480
FXUS66 KOTX 311148
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
448 AM PDT Fri May 31 2024

.SYNOPSIS...
Dry and warmer weather is expected for today. A chance for light
showers will return for the northern mountains on Saturday, but
most locations will remain dry. A dynamic storm system will push
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, and confidence is increasing for temperatures warming into
the 80s and 90s.

&&

.DISCUSSION...

...DYNAMIC SPRING STORM SUNDAY NIGHT INTO MONDAY TO BRING WIDESPREAD
RAIN FOLLOWED BY GUSTY WINDS AND A POTENTIAL FOR THUNDERSTORMS...

Today through Sunday: A shortwave ridge will be in place across
the Inland Northwest today. After a chilly morning, dry and warmer
conditions are anticipated for the afternoon. A weak wave on
Saturday may bring light showers to the higher terrain of northern
WA. In addition, breezy winds will develop across the Cascade Gaps
and into the western Columbia Basin Saturday afternoon and evening.
Sunday will be a transitional period in advance of an approaching
storm system, but most locations should remain dry through at
least the morning hours. /KD

Sunday night through Monday night: A spring storm system is on track
to produce minor to moderate impacts across the Inland Northwest on
Monday. There are three variables of note that will be monitored as
this storm system approaches: (1) rain, (2) wind, (3) thunderstorms.
A strong 150+ kt jet streak will be directed into the Northwest.
It`s late in the season for such a dynamic Polar Jet to develop. The
strength of this jet on the backside of the upper level trough will
act to give it a slight negative tilt as it pushes across the Inland
Northwest on Monday. It will also bring with it a moderate strong
Atmospheric River (AR 3 level event) that will be focused more so
across the state of Oregon, but a good portion of the moisture will
penetrate across eastern Washington and into the Idaho Panhandle.
The warm front will move in late on Sunday. It will take a little
bit of time to moisten the atmosphere from the top down to the
surface, but won`t take too long with the firehose of moisture being
directed into the region. Widespread stratiform rain will be upon
the region by Sunday evening. This is slightly faster than
previously forecast. Strong westerly flow across the Cascades will
keep rainfall amounts down in the lee of the Cascades with the focus
of heavier rainfall along the Cascade crest and in the favorable
upslope areas of the Idaho Panhandle (see rainfall section for
amounts and probabilistic guidance).

The next potential for widespread impacts will be from the winds
that pick up as the rain shuts off, or becomes convective late in
the morning into the afternoon and evening. Impacts from winds look
to be overall minor as at 850 mbs models are only indicating up to
around 35 kts. The pressure gradient will become tight and we will
see a moderately strong synoptically driven wind, but gust potential
could be limited by the lack of stronger winds aloft as the upper
level jet dips south of the region. The caveat to wind gust
potential will be with any convection that develops. Ensembles are
indicating the potential for 200-400 J/kg of surface based CAPE.
This doesn`t sound like a lot, but any thunderstorms that develop
will be capable of enhancing wind gusts from the 35-40 mph magnitude
closer to 50 mph. The breadth and magnitude of convection are finer
details that will continue to be worked out as the event nears. What
I can say with high confidence is that we will see rain across much
of the region. Westerly winds will increase and become gusty Monday
afternoon. The dynamics accompanying the upper level trough will be
moderate to strong and should be enough to overcome deficiencies in
instability. Convection may develop in the short window as the
stratiform rain ends just out ahead of the vorticity maximum
pivoting around the upper level trough. There will be plenty of bulk
shear for convection to become organized if ingredients all line up.

