Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 282127
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
227 PM PDT Tue Mar 28 2017

.SYNOPSIS...

Rain and mountain snow will continue this evening. This comes
ahead of another round of widespread moderate precipitation that
will arrive overnight and last until early Thursday. This may
aggravate flooding issues. Friday will bring a dry break period
before more unsettled weather for next weekend.

&&

.DISCUSSION...

Tonight thru Wednesday night...Our next system and strong
moisture fetch are evident on water vapor imagery as of late this
afternoon. A warm front lifting through the region will provide
mild overnight lows and good isentropic lift for an expanding
precipitation swath through the overnight hours. The previously
mentioned moisture fetch/atmospheric river will allow PWATs to
rise to 0.6 to 0.9, or well into the 90th percentile. Rain will be
the predominant precipitation type from this system with snow
generally above 4-5k feet. By Wednesday night and into Thursday
morning, the best moisture fetch begins to sink to the south and a
cold front will sweep through the area. This will focus the best
chances for continuing precipitation over the central Idaho
Panhandle and far southeast Washington.

Precipitation totals continue to look healthy and have been
trended upward some with this forecast package, especially across
the southeast zones (where NAEFS and GEFS climatological anomalies
are highest) and across the mountains of the Idaho Panhandle and
NE WA mountains. In general, look for 0.4 to 0.7 inches across the
eastern 1/3rd of Washington, 0.6 to 0.9 across the Panhandle
valleys and in excess of an inch of liquid in the mountains. The
deep Basin and Wenatchee area will probably see the lightest
totals as the isentropic lift looks weakest in this area. The
immediate Cascade crest will likely see liquid amounts in the 1 to
2 inch range with some of that being tied up as snowfall in the
higher elevations.

Impacts: The additional rainfall will likely continue to aggravate
ongoing flooding issues. At this time, hydrographs for the main
stem river show some response, but don`t deviate much from their
general ongoing trends. Smaller streams and rivers, such as the
Little Spokane River at Dartford and Paradise Creek at Moscow,
will likely react with rises and low-land and lake flooding will
continue to be an issue. The other area of concern will be the
continued risk of mud and landslides in steeper terrain,
especially across far eastern Washington and the Idaho Panhandle.
For these reasons, a Flood Watch has been issued for portions of
northeast Washington and all of our Idaho Panhandle counties.
/Kalin

Thursday to Friday night: The Inland NW will remain in a
showery pattern, before a ridge of high pressure dries things out
for most of the region Friday, but there will be localized
exceptions.

First between Thursday morning and Thursday evening a stretching
upper trough will migrate across the western United States. This
will provide the Inland NW will broad-scale lift and unstable
lapse rates and some pockets of weak afternoon/evening CAPE. At
the surface a boundary stretched across southeast WA and lower ID
early Thursday will edge away. However a deformation axis wraps
back from a surface low sitting over the High Plains and trails
across north Idaho into central Washington. All these factors will
mean a threat of showers, with the highest risk around the
mountains and southeastern WA/ID and smaller chances back into the
Columbia Basin/northeastern WA. The risk will wane through the
evening.

As for thunderstorms, I`m not seeing any indication that instability
will be strong enough to warrant an inclusion. Overall precipitation
amounts will be highly variable, with some areas in a showery
set-up not seeing anything. The higher risk locations, especially
the southeastern CWA and mountains may stand a chance of seeing
some locally moderate precipitation amounts. Snow levels will be
around 3.5-4.5kft so this will mean the potential for some snow in
the mountain passes but impacts may be limited by the showery
nature. It will be locally breezy from the west to northwest,
especially toward the western and southern CWA but this too should
not be strong enough to have any significant impacts.

Then late Thursday evening and overnight, continuing into Friday,
deeper subsidence and more stable conditions start in. This will
shut off the threat of precipitation for most of the region. The
main threat of any linger showers will be over the Idaho Panhandle
mountains in the westerly flow. Friday night into Saturday
morning the flow starts to flatten with another system approaching
from the west. This will lead to some increasing middle to high
clouds from the west. A slight chance of precipitation will also
return to the Cascade crest overnight. Patchy fog will be a threat
in the sheltered northeastern WA and ID Panhandle valleys
Thursday night/Friday morning and again Friday night. /J. Cote`

Saturday through Tuesday: The upper level jet stream and
associated dynamics will be primarily directed toward southern BC
on Saturday. A cold front will push across the region, but
without much support from aloft, it doesn`t appear that this front
will bring much in the way of precipitation. The upper level
trough is then progged to dig in over the region Saturday night
into Sunday. The atmosphere is expected to be conditionally
unstable by this point with showers likely expanding in coverage
through the afternoon on Sunday. Temperatures will be a bit cooler
as well with our coldest night in the extended expected Sunday
night.

Shortwave ridging will build in over the region for the beginning
of next week, which is expected to result in a drier period for
Monday into Tuesday. However, models are in decent agreement with
fair confidence for more precipitation to return to the region
around the middle portion of next week. Another upper level low
pressure system is set to develop in the Gulf of Alaska. This will
direct a better tap of Pacific moisture into the Inland
Northwest. Snow levels will potentially rise above mountain tops
with rain at mid elevations and snow changing over to rain at
higher elevations as well. Although confidence is low for any
specific impacts, this will be another period to look to for
additional flood impacts/rock and mud slides across the region.
/SVH

&&

.AVIATION...
18Z TAFs: SCT-BKN clouds with bases 1500-2500 have been observed
at KCOE/KSFF/KGEG/KPUW this morning due to light precipitation as
indicated on WSR-88D. CIGs may fluctuate from MVFR to VFR at this
locations during the day. Clouds will thicken overnight and
moderate precipitation will develop after midnight with MVFR CIGs
expected at most TAF sites. Wister/WFO Pendleton

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        40  51  39  52  35  55 /  80 100  70  40  10   0
Coeur d`Alene  38  49  38  50  34  53 /  80 100  80  50  10   0
Pullman        41  51  41  49  34  52 /  60 100  90  60  20   0
Lewiston       44  56  43  54  37  56 /  50  90  90  60  10   0
Colville       40  48  37  52  34  55 /  90 100  60  40   0   0
Sandpoint      37  47  35  49  33  52 /  90 100  90  50  10   0
Kellogg        37  46  37  46  33  50 /  70 100  90  70  30  10
Moses Lake     44  58  40  59  34  60 /  80  80  30  20   0   0
Wenatchee      42  54  38  55  34  58 /  80  80  20  10   0   0
Omak           41  52  36  55  33  58 /  80  90  30  20   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch from late tonight through Friday morning for Central
     Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse-Lewis
     and Southern Nez Perce Counties-Lewiston Area-Northern
     Panhandle.

WA...Flood Watch from late tonight through Friday morning for Lower
     Garfield and Asotin Counties-Northeast Blue Mountains-
     Northeast Mountains-Spokane Area.

&&

$$


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