833
FXUS66 KOTX 022257
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
357 PM 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...

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

Tonight through Tuesday night:  It will be active 48 hours of weather
as a strong Pacific jet slams into the PacNW delivering strong
winds, moderate to heavy precipitation, and chance for
thunderstorms. A trough of low pressure on the nose of the jet is
beginning to swing inland today and with that, ushering a late
season atmospheric river. For the next 12 hours, the main weather
impacts will be steady light to moderate rainfall. This will be
accompanied by breezy southerly winds with gusts near 25 mph yet
these winds will pose little to no impacts.

The concern for weather impacts arrives Monday morning and continues
into the early evening. As the trough swings inland, rapid
cooling aloft will steepen lapse rates and transition steady
stratiform precipitation toward convective showers and
thunderstorms. Convective showers/t-storms will initially develop
along the surface cold front as it crosses west to east between
9AM - 2PM. Once this front clears east of Idaho, convection will
become more widely scattered in nature and continue on and off
through the early evening across Northeastern WA, North Idaho, and
along the Cascade Crest. Meanwhile, a deepening low across
southern Alberta-Saskatchewan will ramp up pressure gradients
across the region promoting windy conditions. The general
magnitude of the pressure gradient will be on the order of 14-18
millibars, adequate to support wind advisory strength wind speeds
(sustained 20-30 mph w/ gusts around 40-50 mph). The concern for
stronger winds comes in the proximity of the convection
(showers/t-storms) where downdrafts could tap into stronger winds
aloft and briefly drive them to the surface. These would be closer
to the 50-60 mph range. The threat for these winds will be more
isolated and localized. Given the best chance for convection, the
focus for these stronger downdraft winds will be in the central
and eastern Columbia Basin, Palouse, Spokane-Cd`A Area, and into
North Idaho and Northeastern WA. Wind advisories were expanded
into NE WA and N ID to address the potential for these winds.

Two other areas that could experience similar winds but for reasons
outside convection include the foothills of the Blue Mountains
and into the Palouse where several hi-res models are showing
strong enough synoptic wind speeds to come close to gusts near or
above 50 mph. This includes locations like Pomeroy, Peola,
Uniontown, Colton, and Moscow-Pullman. The second area is in the
lee of the Cascades in the foothills around Wenatchee and on the
Waterville Plateau. Similar hi-res modeling indicates a second
burst of stronger speeds near sundown with gusts on the higher
benches nearing 50-55 mph. This comes as the northwest jet aloft
is lifting northward over the Cascades and aligning with the
terrain and will need to monitored in the afternoon.

So overall impacts across the Inland Northwest will be most notable
from the winds. Tree damage and power outages will be a concern.
Those traveling in high profile vehicles should be wearing of
strong cross winds and keep cognizant near any showers or
thunderstorms for bursts of stronger winds. Lakes will be
challenging to navigate, especially for smaller vessels and
kayaks.

As for precipitation amounts and impacts.  Current thinking continues
to support the idea that this will be mainly be a beneficial rain
for the Inland Northwest which is dealing with precipitation
deficits this spring. Rainfall amounts will be less than 0.25" in
the lee of the Cascades increasing between 0.25-0.75" for the
lowlands over the eastern third of WA and North Idaho. HREF
probabilities for 0.50" vary from 70-100%. The strong winds
accompanying this system will drive up orographic rainfall amounts
in the mountains with 70-100% chance for receiving over an inch
of rainfall and expectations are amounts will be closer to 2" or
more along the immediate Cascade Crest and a few of the higher
peaks in North Idaho. Flood watches are in effect for Shoshone and
Lewis Counties where there is some potential for rapid rises on
streams and creeks and rock slides. Models are showing less
rainfall for Lewis County compared to the last few days which is
likely due to higher res modeling showing some downsloping off the
Wallowas of NE Oregon. If this trend continues, may be able to
adjust or remove the watch with future forecast updates.


Those venturing into the back-country of the Cascades should be prepared
for crashing snow levels. Snow levels are starting near 8000 feet
this afternoon and will be down closer to 4500 feet Monday
evening. A few inches of slushy accumulations will be possible
over Washington Pass but little to no accumulation is expected at
Stevens. Main impact will be to those in the back-country who do
not have proper gear, especially on the highest peaks where
amounts could be upwards of 6-12".

Swift westerly flow will be over the region on Tuesday as the upper-level
jet begins to buckle northward. One more wave will slip through
with a continued threat for light rain. Little to no rainfall is
expected in the lee of the Cascades with adequate lee side
shadowing. The Cascade Crest and Idaho Panhandle will intercept a
bulk of the moisture with potential for another quarter of an inch
or more. Tuesday will be another windy day with gusts down 5-10
mph compared to Monday and closer to the 30-35 mph range.
Sustained speeds will remain in the 15-25 mph range for our wind
prone areas across the Basin and adjacent areas.


