034
FXUS66 KOTX 021210
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
510 AM PDT Sun Jun 2 2024

.SYNOPSIS...
A vigorous storm will make its entrance today bringing widespread
rain through Monday, and windy conditions for Monday afternoon.
There will also be a chance for thunderstorms late Monday morning
into Monday afternoon. Next week will see a significant warming
and drying trend. Confidence is increasing for temperatures
warming into the 80s and 90s.

&&

.DISCUSSION...

...DYNAMIC SPRING STORM TO BRING WIDESPREAD RAIN SUNDAY INTO MONDAY
FOLLOWED BY A CHANCE FOR THUNDERSTORMS AND WINDY CONDITIONS...

Today through Monday night: Satellite imagery early this morning
shows a vigorous storm system making its way toward the Northwest.
A strong jet streak of 160-170 mph will fuel a surface low that
will track toward Vancouver Island today, across southern BC
tonight, and then into southern Alberta on Monday. With the upper
level jet will be a moderately strong Atmospheric River (AR 2
level event) that will focus moderate to heavy precipitation along
the Cascade crest and over the Idaho Panhandle. Widespread
stratiform rain will be upon the region by Sunday afternoon with
heaviest amounts falling Sunday night into early Monday. The
trailing cold front will move into the Cascades Monday morning and
into the Idaho Panhandle by mid afternoon friday. The cold front
will bring strong dynamical forcing that will be supported by
strong dynamics aloft: bot with a strong vorticity maximum at the
base of the upper level trough and within the left exit region of
the upper level jet.

Lapse rates will steepen at lower to mid level of the atmosphere.
Rain will moisten the boundary layer with a -22 Celsius cold pool
aloft with the upper level trough also advancing in over the region.
lower levels will destabilize right ahead of the surface front with
favorable conditions for at least low topped convection to form.
Model guidance shows the potential for 200-500 J/kg of surface based
CAPE, which will be enough for thunderstorms to form as strong
dynamics will compensate for only modest amounts of instability. A
tight pressure gradient will also result in windy conditions and
these winds may be enhanced by any developing convection. Cold air
advection will also result in lowering snow levels over the Cascades
with slop over precipitation changing over to snow over the higher
mountains above 4,500 to 5,000 feet. This will be low enough for
snow to fall over Washington Pass in the north Cascades with 2 to 4
inches of accumulation expected.

* Rain Amounts: Not much has changed with the precipitation
  forecast. In general, the Cascade crest is looking at storm total
  rainfall of between 2.0-3.25 inches south of Lake Chelan and
  between 1.25-2.0 inches north of Lake Chelan (with a transition to
  snow above 4,500 feet). Places such as Omak, Wenatchee, and Moses
  Lake will see downsloping off the Cascades with much less in the
  way of total accumulations in the range of 0.05-0.20 inches.
  Rainfall amounts will then precipitously increase 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 1.25-2.25 inches expected in the Idaho Panhandle with the
  westerly slopes of the higher terrain likely wringing out the most
  moisture. Probability of at least an inch in the Idaho Panhandle
  varies wildly as there will be a strong orographic component. The
  Silver Valley, Bonners Ferry, Lewiston-Clarkston Valley, and
  western portions of the Camas Prairie will see a fair amount of
  downsloping off of the higher terrain. A near certainty for at
  least an inch for the higher terrain especially westerly and
  southerly slopes, including the Cascade crest. Probabilities fall
  to 50-60% for getting at least 2 inches of precipitation; although
  the Cascade crest will see at least a 70% chance for 2 inches of
  precipitation.

* Winds: Trended winds a little bit stronger for Monday afternoon
  over the southeast portion of the forecast area. Winds across the
  foothills of the Blue Mountains will be flirting with high winds,
  sustained at 30-40 mph and gusts up to 55 mph possible. Confidence
  isn`t high enough to go with a High Wind Warning. Strong winds
  look to downslope off of the Northeast Blue Mountains onto the
  Palouse. Locations such as Pomeroy, Uniontown, and Pullman/Moscow
  will see the potential for 50+ mph wind gusts. Winds in the lee of
  the Cascades and across the basin into the Spokane/Coeur d`Alene
  area will see the potential for 25-30 mph winds with gusts of 45-
  50 mph. Strongest winds are expected with the cold front passage
  in the afternoon. A Wind Advisory is in effect starting late
  Monday morning through Monday evening.

