Lewiston, Idaho 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

099
FXUS66 KOTX 112235
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
335 PM PDT Fri Apr 11 2025

.SYNOPSIS...
Today looks to be a dry day across the region, followed by cool
and showery weather on Saturday. This weekend will also bring
colder overnight low temperatures. Temperatures will then trend
back upward heading into the early to middle part of next week.

&&

.DISCUSSION...
Tonight: Very localized shower chances and some cloudiness will be
found over the Inland NW. The area sits in a southwest flow ahead
of an offshore trough. The jet stream stretches across the
southern CWA and a boundary is stalled nearby. Just southeast of
the boundary is a modest fetch of moisture. Some impulses riding
along that boundary will be close enough to bring some shower risk
to the Blue Mountains and Camas Prairie. A smaller risk is found
toward the L-C Valley into southern Shoshone county, around 10%.
Meanwhile the trough axis and moisture associated with that will
be edging toward the Cascades. That moisture is not as deep. While
PWATS near the SE CWA are near 150-200% of normal, those with
that offshore trough feature are near 80-110% of normal. Clouds
will increase from the west while a chance for snow showers,
possible mixed with rain, come to the Cascade crest late this
evening into the overnight. Winds will start to increase near the
Cascades and Waterville Plateau, as well as near the downwind of
the Blue Mountains, overnight into early Saturday morning. Lows
will largely be in the 30s, with some upper 20s around the
Cascades and areas near 40 over the L-C Valley and deeper basin.

Saturday: The offshore system and its supporting upper trough axis
shifts through during the day. This will expand some rain/snow
shower chances around NE WA/north and central ID in the morning
and continue the risk near the Cascades. By late morning to early
afternoon continuing into the late afternoon, the upper trough and
expanding instability will lead to a broader threat of showers
around the region. The best chances (60-90%) remain in the
mountain zones, but some modest risk (30-60%) expand over the
eastern third of WA. Meanwhile the lee of the Cascades and
western basin will be mostly dry, with the potential for showers
only near 5-20%. By evening the primary precipitaiton chances
retreat to Idaho and near the ID/WA border, closer to the
Spokane/C`dA area, then end late evening into the overnight.

Thunderstorms risk: a couple hundred J/kg of CAPE over NE WA and
ID will mean some risk for t-storms, with the best risk from
about 1 PM to 7 PM. The thing to watch out for those will be gusty
winds, as the background atmosphere will be already breezy/gusty.
The lower atmosphere will be dry, with an inverted-V looking
sounding. The CAPE is tall and skinny, so if there is any hail it
would likely be small.

Precipitation-type and amounts: This will be mostly mountain snow
and valley rain chances by then, but some snow could mix in to
the valleys too for any showers that develop earlier in the day
and/or are heavier in nature. Some convective instability is in
place so there is some risk for embedded t-storms over the
northeast third of WA and ID in the afternoon. Given the limited
moisture, precipitation amounts are generally light from trace
amounts to 0.05". Locally higher amounts can be expected in the
mountains and any t-storms could produce localized heavier
amounts too. As for the snow amounts, the main accumulation will
be in the mountains. However some could be found in the higher
Cascade valleys too. In the mountains themselves snow amounts will
generally be less than 1"; except the Cascade crest which could
see up 2" inches. However accumulation on roads will be limited
during the daylight hours, so impacts should be low if any. Highs
will be the upper 40s and 50s, with a few areas near 60 in the
deeper basin.

Winds: the other notable feature of the system will be the winds.
The cross-Cascade gradient increase tonight into Saturday and
start to slacken Saturday night. Wind start to increase throughout
the area in the morning and peak in the afternoon hours, before
starting to decrease through evening. They will strongest near the
lee of the Cascades into the western basin and near and downwind
of the Blue Mountains onto the Palouse/L-C valley. I did mix them
with the NBM 75-90% percentile over the mean NBM. Speeds of 15-25
mph are forecast, with some areas possibly seeing sustained winds
near 20 mph around the Waterville Plateau, southern Okanogan
Valley and near the Blues. Gust of 20-40 mph are possible, with
local gusts to 45-50 mph with the stronger sustained winds.

Sunday to Friday: heading into the new work week the area will be
in drier and more progressive flow. After Saturday`s system tagger
could be some patchy fog in the sheltered valleys early Sunday
morning. The next weak system moves by between Tuesday and
Wednesday and another approaches the coast by the end of the week.
Look for some limited rain/snow shower chances near the mountains
Wednesday and again Friday near the Cascade crest. Some breezy
conditions are forecast around the areas the afternoon hours
Tuesday, Wednesday and Friday with gusts in the 15-20 mph range.
Otherwise look for dry weather with a mix of sun and clouds.

As for temperatures, morning lows will start off chilly Sunday and
Monday morning, with 20s and 30s. Sunday morning looks like the
coldest. So we are still not done with frost weather. Remember
the average last freezing temperature in Spokane is not until the
end of April. Temperatures then start trending warmer, pushing
above normal lows in the 30s and 40s and highs in 60s and 70s.
There is one day that trends cooler and that is Wednesday behind
the passing weak wave. /Solveig


&&

.AVIATION...
00Z TAFS: Mostly VFR conditions, but breezy with some shower
chances developing Saturday PM. Heading into overnight and
Saturday a system moves in, with a few more clouds and limited
shower chances largely near the mountains before 18Z, Chances
expand over most TAF sites between 18-00Z, with the exception of
EAT/MWH. Some embedded t-storms are possible Saturday PM over NE
WA/ID too, but they would be weak. The main impact could be gusty
winds. Of more note will be an increase in winds heading into
Saturday. Some LLWS is forecast near EAT/MWH toward 10-15Z
Saturday as the cross-Cascade gradient tightens with the incoming
trough, before mixing starts. Otherwise wind gusting near 20-30kt
will be possible after about 1400-1700 through Saturday evening.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence
in VFR conditions. Moderate confidence in LLWS near EAT/MWH and
low confidence in LLWS at PUW/LWS early Saturday (10-16Z).

-----------------------
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        36  54  31  58  33  64 /   0  30  10   0   0   0
Coeur d`Alene  35  51  30  56  31  64 /   0  50  20   0   0   0
Pullman        36  49  30  53  33  63 /   0  20  10   0   0   0
Lewiston       41  57  35  61  36  70 /  10  10   0   0   0   0
Colville       33  54  29  59  31  63 /   0  40  10   0   0   0
Sandpoint      36  49  30  54  31  60 /   0  70  20   0   0   0
Kellogg        38  46  31  52  33  62 /   0  70  30   0   0   0
Moses Lake     36  59  31  62  36  69 /   0  10   0   0   0   0
Wenatchee      38  55  34  60  39  64 /   0   0   0   0   0   0
Omak           36  58  31  62  35  66 /   0  20   0   0   0   0

&&

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

$$