Temperatures over the next few days will be on the cool side of normal
with highs only in the 50s to 60s. We will not have to worry
about freezing temperatures unless you are on the higher peaks.
Lows will be mild tonight remaining in the 40s and 50s then become
chilly dipping into the mid to upper 30s to mid 40s Tuesday and
Wednesday mornings. /sb

Wednesday to Sunday: The Inland NW will be drier and turning
warmer most of this period. A mid-level ridge gradually amplifies
over the region, somewhat held back by impulses riding through
southern Canada before Friday into Saturday. Then models start to
diverge on whether the ridge will persist or more troughy weather
comes in. From Wednesday to Friday look for transient higher
clouds, with a bit more in the way of high clouds Thursday as one
of those waves slide by southern Canada. A bit of flat cumulus is
possible around the mountains in the afternoon. Temperatures are
forecast to reach the upper 60s and 70s Wednesday, with some areas
approaching 80 in the deeper basin and L-C Valley. Thursday will
see more upper 70s and 80s, then mid-80s to mid-90s Friday into
Saturday. Saturday looks like the warmest day with some areas even
may areas pushing near 90 and perhaps near 100 in the deeper
basin. Ensembles show about a 15-25% chance of the 100 degree
readings occurring there; less than likely but still not out of
the realm of possibility. Any of this heat may cause some impacts
and some precautions may be needed to stay cool.

By late Saturday into Sunday some deeper moisture stats to
returns, with shortwave disturbance pushing near or through the
region. This will lead to some increased shower chances and may
some embedded t-storms. These first come to the Blues, Camas
Prairie and Cascade crest Saturday night and expand to more of the
region Sunday, but PoPs are still higher around the mountains.
Some guidance, particularly the Canadian model, shows a strong
system and broader precipitation chances Sunday (into next
Monday). However this model solution has been very inconsistent.
Precise temperatures next Sunday carry some lower confidence as
models show a model range in possible values. However the forecast
indicates some cooling over Saturday, with values remaining
easily above normal based on current solutions. /Solveig

&&

.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...
00Z TAFS: The leading warm front and plume of subtropical moisture
has reached the Inland Northwest with light rain reported across
most terminals as of 00z. As rain continues to fall, there is a
40-70% chance for MVFR conditions as the boundary layer moistens.
Probabilities have come down compared to previous runs. Areas
with moderate rainfall carry the greatest risk for visibility down
to 2-3SM. If this persists for several hours, conditions could
deteriorate to IFR for several hours. This comes with a 10-30%
chance. Rain intensities look to fluctuate at times between 9-13Z
for some areas. Rain ends from west to east 12-16z however this
will come with increasing winds and quick development of
convective showers. These showers will bring potential for strong
wind gusts from 16-22Z and could mature into thunderstorms with
isolated lightning strikes and small hail but by in large,
enhanced wind gusts under rain cores will be the largest concern
which could approach 50kts across the eastern third of WA and into
North Idaho. Widely scattered shower and isolated t-storms
continue across NE WA and N ID through Monday evening but strong
winds region-wide will be the most impactful weather element to
aviation.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence has
decreased some for timing and magnitude of the MVFR conditions.
This is a rare pattern for June so forecast continues to lean
in this direction but backed off on timing with 00z package.
Confidence is low to moderate for IFR conditions. There is also
uncertainty with the duration and/or breaks in precipitation
intensities within that 9-13z time-frame. Conditions could be
quite varying after 15z with developing convection. Would not rule
out lightning strikes and isolated stronger wind gusts near
convective downdrafts.


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

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        50  62  43  66  43  70 / 100  90  10  30   0   0
Coeur d`Alene  49  59  41  61  44  68 / 100 100  20  40  10   0
Pullman        50  58  42  62  44  67 / 100 100  10  30   0   0
Lewiston       56  68  48  71  53  79 / 100 100  10  20   0   0
Colville       47  62  38  63  37  71 / 100  90  20  60  10   0
Sandpoint      49  57  40  57  42  66 / 100 100  50  60  40   0
Kellogg        49  55  42  57  46  66 / 100 100  50  60  40   0
Moses Lake     52  68  48  74  44  77 /  80  50  10  10   0   0
Wenatchee      52  63  47  69  46  75 /  80  50  10  30   0   0
Omak           49  69  44  71  42  75 /  90  60  10  30   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory from 9 AM to 7 PM PDT Monday for Northern
     Panhandle.

     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 through Monday evening for Central Panhandle
     Mountains-Lewis and Southern Nez Perce Counties.

WA...Wind Advisory from 9 AM to 7 PM PDT Monday for Northeast
     Mountains.

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

&&

$$