075
FXUS66 KOTX 312327
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
427 PM PDT Fri May 31 2024

.SYNOPSIS...
A chance for light showers will return for the northern mountains
on Saturday, but most locations will remain dry. A dynamic system
pushes across the region late Sunday into Monday, bringing
widespread rain, followed by gusty winds, and the potential for
afternoon thunderstorms on Monday. Next week will see a warming
and drying trend. Confidence is increasing for temperatures
warming into the 80s and 90s.

&&

.DISCUSSION...
Tonight through Sunday: High pressure will start to move out,
opening the door for increasing precipitation chances for some as
we head into this weekend. Tonight the ridge axis will shift from
the Cascades to the northern Rockies. The afternoon cumulus build-
ups will start dissipate with sunset; however, higher clouds will
start to thicken from the west as the first shortwave system
approaches; then later overnight into early Saturday those clouds
will continue to thicken and lower. Tonight will be mostly dry,
save for some limited shower chances that approach the northern
Cascade crest toward daybreak.

Then Saturday the first shortwave system tracks over the region.
This relatively weak system will bring the best chance for
precipitation near the Cascades, Canadian border counties and the
ID Panhandle Mountain zones. However precipitation amounts look
relatively light. The exception: there could be locally heavier
downpours in the afternoon with any convectively enhanced showers
and isolated embedded t-storms, mainly over the northern mountains
and near the Camas Prairie. Elsewhere there is a limited risk for
showers extending from the Wenatchee area east across the Waterville
Plateau to the Spokane/CdA area and Palouse. However the potential
for measurable precipitation according to the ensembles is 10-20
percent, so what falls outside of the mountains maybe no more than
sprinkles. So the forecast leans toward that. Clouds decrease
overnight into Sunday morning, with the threat of showers
retreating further into the mountains and decreasing with brief
and weak ridging ahead of the next system. Winds will increase on
the backside of the trough later Saturday afternoon and evening,
especially near the Cascades and western basin with gusts of 15-25
mph. Temperatures are forecast to be near seasonal norms.

Heading into Sunday the next system starts to move into the
region, with the leading warm front starting to lift in through
the day and the parent upper trough/cold front moving toward the
Cascades later in the day. Clouds will thicken again through the
day, with precipitation chances increasing throughout the region
in the afternoon. How quickly that precipitation risk will
increase carries some disagreement. The NBM paints about a 20-30%
chance of measurable precipitation before 5PM Sunday (00Z Monday)
over the eastern third of WA and ID, with a 40-90% chance over
central WA to the Cascades (that higher range is in the Cascades).
The EC/GFS/CMC ensembles show that probability averaging around
45-50% over much of the area, with 70-90% chances in the Cascades.
I increased PoPs above the NBM, showing the higher risk remaining
in the Cascades and northern mountains and secondarily over
central and northeast WA and the lowest risk over southeast WA and
the lower ID Panhandle. However even then the precipitation
amounts away from the Cascades look relatively light, as the
heavier precipitation potential holds off until Sunday night into
Monday. Expect breezy conditions with wind gusts near 15-20 mph,
locally near 25-30 mph from the Okanogan Valley to the Upper
Columbia Basin. Temperatures are forecast to be slightly below
normal. /Solveig

Sunday night through Friday: An impactful period of weather is
expected with widespread moderate to heavy precipitation Sunday
night through Monday, breezy to gusty winds and thunderstorms Monday
afternoon, breezy winds and isolated thunderstorms Tuesday, and much
warmer temperatures possible Thursday through the weekend.

Sunday night through Monday: A strong shortwave and associated
frontal system will move toward the Pacific Northwest. Models are
in good agreement that this will be aided by a strong upper level
jet streak and a robust late-season atmospheric river. Precipitation
will spread east of the Cascades late Sunday afternoon within the
warm sector of the approaching system, then pick up overnight
Sunday into Monday morning as the stronger upper level dynamics
move east of the Cascades. By late Monday morning and the
afternoon, the focus will shift to widespread breezy to gusty
winds and potential for thunderstorms across eastern Washington
and north Idaho.

