333
FXUS66 KOTX 242208
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
308 PM PDT Fri May 24 2024

.SYNOPSIS...
Showers will continue across the Inland Northwest through
Saturday. Saturday will breezy with west to southwest wind gusts
of 25 to 30 mph. Dry weather returns on Sunday and Monday with
temperatures warming back into 70s and 80s. A return of cool, wet
weather is expected to return midweek.

&&

.DISCUSSION...
Tonight through Sunday night: The upcoming holiday weekend will start
off cool and unsettled with a transition to warmer and drier. The
cool and unsettled portion of the forecast comes courtesy of an
upper-level trough dropping into the region. The trough will come
in three pieces of energy. The first, generally southern branch is
currently crossing the Cascades this afternoon with light showers
filling in across Central WA and expected to slowly work eastward
this evening and overnight expanding across North Idaho and the
eastern third of WA. Precipitation amounts with this activity will
be light and around a tenth of an inch or less. Before this wave
arrives and clouds thicken, afternoon and early evening
instability will promote hit or miss showers and a few
thunderstorms. The latest RUC mesoanalysis is showing CAPES around
500 J/kg over portions of the North Idaho. We have yet to observe
any lightning but this will need to be monitored as we reach peak
heating. More organized bands of showers and thunderstorms are
forming over Northeastern Oregon this afternoon and will slowly
drift toward the Blue Mountains and Camas Prairie. This activity
typically struggles to survive as it comes off the higher terrain
but these areas are receiving some of the best sun so would not
rule out a few cells surviving before sunset. Brief downpours,
lightning, and wind gusts up to 35 mph will be the main concern
with any cells.

The second, northern branch of the trough swings across Northern WA
and North Idaho on Saturday. The orientation of the midlevel jet
across the barrier results in pressure falls in the lee of the
Rockies across southern Alberta tightening the pressure gradient
across the Inland Northwest. There remains some differences with
the exact magnitude of the cross-CWA pressure gradient resulting
in a 10 mph difference in potential wind gusts for Saturday
afternoon and early evening. The European model and ensembles
remain on the windier side of the spectrum with the GFS and
ensemble members on the lower end. Each agree with windy
conditions but the difference in wind gusts varies from 30-35 mph
(EC) to 20-25 mph (GFS) for much of the Basin, West Plains, and
into the Palouse. Each agree on locally stronger winds coming
through the Cascade Gaps and on to the Waterville Plateau which
carries a 50% chance for wind gusts in excess of 30 mph. As for
precipitation, the main concentration of showers will be over the
northern mountains and into the Upper Columbia Basin. This will
correlate with the location of the coolest 500mb temperatures.
With ample sun breaks, CAPES could increase near 300-400 J/kg
bringing another threat for weak isolated thunderstorms during the
afternoon and early evening. Brief downpours, lightning strikes,
and wind gusts to 30 mph will remain the main hazards with any
cells.

The third and final piece of energy within this mean trough will
come through Sunday morning keeping a mention of light showers
but overall trends will be for trough to begin shifting east with
500mb temperatures warming from west to east throughout the day.
Thinking any showers for the northern mountains will be early in
the day with clouds shrinking with time.

Temperatures over the weekend will warm into the upper 50s to 60s
Saturday then 60-70s on Sunday. Overnight lows will be warmest
tonight (40s) with the heavier cloud cover then cool into the
30s-40s for Saturday night and Sunday night. Patchy frost will be
a concern for our sheltered northern valleys around Republic,
Colville, and Priest Lake Saturday night into Sunday morning. /sb

Monday through Friday:
A ridge across the Inland Northwest will lead to warm and dry
conditions on Monday. Monday and Tuesday will likely see the warmest
temperatures of next week. These warm and dry conditions are not
anticipated to last long, however, as a cold front and associated
low pressure is anticipated to move into the region mid-week. This
will also lead to breezy westerly winds for Tuesday night through
Wednesday night. Daytime temperatures will likely drop back below
seasonal norms for the second have of the week. Daily precip chances
will favor NE WA and N ID, with little appreciable precip
anticipated across the Columbia Basin. /KD

&&

.AVIATION...
18Z TAFS: Upper level trough dropping into the region will result
in building cumulus clouds through the afternoon with spotty
showers across the northern mountains and extreme SE WA and the
lower Idaho Panhandle. There is a 10-20% chance for t-storms
around the Blue Mountains and Camas Prairie. For Lewiston proper,
percentages are closer to 10% leading to low confidence to include
in the 18Z TAFS. Energy with the upper-level disturbance will
swing through overnight with a band of showers but largely VFR
skies. Added prob30 groups to account for this activity. This will
also come with a 20-40% chance for brief MVFR ceilings with the
highest probabilities along an axis from Pullman,WA to Mullan, ID.
Winds will remain elevated overnight at 10-15 mph. Winds will
continue to increase on Saturday mainly after 18z.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is moderate confidence (50% chance) for showers at times
across the Idaho Panhandle, Northeastern WA, and between the Blue
Mountains and Camas Prairie. Confidence is low for lightning
coverage as any storms come off the higher terrain of NE OR into
the lower Idaho Panhandle. A few models indicate a small potential
(10%) for a few lightning strikes overnight with the showers.
Confidence is low for MVFR conditions overnight given the
increasing winds. Feel best chances will be around St Maries,
Kellogg, and Mullan.

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

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        46  61  40  64  44  73 /  30  30  10   0   0   0
Coeur d`Alene  45  59  39  61  44  72 /  60  50  10   0   0   0
Pullman        43  57  38  62  43  72 /  40  20   0   0   0   0
Lewiston       49  66  44  70  49  81 /  40  30   0   0   0   0
Colville       45  61  33  64  37  73 /  40  80  30  10   0   0
Sandpoint      45  57  39  59  42  69 /  60  80  40  10   0   0
Kellogg        44  55  41  57  45  71 /  70  80  30  10   0   0
Moses Lake     45  68  41  72  44  79 /  20  10   0   0   0   0
Wenatchee      44  65  45  68  48  77 /  20   0   0   0   0   0
Omak           48  69  39  69  45  77 /  30  30   0   0   0   0

&&

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

$$