* Thunderstorms: As previously mentioned, the potential for
  thunderstorms will be greatest with the surface front from late
  morning into the afternoon hours on Monday. This will be the
  period of the best combination of moisture, instability, and
  forcing -- the three ingredients need for convection. Instability
  will be a limiting factor, but the combination of dynamics along
  the cold front and aloft should be enough to overcome this
  deficiency. Convective Allowing Models (CAMs) show the bes
  potential for thunderstorms developing from the Moses Lake Area to
  the Central Panhandle Mountains and points northward. This is
  where the best instability will be as the front pushes through.
  The probability for thunderstorms is between 15-30%. The Palouse
  to the Camas Prairie will see a 10-20% chance for thunderstorms as
  well. Unidirectional bulk shear of around 40 kts may result in
  convection becoming organized in a linear fashion that would
  increase the potential enhanced wind gusts.

* Impacts: Moderate impacts from winds are expected regionwide.
  Synoptically driven winds will result in strong cross winds,
  especially for high profile vehicles. Major highways such as
  I-90, US-2, US-95, US-195, and US-12 will be routes that could
  see strong cross winds on Monday. Tree damage and scattered
  power outages will be likely. Winds may be strong enough to
  topple trees, but these impacts are expected to be isolated in
  nature, The caveat is if thunderstorms do organize because it
  won`t take much for strong convection to mix down damaging wind
  gusts on a broader scale. Rain over the Cascade crest and in the
  Idaho Panhandle may result in minor flooding impacts well. /SVH

Tuesday...Ensemble model guidance is in very good agreement that the
Inland NW will be under zonal flow with a 125kt westerly jet
lifting into southern BC during the day. The jet is also expected
to push another weak atmospheric river at least across the
southern portions of WA into the southern half of the ID
Panhandle. The amount of precipitable water will pale compared to
the system today-Monday, however it will assuredly bring another
round of precipitation but it shouldnt be heavy due to a stronger
rain-shadow effect in the lee of the Cascades and significantly
weaker atmospheric dynamics. Rainfall amounts will generally be a
tenth of an inch or less with close to nothing across the western
Columbia Basin. Deep instability will also be lacking with the
upper level cold pool fixed well north of the Canadian border so
we arent expecting thunderstorms at this point. It will also
remain breezy on Tuesday, however nothing like the speeds forecast
for Monday. We should see wind gusts of 30-35 mph in the
afternoon across portions of central Washington.

Wednesday-Friday...There is very good ensemble agreement that a
strong ridge will develop by midweek over the entire Western US
in response to a deep trough forming between 140-150w. The result
will be a significant warming and drying trend. 850 mb
temperatures will climb from the 7-12C range on Tuesday to the
19-22C range on Friday. This translates to highs warming from the
60s to lower 70s on Tuesday to the 80s and potentially the lower
90s on Friday. However by Friday there are some significant model
differences in the placement of the ridge axis. The Euro ensembles
place it over the Cascades as do the Canadian runs, however the
GEFS runs push the axis into western Montana with the
aforementioned trough nearing the coast. The offshoot of these
differences will be subtle in terms of temperatures, however it
will influence whether or not we see precipitation develop in
response to some ejecting energy riding NE off the offshore
trough. The GEFS solutions continue to suggest this will spark
some precipitation both Thursday and Friday afternoon, most likely
in the form of thunderstorms. If we look at this from a cluster
perspective (rather than ensemble specific perspective), the odds
look a little greater with nearly 30% of the runs showing some
precipitation in this area Thursday afternoon and evening and a
little lesser chance Friday afternoon and evening. Suffice it to
say confidence is too low to place in the forecast grids for now,
but this will need to be monitored.

