242
FXUS66 KOTX 041143
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
443 AM PDT Fri Apr 4 2025

.SYNOPSIS...
High pressure builds over the region delivering a warming and
drying trend Friday into the weekend. Rain returns to the
region Sunday into Monday morning. Monday afternoon and
Tuesday will feature cooler temperatures, breezy winds, and
on and off showers.


&&

.DISCUSSION...
Friday through Sunday: The Inland NW will be treated to a period of
dry conditions with the passage of an upper-level ridge. The
ridge axis is currently along 130W with northerly flow allowing
drier, continental air to invade from the north. Dewpoints in
north central WA have dropped into the teens to lower 20s with
higher observations in the single digits. The northerly push is
weak but will allow the drier air to continue to spill southward
over the next 12 hours. I anticipate some cumulus buildups again
today but the depth of the clouds will be shallow as 500mb
temperatures warm and any hydrometeors that fall in North Idaho
and far E WA will encounter the drier air in the lower-levels
resulting in virga vs precip. The ridge axis will shift over the
Cascades on Saturday and begin to slide east by Sunday. Main
impacts will be increasing mid and high clouds Sunday with rain
expected to return to the region Sunday night.

It will be dry in the afternoon with humidity levels between 20-30%.
Use caution if burning near dry grasses from 2024. Winds will be
light today and Saturday with speeds of 5-10 mph then increase
from the south/southeast on Sunday near 10-15 mph and gusts to 20
mph over the Upper Columbia Basin and into the Okanogan Valley.

The drier air will result in chilly morning lows dipping into the 20s
to lower 30s each this morning (FRI) and again Saturday morning
with around 3-5 degrees of warming by Sunday morning. Be sure to
protect any sensitive plants. Highs will be quite pleasant
starting off in the 50/60s today, 60s Saturday, and then 60/70s
Sunday.

Sunday night through Tuesday: 100% of the ensemble suites support a
progressive pattern with the ridge sliding east and a moisten
laden trough reclaiming the Northwest. Clouds will thicken through
the day Sunday with precipitation expanding into the Cascades
Sunday night and spreading east into E WA and N ID by early Monday
morning. PWATS increase to 180-215% of normal and with midlevel
flow initially out of the south, don`t expect much of a rain
shadow in the lee of the Cascades with the onset of the precip
Sunday night. NBM comes with 50-80% chance for at least 0.01 and
20-30% chance for a tenth for locations like Wenatchee, Winthrop,
Omak, and Moses Lake. Given the southerly flow, there could be
highly localized downsloping off mission ridge into Wenatchee
proper. As the precip expands east into E WA and N Idaho, precip
amounts of at least a tenth increase toward 30-50% and 70% or
greater for at least 0.01. Current forecast calls for 0.20-0.40"
for most areas east of a line from Republic to Omak and 0.05-0.15"
in the lee of the Cascades. Snow levels will start off high with
mainly rain for the mountain passes through Monday afternoon.

Once the trof carves into the NW Monday afternoon, upper-levels will
cool and instability showers will be possible from a combination
of orographic flow, pockets of clearing, and additional shortwaves
rotating through the mean trof. Nearly all deterministic models
indicate these additional shortwaves but exact track and timing is
uncertain, differing by as much as 50-80 miles and 6 hours. This
will play a role where thunderstorms will occur Monday afternoon
as well and latest consensus is NE WA and N ID but would not rule
out other areas. A reinforcing shortwave, slightly deeper than the
aforementioned waves is progged to swing into the NW on Tuesday
with additional, organized showers and reinforcing shot of cooler
air.

Snow levels by Monday evening into Monday night will dip 3500-4000
feet in the Cascades and 4500-5500 feet in North Idaho with snow
showers on the mountain passes and 20% chance for an inch of snow.

This period will feature breezy to gusty winds as air masses are
transitioning.  Our wind prone areas in the lee of the Cascades,
across the Basin, Palouse, and West Plains come with a 40-50% chance
for wind gust of 30 mph or higher but only 5-10% chance for
reaching 40 mph. This is reflected in the ensemble members which
are tightly clustered closer 25-35 mph and maybe 1 or 2 members
showing a gust reaching 40 mph. Monday and Tuesday afternoon will
each feature these elevated winds.

Wednesday into next weekend: There is a lot more uncertainty with
details in the forecast for mid to late week. Cluster analysis
shows a 50/50 split in the 100 member ensemble whether a ridge
rebounds over the NW or a trough remains carved into the
Northwest. Nearly 50% of the variance in the models relates to the
placement of the ridge. If the ridge axis sets up closer to the
spine of the Rockies, this will leave the NW exposed to systems
while further west will allow for a few days of drying. Further
examination of the multi-model ensemble suggests: a progressive
pattern looks to remain in place over the E Pac and as you go
further in time, its just a matter of when the ridge shifts east
and next trough arrives. So would not rule out a few days of
drying but hard to pinpoint any long duration event. /sb

&&

.AVIATION...
12Z TAFS: Dry northerly flow over the region is delivering VFR
skies for Central WA. The drier boundary layer dewpoints have yet
to fully penetrate into all of E WA and N ID. Clear skies have
resulted in areas of radiation fog within the Coeur d`Alene and
St Joe river valleys and patchy coverage around Priest Lake,
Newport, Coeur d`Alene, and Spokane river. Also observing shallow
fog on the West Plains southward toward Pullman but confidence is
low for any activity to impact the TAF sites before 16z. With the
exception of some shallow cumulus clouds this afternoon, skies
will be mostly clear. Winds will be light as well under high
pressure.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high
confidence in VFR through Saturday morning for Omak, Chelan,
Wenatchee, and Moses Lake. Confidence is lower for valleys of NE
WA and N ID which will contend with patchy to scattered fog prior
to 16z. There is a 10% chance for this to create restrictions at
KGEG and 20% at KSFF/KCOE. /sb

-----------------------
Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        56  31  62  37  67  46 /   0   0   0   0   0  30
Coeur d`Alene  55  27  60  34  66  43 /   0   0   0   0   0  20
Pullman        54  30  59  37  65  45 /   0   0   0   0   0  30
Lewiston       60  34  65  40  72  48 /   0   0   0   0   0  20
Colville       57  27  61  32  65  44 /   0   0   0   0   0  40
Sandpoint      52  28  59  32  63  42 /   0   0   0   0   0  20
Kellogg        51  26  57  34  63  43 /   0   0   0   0   0  10
Moses Lake     62  30  65  38  70  48 /   0   0   0   0   0  50
Wenatchee      60  36  63  42  66  47 /   0   0   0   0   0  60
Omak           60  30  64  36  68  46 /   0   0   0   0   0  60

&&

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

$$