RAIN: Precipitation totals through Monday evening will be between 1
to 2 inches for the Cascade crest. East of the crest, strong
westerly flow will work against significant accumulations, but could
see between 0.05 to 0.25 inches with areas such as Moses Lake and
Wenatchee showing a 65-75% chance of 0.10 inches of rain from 5 PM
Sunday to 5 PM Monday. When increased to 0.25 inches this potential
decreases to 25-30% for the Moses Lake area and 40% for Wenatchee.
Areas further north such as Omak and the Methow Valley are showing a
60% chance for 0.25 inches. As the system moves into far eastern
Washington and north Idaho, precipitation amounts will re-enhance
with around a 60-70% chance for above 0.50 inches of rain for
Colville, Spokane, Pullman, and Lewiston. For 0.75 inches, this
potential decreases to 20-30%. Across the valleys of Idaho
Panhandle, there is nearly a 100% chance for over 0.50 inches,
including Coeur dAlene and Sandpoint. There is a 70% chance for
over 0.75 inches at these locations and a 35% chance for over an
inch.

WINDS: Expect winds to increase late Monday morning and peaking mid
afternoon and subsiding through Monday evening. Sustained winds of
20 to 30 mph with wind gusts of 35 to 45 mph are possible across the
lee of the Cascades through the Columbia Basin, and into the Spokane
area, the Palouse, and lower Asotin and Garfield counties. The best
chances to see wind gusts above 45 mph will be from the Waterville
Plateau and the upper Columbia Basin and the Blues with a 70-80
percent chance. Strong cross winds along highways will result in
difficult travel for high profile vehicles and rough water on area
lakes. Light weight objects could also be tossed around.

Tuesday through Friday: Another system will move across the region
late Monday into Tuesday, but will be much weaker. Right now this
looks to bring light precipitation across the Idaho Panhandle with
breezy winds.

By Wednesday, a strong ridge will amplify over the Western US as an
upper level low strengthens in the Gulf of Alaska. This will bring
an extended period of very warm temperatures to the Inland
Northwest, but there still remains a good amount of uncertainty on
how warm temperatures will get depending on the strength of the
ridge. Right now our forecast is showing widespread temperatures in
the mid 80s to low 90s by Friday. There are also a handful of
ensembles (about 30%) between the GEFS, ECMWF, and Canadian
ensembles showing the ridge beginning to shift eastward late
Thursday into Friday, allowing some elevated convection to move into
the Inland Northwest. The other 70% keep the ridge and very warm
temperatures in place through the weekend. /vmt


&&

.HYDROLOGY...
There is a Hydrologic Statement in effect focusing on rises to
stream, creeks, and some mainstem rivers. Base flows remain low
across the region, and a good portion of the Inland Northwest is
within a moderate drought (including the Cascades) and even a severe
drought in the central portion of the Panhandle. Due to the ongoing
drought conditions, the rain that is expected will largely be
beneficial. With that said, the amount of water with a little bit of
snow left to be melted on the highest elevations of the Cascades
will result in a steep rise on the Stehekin River. Flooding is not
anticipated at this time but will need to be monitored. Another
potential impact will be for rock slides on steeper slopes in the
Cascades and across the Idaho Panhandle.


&&

.AVIATION...
00Z TAFS: VFR conditions with generally light winds expected for
TAF sites over the next 24 hours. A shortwave system moves in
later tonight into early Saturday, increasing upper level clouds
this evening, then lowering and thickening clouds overnight into
Saturday morning. Sites remaining VFR, but mountain obscuration
near Cascades and north-central WA. Shower chances move into the
Cascades and north-central WA mountains Saturday morning.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
High confidence in VFR conditions at TAF sites. Low confidence
(less than 15%) for -shra in EAT, MWH, GEG Saturday morning with
incoming wave.

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

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        47  72  47  67  51  63 /   0  10   0  30 100  90
Coeur d`Alene  46  69  47  64  51  60 /   0  10  10  20 100 100
Pullman        45  70  47  66  51  60 /   0  10   0  20  90 100
Lewiston       51  79  54  72  58  70 /   0  10   0  10  90 100
Colville       42  69  42  66  45  63 /   0  30  20  40 100 100
Sandpoint      44  66  46  62  50  57 /   0  10  20  30 100 100
Kellogg        47  67  50  64  53  56 /   0  10  10  30 100 100
Moses Lake     52  78  48  70  52  70 /   0  10   0  30  80  50
Wenatchee      57  74  51  67  54  65 /   0  10   0  40  80  60
Omak           52  76  47  67  50  70 /   0  20   0  30  80  70

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$