Saturday and Sunday...For the weekend weather the model confidence
continues to decrease. Each ensemble package is different.
Although they all show a strong ridge over the region, the
placement of the axis is vastly different. The EC pushes it into
eastern Washington with the GEFS and Canadian solutions move it
into central or western MT with the trough moving onto the coast.
The Canadian runs have changed significantly over the past 24
hours while the Euro runs have remained persistent. The closer the
trough is to the Inland NW, the wetter and cooler the forecast
will be. It still looks like Saturday will be the hottest day of
the week with high temperatures ranging from the mid 80s to mid
90s. And it could be even hotter than that over portions of
central Washington. There is a 20-30% chance of seeing triple
digit heat for Wenatchee, Moses Lake, Omak, and Othello. There
will also be a small chance in the LC valley. By Sunday all the
solutions either flatten the ridge or move it farther east of our
region. This should bring cooling temperatures, but to what extent
is questionable. If the Canadian solutions verify wed cool off
by at least 10F, but this scenario only represents only 15% of the
total ensemble solutions, so we arent sold. A tougher question
is will we see precipitation? Certainly we would if the more
aggressive Canadian solutions wins out, however the other 85% of
the runs show little if any precipitation right now. fx

&&

.HYDROLOGY...
An Areal Flood Watch remains in effect for Lewis and Shoshone
Counties in Idaho. There will be an enhanced potential for increases
on small streams and creeks for these areas. For the rest of the
forecast area, rain will be largely beneficial due to antecedent dry
soils and low base river flows. Flooding is not anticipated at this
time on larger rivers 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: A wet Pacific storm system will move in over the Inland
Northwest today bring widepsread rain and deteriorating conditions
to all airports. Rain will move into KOMK-KEAT-KEPH-KMWH between
18-20Z and then into KCQV-KSZT-KGEG-KSFF-KCOE-KPUW-KLWS between
20-23Z this afternoon. Expect MVFR conditions as the boundary
layer moistens up with the rain. Winds will increase a bit with
gusts up to 15-24 kt ahead of the incoming rain. Moderate rainfall
with visibility down to 2SM is expected for extreme eastern
Washington and the Idaho Panhandle later in the afternoon after
00Z resulting in periods of IFR conditions.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence
in moderate rainfall 00Z Monday-06Z Tuesday resulting MVFR
conditions. Confidence is moderate for IFR conditions with a
40-60% chance for visibility down to 2SM during this same period.
Rain may let up and become light between 06-12Z Saturday night
with the potential for the potential of ceilings lifting above 3
kft and VFR conditions. /SVH

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

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        66  50  62  43  66  44 /  70 100  90  10  30   0
Coeur d`Alene  64  50  59  42  60  46 /  70 100 100  20  40  10
Pullman        64  50  58  42  62  46 /  70 100 100  20  30  10
Lewiston       72  57  69  50  71  54 /  60 100 100  10  20   0
Colville       66  44  62  35  62  36 /  80 100 100  20  40  10
Sandpoint      62  49  57  40  56  43 /  70 100 100  50  60  40
Kellogg        62  51  55  44  57  48 /  70 100 100  50  50  30
Moses Lake     68  51  67  47  74  44 /  80  80  50  10  10   0
Wenatchee      66  54  63  49  68  47 /  80  80  50  10  30   0
Omak           68  49  68  43  70  42 /  80  90  60  10  20   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory from 8 AM to 11 PM PDT Monday for Central
     Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse-Lewis
     and Southern Nez Perce Counties-Lewiston Area.

     Flood Watch from this afternoon through Monday evening for
     Central Panhandle Mountains-Lewis and Southern Nez Perce
     Counties.

WA...Wind Advisory from 8 AM to 11 PM PDT Monday for Lower Garfield
     and Asotin Counties-Moses Lake Area-Spokane Area-Upper
     Columbia Basin-Washington Palouse-Waterville Plateau-
     Wenatchee Area.

&&

$$