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000 
FXUS66 KOTX 231230
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
430 AM PST Thu Nov 23 2017

.SYNOPSIS...
Wet and unsettled weather will linger through the week as a 
series of storm systems brings several rounds of precipitation to 
the region. Snow levels will be quite high through today allowing
motorists to travel over mountain passes on wet pavement. Cooler
and unsettled conditions this weekend will result in lowering 
snow levels just as travelers are heading home this weekend. Windy
conditions are expected today across the exposed areas of the 
Basin, Palouse, and north into the Spokane-Coeur D'Alene area.


&&

.DISCUSSION...
Today through Saturday morning...Satellite observations are telling
the story this morning. The ridge axis is pushing to the east and
flattening as the upper level low begins to move into the region.
The fire hose (atmospheric river) that has been over the region 
will sag south and give one more shot of deep Pacific moisture 
today. In addition there is a pretty decent wave running up along 
the cold front that will enhance the precipitation across the 
region today. The cold front will move across the region this 
afternoon and be southeast of the forecast by this evening. 
Southwest-west winds will result in rain shadowing off the 
Cascades and will keep rain amounts to a minimum for the lower 
east slopes and the western basin. For the remainder of the 
forecast area we can expect another period of light to moderate 
stratiform rain. Rain amounts from one to two tenths will be 
possible for the lower elevations outside of the basin and for the
Okanogan Highlands. The Cascades and Panhandle mountains will see
from a half inch to just over an inch through Friday morning. 
Precipitation will turn to showers behind the front with the focus
across the Cascades and Panhandle mountains. Snow levels will 
lower to 3000-4000 feet across the north and just above 4000 feet 
across the south. The mountains will get a chance for some snow 
tonight and Friday with the higher Cascades picking up 3-7 inches 
of fresh snow and the Panhandle mountains picking up 1-3 inches. 
Temperatures today will be 10-20 degrees above normal, before 
dropping 10-15 degrees Friday behind the cold front. These temps 
will still be on the warm side of normal

Next we look at winds with the cold front this afternoon. Pre-frontal
winds will be on the increase this morning out of the south- 
southwest with sustained winds 10-20 mph. As the front moves 
through the region winds will increase out of southwest with 
sustained winds 20-35 mph with gusts 35-45 mph and locally to 50 
mph. These higher winds will be mainly across the Columbia basin, 
the Palouse, The West Plains, and the Spokane-Coeur D'Alene 
corridor. Ridge top winds will also be very strong with gusts 
45-55 mph and locally gusts to 60 mph and more. 

* Impacts: A Wind Advisory has been issued for a portion of the
  forecast area from 11 AM this morning to 5 PM this afternoon.
  Driving on almost any roads will be difficult and especially for
  high profile vehicles. Tree damage is likely and downed power
  lines will be possible.
  
* Moderate rain on a deep snow pack will result in significant run
  off into area stream and small rivers. Flood watch are currently
  in affect of the Stehekin river in the Cascades and for Paradise
  Creek near Moscow ID. All small rivers and streams will continue
  to have high flows until the temperatures cool down on Friday.
  Lastly, be prepared for snow at pass levels in the Cascades. Tobin

Saturday through Sunday: A shortwave disturbance will ride up a
longwave trough of lower pressure in the Gulf of Alaska with a
surface low developing on the Pac NW coastline. Moist isentropic 
ascent will increase over the region Saturday evening. The timing 
of the precip is slower than previous model runs, but all models 
agree on delaying the passage of the warm front. With the surface 
low quite a bit offshore, best chances for precip will be across 
the northwest portion of the forecast area. Easterly winds will 
increase creating downsloping off of the higher terrain in the 
Central Panhandle Mtns with the southeast portion of forecast area
likely receiving little to no precip Saturday night. Strong warm 
air advection will keep snow levels high with snow mainly limited 
to the mountains of eastern WA. Even these mountain locations will
see snow transitioning over to rain as snow levels increase 
through the night. Temperatures will likely be quite mild over the
southeast portion of the region with 850 mb temps climbing to
between 11 and 12 Celsius and winds remaining breezy.

There is some question what the precip type will be in the Methow
Valley. The NAM is more aggressive with cold air remaining damned
up into this valley. However, looking at a NAM model sounding at 
this location, it shows a layer of low stratus hanging around 
through the afternoon. I am not sold that we will see enough cloud
cover to prevent temperatures from warming up in the afternoon, 
so I am going with rain and above freezing temperatures up the 
Methow Valley. The timing of the cold front is in question. The 
00Z GFS is much quicker with a Sunday morning frontal passage, 
whereas the 00Z ECMWF continues with the consistent message of 
slowing down this weather system. I am leaning more toward the 
ECMWF solution with a Sunday afternoon cold front passage. The 
cold front will switch winds more westerly with precip likely 
across extreme eastern WA and into the ID Panhandle. It also will 
result in increased winds. Breezy to windy conditions are 
expected, but not as strong as what we have forecasted for 
Thanksgiving.

Sunday night through Wednesday: The upper level trough of lower
pressure over the Gulf of Alaska will eject across the region
Sunday night into Monday. Models are consistent with the bulk of
the upper level dynamics now diving further south. So, this will
be a period where temperatures will drop, but it does not look as
wet as previously forecast. Lapse rates will steepen with colder
air moving in aloft. This will mean that the region overall will
be under a more unstable atmosphere and any little ripple that
comes across will have the potential to set up some showers. The
Panhandle will be favored for these shower and should see snow
levels lowering with snow the favored precip type at the passes.
The longer range medium range model guidance is looking a bit more
ridgy by the middle of next week with trend toward drier weather.
/SVH

&&

.AVIATION...
12Z TAFS: The biggest concern for today and this evening will be
increasing south-southwest associated with an incoming cold front.  
LLWS is in the forecast this morning for many of the TAF sites as
the cold front approaches the region. Widespread wing gusts 30-40
kts are expected at all the TAF sites between 20-03z. At KGEG 
wind gusts 40-45 kts will be possible. Winds are expected to
decrease significantly after 04-06z. Expect short periods of
moderate to heavy rainfall as the front moves from west to east
today. For early this morning stratus/fog will drop conditions to
IFR/LIFR at KMWH/KEAT. So far conditions at theses sites have 
fluctuated wildly and expect that to continue through 18z. 
Conditions will settle down around 06z...but expect fog/stratus 
to re-develop vcnty KMWH/KEAT. Tobin


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        58  36  46  32  45  42 /  90  30  10  10  20  50 
Coeur d'Alene  57  36  44  32  45  40 / 100  40  10  10  10  60 
Pullman        59  37  47  34  49  46 / 100  60  10   0  20  40 
Lewiston       62  39  51  36  52  49 /  70  60  10   0  20  20 
Colville       54  34  44  32  43  37 /  70  10  20  10  20  80 
Sandpoint      52  35  42  30  42  38 / 100  30  20  20  10  80 
Kellogg        51  34  41  31  44  41 / 100  70  30  10  10  50 
Moses Lake     62  35  50  31  44  41 /  20   0   0  10  20  50 
Wenatchee      57  36  48  33  41  35 /  20  10  10  10  40  60 
Omak           55  34  45  33  41  35 /  40  10  10  10  20  90 

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory from 11 AM this morning to 5 PM PST this afternoon 
     for Coeur d'Alene Area-Idaho Palouse. 

WA...Wind Advisory from 11 AM this morning to 5 PM PST this afternoon 
     for Spokane Area-Upper Columbia Basin-Washington Palouse. 

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