Area Forecast Discussion
Issued by NWS Spokane, WA

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308
FXUS66 KOTX 210033
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
433 PM PST Mon Feb 20 2017

.SYNOPSIS...
More wet weather can be expected through Tuesday, leading to
moderate precipitation, higher snow levels and renewed concerns of
flooding. Cooler and showery weather is forecast for Wednesday
and continuing for the rest of the work. Drier but cooler weather
is forecast for the upcoming weekend.

&&

.DISCUSSION...
Tonight: A weather disturbance will continue to move north and
east through the evening hours. Rain and snow showers will
continue in that direction as well. Some showers through the late
afternoon may have some moderate to heavy rain as well as graupel.
By early this evening most of the showers should be confined to
the Cascades and NE WA and north ID. Southwest winds will continue
east of Ritzville into the Palouse through the evening hours at
15-20 mph before decreasing overnight. There could be some locally
stronger winds around Pomeroy and Alpowa Summit, but think they
will remain just below wind advisory criteria. In and around the
Blue Mountains the winds could be quite windy, but should remain
below the 40 mph high wind warning criteria. (we do not issue wind
advisories for the mountains) Winds may get as far north as
Spokane, but should be less than what is seen further south.
Through the overnight hours snow showers will be possible at the
crest of the Cascades as well as north ID close to the border.
There is another weather system moving into the region, but models
have slowed the timing of the onset of precipitation. Have
decreased our chance of precip overnight towards morning. Have the
best chance of precip with this next wave as far north as the
WA/ID Palouse around Pullman, but think the rain/mountain snow may
more likely be towards the Camas Prairie by 4am. /Nisbet

Tuesday and Tuesday Night: One more round of precipitation will
move through Oregon, Idaho, and eastern Washington Tuesday and
Tuesday night. This shot of rain and mountain snow will come at us
from the southwest with relatively mild temperatures across the
Palouse and southern Idaho Panhandle raising concerns for
more runoff and and subsequent flooding. Gusty winds and mountain
snow will also accompany Tuesday`s system.

* Flooding Concerns: The morning runs of the GFS, NAM, and
  Canadian models produce a swath of a half inch to an inch of
  precipitation across southeast Washington into the central and
  southern Idaho Panhandle. While the Washington Palouse has lost
  much of its snow pack, a good deal of snow remains over the
  Idaho Panhandle, the Idaho Palouse (especially above 3000 feet),
  and Spokane/CDA area. A Flood Watch remains in effect for
  counties with a good snow pack with the best chances for rain
  Tuesday and Tuesday night. If the models continue the trend of
  keeping most of our precipitation along and south of I-90, we
  may be able to drop the Flood Watch for southern Stevens and
  Pend Oreille counties.

* Freezing Rain: There is a chance that precipitation may begin as
  freezing rain Tuesday morning around Moses Lake, Ephrata, and
  Ritzville. The significance of this potential freezing rain
  episode will be dictated by the arrival time of the
  precipitation band. With the exception of the ECMWF, the models
  don`t produce much precipitation prior to 7am. If precipitation
  holds off until mid-morning, marginal temperatures and
  increasing pavement temperatures will limit icing on the roads.
  If precipitation develops prior to sunrise, we may have a couple
  hours of slick driving conditions around the Tuesday morning
  commute.

* Mountain Snow: For the central and southern Panhandle (where the
  majority of precipitation is expected), snow levels are expected
  to be in the 3000-5000ft range during the day Tuesday. We may
  see some slushy accumulations at Lookout Pass during the day,
  but impacts from snow accumulations will mainly be above most of
  our low and mid elevation roads during the day Tuesday.
  Conditions will likely change Tuesday evening into Wednesday
  morning as snow levels fall behind the departing low. Wet
  accumulations up to 2 inches will be possible above 2000-2500
  feet around Spokane, CDA, Kellogg, and Moscow. As the sun sets,
  accumulating snow will also have the potential to become more
  problematic at Lookout Pass and Fourth of July Pass on I-90.

* Gusty Winds: Stiff cold air advection, steep low level lapse
  rates, and a tight southwest pressure gradient across SE WA will
  likely produce sustained winds of 15 to 20 mph with gusts to 35
  mph at Pomeroy, Pullman, Moscow, LaCrosse, and Rockford Tuesday
  night into the early morning hours on Wednesday.

Wednesday through Friday: Our weather pattern will transition from
being on the northern periphery of the southern branch of the
Polar Jet (mild and wet) to being under a Polar trough. Cooler and
showery weather is expected Wed, Thu, and Fri. This pattern is
just what we need to decrease our rate of snow melt. Precipitation
will become more showery with snow levels as low as the valley
floors. /GKoch

Thursday night through Monday: Upper level trough will be over
the region with cooler than normal temperatures and occasional
showery conditions. Main jet stream will be focused south across
California and the southern tier states with a secondary northerly
jet in the Gulf of AK. There looks to be no good moisture taps
for the Inland NW, just a drier northwest flow aloft with
increased instability due to colder air aloft. There are a couple
of disturbances in the flow that are expected to spin up surface
lows in the eastern Pacific. The tracks and dynamics of these
features are forecast to remain off the WA/OR coasts and not
expected to impact the Inland NW too much except an increase of
mountain instability showers.  Temperatures will trend cooler
than normal for the weekend with sub freezing overnight lows and
chilly daytime highs in the 30s to lower 40s. These readings will
make it feel more like late January instead of late February
despite the longer daylight hours. Winds will be light and staying
predominantly out of the north. River levels will return to more
typical levels. This weather pattern will do little to increase
or decrease our current snow pack. /rfox.

&&

.AVIATION...
00Z TAFS: A band of rain and snow associated with a quick moving
low pressure system will exit the Idaho Panhandle and northeast
Washington beween 00z-02z. Look for increasingly gusty southwest
winds at KPUW, KGEG, KSFF, and KCOE. The gusty winds are expected
to disperse stratus allowing for some clearing this evening.
Another band of precipitation is expected to spread rain and snow
into the region from the southwest in the 12z-18z time frame.
Precipitation may begin as freezing rain at Moses Lake and Ephrata
before temps warm above freezing by late morning. For Spokane and
Coeur d`Alene, snow should transition to rain by early to mid
afternoon with little to no runway snow accumulation. /GKoch

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        31  39  26  38  22  35 /  80  70  70  20  20  20
Coeur d`Alene  31  39  28  37  21  35 /  80  80  80  30  20  20
Pullman        35  40  29  38  23  35 /  30 100  90  20  10  40
Lewiston       37  47  34  45  28  41 /  40 100  90  20  10  40
Colville       31  43  23  41  21  38 /  90  30  30  20  10  10
Sandpoint      30  40  30  38  22  35 /  90  50  60  30  20  30
Kellogg        32  38  28  35  22  34 /  90 100 100  60  30  50
Moses Lake     28  40  23  42  22  36 /  10  50  20  10  10  10
Wenatchee      28  39  25  40  23  35 /  20  30  10  20  10  10
Omak           27  39  21  39  21  35 /  20  20  10  20  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch through Wednesday afternoon for Central Panhandle
     Mountains-Coeur d`Alene Area-Idaho Palouse-Northern
     Panhandle.

WA...Flood Watch through Wednesday afternoon for Moses Lake Area-
     Northeast Mountains-Spokane Area-Upper Columbia Basin-
     Waterville Plateau.

&&

$$



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