* Rain Amounts: This is the part of the forecast where confidence is
  highest. In general, the Cascade crest is looking at storm total
  rainfall of between 1.25-2.5 inches south of Lake Chelan and
  between 0.50-1.25 north of Lake Chelan. Places such as Omak,
  Wenatchee, and Moses Lake may have a difficult time getting a
  tenth of an inch due to downsloping effects off of the Cascades.
  Rainfall amounts will then precipitously increas over extreme
  eastern Washington and in the Idaho Panhandle with around 0.5-1.0
  inches expected for Colville, Spokane, Pullman, and Lewiston. Then
  between 1.0-2.0 inches expected in the Idaho Panhandle with the
  westerly slopes of the higher terrain likely wringing out the most
  moisture. A near certainty that the Cascade crest will see at
  least an inch and around an 80% chance for at least 1.5 inches.
  The Idaho Panhandle has a 30-60% chance for at least an inch and
  around a 10% chance for more than 1.5 inches.

* Winds: Expect widespread sustained winds of 20-25 mph with gusts
  of up to 35-40 mph across the exposed areas of the basin. This
  will includes in the lee of the Cascades across the Wenatchee
  Area, into the Moses Lake Area, Spokane Area, Palouse, and lower
  Asotin and Garfield County. These winds look to be sub-advisory
  criteria; although, there will be spots that will be flirting with
  45 mph wind gusts -- namely Spokane West Plains, Palouse, and
  lower Garfield/Asotin County.

* Thunderstorms: Lowest confidence for this potential. Timing and
  strength of the vorticity maximum that pivots across will be
  crucial on the strength of thunderstorms that we see. Areas that
  will see the best chances will be across extreme eastern
  Washington and the Idaho Panhandle at 15-30% chances.

* Impacts: Best potential for moderate impacts will be with any
  thunderstorms that develop because they will be capable of
  becoming organized and would enhance the potential for wind gusts
  at the surface. It`s possible that in this scenario that we would
  see 50+ mph wind gusts, but this carries low confidence.
  Ingredients would all have to come together. Otherwise, we are
  mainly looking at minor impacts from rain (see hydrology section
  below) and wind. Strong cross winds ware expected making travel
  difficult for high profile vehicles and light weight objects may
  become airborne.

Tuesday through Friday: Another warm front pushes across Monday
night into Tuesday. Isentropic ascent will be favorable for light
precipitation, but upper level dynamics will be lacking with this
secondary shortwave. More in the way of increased cloud cover and
light precipitation, but not expecting additional impacts with
this. Then a strong ridge of high pressure begins to build in for
the remainder of the week. The question remains how strong will the
ridge become and how hot as we go into the following weekend. There
is high confidence for warm weather, and the heat risk will be on
the rise. Where uncertainty remains is if the heat will rise to the
level of causing widespread heat related illness type impacts.
Expect additional messaging on the potential for heat as we move
through next week. /SVH

&&

.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. /SVH

&&

.AVIATION...
12Z TAFS: VFR conditions with generally light winds expected for
TAF sites over the next 24 hours. Increasing upper level
cloudiness anticipated Friday evening.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Confidence is high for VFR conditions for TAF sites. /KD

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

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        70  47  72  48  68  53 /   0   0   0   0  10 100
Coeur d`Alene  69  46  69  47  67  52 /   0   0   0  10  10 100
Pullman        67  46  69  47  66  52 /   0   0   0   0  10 100
Lewiston       76  51  78  54  75  59 /   0   0   0   0  10  90
Colville       71  41  68  42  67  45 /   0   0  20  20  30 100
Sandpoint      67  44  66  46  65  51 /   0   0  10  20  20 100
Kellogg        66  46  68  51  65  54 /   0   0  10  20  10 100
Moses Lake     76  50  78  48  70  53 /   0   0   0   0  20  80
Wenatchee      76  57  74  52  68  55 /   0   0   0   0  30  80
Omak           76  51  75  47  69  51 /   0   0  10   0  20  90

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Frost Advisory until 8 AM PDT this morning for Central Panhandle
     Mountains-Idaho Palouse-Northern Panhandle.

WA...Frost Advisory until 8 AM PDT this morning for Spokane Area-
     Upper Columbia Basin-Washington Palouse-Western Okanogan
     County.

     Freeze Warning until 8 AM PDT this morning for Northeast
     Mountains-Okanogan Highlands.

&&

$$