /  20  20  20  20   0   0
Lewiston       67  93  64  84  59  88 /  20  20  30  20   0   0
Colville       50  87  47  83  45  83 /  20  20  20  20  10   0
Sandpoint      57  84  52  79  50  79 /  20  10  10  10   0   0
Kellogg        64  83  57  77  55  78 /  30  20  20  20  10   0
Moses Lake     60  89  56  84  53  85 /   0  10   0   0   0   0
Wenatchee      66  89  62  84  61  85 /  20  10  10  10   0   0
Omak           63  92  61  88  58  90 /  30  30  20  20   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Red Flag Warning until 11 PM PDT Monday for East Portion of
     North Cascades National Park/Lake Chelan National
     Recreation Area (Zone 697)-East Washington Central Cascades
     (Zone 696)-East Washington North Cascades (Zone 698)-Methow
     Valley (Zone 704)-Okanogan Highlands and Kettle Mountains
     (Zone 699)-Okanogan Valley (Zone 703).

&&