Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 201134
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
334 AM PST Mon Feb 20 2017

.SYNOPSIS...
The weather pattern will remain unsettled and stormy through
early this week. A pair of mild and wetter weather systems are
expected Today and 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.

&&

.DISCUSSION...
Today and Tonight: A lot of weather to consider in the next 24
hours. The cause of all of this weather is yet another Pacific
storm, currently making landfall in southwest Oregon. Water Vapor
imagery is rather impressive at the moment with a good darkening
dry slot. This system is complements of a nice 160kt jet off the
northern CA coast. Precipitation should arrive into the lower
Basin shortly after sunrise, spreading in the Spokane area around
10am. Given this morning arrival time, the precipitation type will
mainly be snow or a rain/snow mix, changing to all rain in the
afternoon for the valleys. The frontal band will move into the
northern mountains before noon, mainly in the form of snow. Cold
air trapped along the Cascades will keep the precipitation as all
snow for those valleys as well as Omak and Wenatchee, where an
inch or 2 of accumulation is expected.

In the afternoon, the frontal band moves north and things start to
get interesting. The aforementioned dry slot will move across
southeast WA and the southern Panhandle. This will do a few
things: provide a little sunshine to warm temperatures into the
lower 50s. This will allow the atmosphere to destabilize enough
for a chance of thunderstorms over the Palouse, Camas Prairie,
into the southern Panhandle. This dry slot will also bring some
good momentum with it. The warm temperatures will allow mixing up
to 5000 feet which will bring in some rather gusty afternoon winds
on the Palouse. In general, any thunderstorms that do form will
be short-lived and not much to write home about. But there`s an
outside slim chance that a thunderstorm could mix down some higher
momentum air that could cause gusts into the 40-50 mph range over
a very localized area.

All this activity will shut down early in the evening as the storm
exits into BC. The next wave may start to move into the forecast
area late Monday night.  RJ


Tuesday: Models are shifting their tune a bit resulting in a low
confidence forecast with respect to the details. A low pressure
system will track across the region, but there is variability with
how it will track. The ECMWF is furthest north with the low
tracking from around Portland, OR in the morning and into the
Northeast Mtns in the afternoon. The GFS model has been tracking
the low further and further south with each run. The 00Z run off
of the GFS now has the low tracking across southeast WA and into
the Central Panhandle Mtns. The 00Z NAM is more similar to the GFS
and the Canadian more similar to the ECMWF solution. Temperatures,
snow levels, and the axis of heaviest precip will be dependent on
which track is more correct. I did trend toward the GFS with the
axis of heaviest precip more across southeast WA and into the
Central ID Panhandle. I also lowered snow levels a bit and dropped
high temperatures a bit as well. Instead of highs getting up into
the lower to mid 40s, we are looking at highs in the upper 30s for
most places. There will be a better chance for snow mixing in as
well, especially Tuesday evening/night across the southeastern
portion of the forecast area as the low exits. This lowers to
potential for flooding impacts as we do not look to as mild, so
snow melt will be less of an issue as previously thought. There is
still the potential for moderate rainfall, mostly across the
southeast WA and into the Central Panhandle Mtns. That rain looks
to switch over to snow above 2,000 feet Tuesday night with 1-3
inches possible for places like Pullman, over to St. Maries,
Kellogg, Wallace and on the Camas Prairie. The Central Panhandle
Mtns will see moderate snowfall accumulations and snow looks more
likely over Lookout Pass through the day on Tuesday with 4-7
inches possible.

Tuesday night through Friday night: An upper level trough of lower
pressure will move over the region. Weak instability during the
day will result in snow showers. Temperatures will be colder and
drop back down below normal for mid February. Patchy fog will be
possible Wednesday and Thursday nights as showers decrease in the
evening and skies clear. Best chances for fog will be in the
mountain valleys and over the Upper Columbia Basin and Spokane
Area. /SVH

Saturday and Sunday: Saturday looks mostly dry as we get a break
between systems, but the next low pressure center begins its
track down the west coast by Sunday bringing the moisture back
with it. Models differ on the exact track but it looks to stay off
the coast until well south of us. This would spare us from the
bulk of the precip, though the showery regime remains, especially
for the mountain zones on Sunday. Any showers will fall as snow,
with snow levels near valley floors through the weekend. Continued
northerly flow will keep us below average, with highs in the 30s
and lows in the teens. /bwilliams

&&

.AVIATION...
12Z TAFS: Another Pacific storm system will move over the area
today. It will bring morning rain or snow to the TAF sites with
afternoon rain showers. There`s an outside chance of a
thunderstorm at KPUW or KLWS this afternoon, but too low of a
probability to include in the TAF. But gusty afternoon winds are
likely at these two TAF sites. All of the weather should wind down
after sunset for a quiet evening before the next Pacific system
starts to move in early Tuesday morning. RJ

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        42  32  38  28  37  21 / 100  90  90  50  30  20
Coeur d`Alene  42  31  38  28  36  21 / 100 100 100  80  40  30
Pullman        49  36  41  30  37  25 /  90  50 100  90  40  30
Lewiston       53  37  45  33  43  29 /  80  40 100  90  30  20
Colville       39  31  38  25  37  21 / 100  90  70  30  30  20
Sandpoint      39  30  38  28  36  23 / 100 100  90  60  50  40
Kellogg        40  32  37  29  35  23 / 100  80 100 100  60  40
Moses Lake     39  28  38  26  38  22 /  90  30  70  10  10  10
Wenatchee      35  28  38  28  35  22 / 100  40  60  10  10  10
Omak           37  28  35  25  35  21 /  90  50  40  10  20  10

&&

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

WA...Flood Watch from noon PST today through Wednesday afternoon for
     Moses Lake Area-Northeast Mountains-Okanogan Highlands-
     Okanogan Valley-Spokane Area-Upper Columbia Basin-
     Waterville Plateau.

&&

$$


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