Weather Service Report


782 
FXUS66 KOTX 171237
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
437 AM PST Tue Jan 17 2017

.SYNOPSIS...
A prolonged period of active weather develops Today and continues
at least through Thursday. This will start out as a wintry mix, 
with the potential for significant snow or ice for some, before 
transitioning to warmer, wet weather later Wednesday into 
Thursday. Localized flooding will also be possibility.


&&

.DISCUSSION...

...SIGNIFICANT ICE ACCUMULATIONS POSSIBLE IN CENTRAL AND NORTHERN WASHINGTON... 
...WARMER TEMPERATURES AND HEAVY RAIN MAY LEAD TO LOCALIZED FLOODING ACROSS
   EASTERN WASHINGTON AND NORTH IDAHO WEDNESDAY AND THURSDAY...

Today through Thursday morning...The well advertised pattern change
is underway this morning. Satellite loopers show the ridge 
beginning to get flattened as the a low pressure system moves into
the eastern Pacific. This upper level low will come through the 
region in several waves. The first is the weakest and will move 
through the region today. The second will move through the region 
tonight and Wednesday. And the main trough will move through the 
region likely on Thursday. Each of these waves will have a warm 
front associated with it, which will provide the main lifting 
process, at least for the first two. Currently the deepest 
moisture is pointed at Southern B.C. So the precipitation amounts 
today will not be as much as previously expected. There likely 
will be a break in the precipitation late this afternoon. Then the
next wave will move in from the southwest this evening. This wave
will have a better/deeper moisture tap and will result in much 
higher precipitation amounts. Temperatures will make a rebound 
rebound today with highs in the 20s and even warmer on Wednesday 
with high creeping above normal.

Precipitation type and amounts: For early this morning there will
be areas in the basin and along the east slopes that will have 
flurries and localized light freezing drizzle falling out of the 
stratus, with light snow near the Cascade crest. Otherwise, a dome
of cold air currently resides of the Inland Northwest. As this 
warm, moist over-running air moves over that dome this morning we 
will see a mixture of snow/freezing rain/sleet. Amounts will be 
pretty light except for for the Cascades and lower east slopes. 
Tonight the second wave will move into the region and begin to 
erode the cold air from the top to the bottom. This will increase 
the chances for freezing precipitation across the region. And 
finally by Wednesday afternoon the dome of cold air will just 
about be gone and precipitation should be as low elevation rain 
and mountain snow. The exception will be along the east slopes of 
the Cascades and the Methow valley where the cold air will have a 
much tougher time mixing out. 

Impacts: The next 24-36 hours are going to be a bit messy. Surfaces
will become ice coated and result in hazardous driving 
conditions, broken tree limbs and possible issues with power 
lines. Numerous winter Weather Highlights are in place starting 
this morning to cover the on set of the light freezing 
precipitation, but the heavier precipitation and thus the biggest 
challenges will be tonight into Wednesday morning. Tobin

Thursday through Saturday: The upper level trough will push
through the region Thursday. This will give extreme eastern WA and
north ID one more round of moderate rainfall amounts...mainly in
the morning. Meanwhile across the Cascade valleys surface temps
will still remain below freezing with a warm nose aloft. Have put
in a slight chance of freezing rain through the day and into the
evening. It isn't until the late afternoon or evening when the
cold front passes that the temperatures profile goes below zero
for just snow. By this point the heaviest precip in the Cascades
is over and we are really talking about very little ice
accumulation potential. Meanwhile in the Columbia Basin the chance
of precipitation will decrease through the day. Thursday night 
into Friday morning the next low pressure system will move closer 
to the coastline and take a negative tilt approach and bring a 
wave in from south. Models agree on the best threat of snow with 
this wave will be across the Cascades and into the Waterville 
Plateau and Okanogan Valley and Highlands Friday and Friday night.
Easterly flow into the mountains will produce good upslope flow 
into areas that many times do not receive precipitation. In fact,
the heaviest snow accumulations on Friday could be east of the 
Cascade crest, such as the higher benches around Highway 97 west 
towards Leavenworth and Lucerne. Friday night through Saturday 
kept a chance of rain or snow for the rest of the forecast area as
that wave moves through. However it looks to shear and break 
apart as it moves through. So the amount of precip we would see 
should be light. Daytime temps will start out slightly above 
average Thursday and then trend down towards near or below average
by Saturday. Min temps will be at or below average once again. 
/Nisbet

Saturday night through Monday: Another wave rotates around the 
offshore low over our area during the day on Sunday. We remain 
under moist southwest flow as the parent low ejects inland on 
Monday. This means a generally wet and unsettled weekend into 
next week. Most of the region will see snow showers, with a 
rain/snow mix or even just rain possible for the lower Basin
at times during the day. The exact timing and placement of this 
precip is uncertain at the moment as models disagree greatly on 
the exact track of the low as it moves inland, anywhere from 
southern BC to southern Oregon. /bw 

&&

.AVIATION...
12Z TAFS: The inversion will begin to break down today as a Pacific
weather system moves into the region. Prevailing VFR cigs/vsby 
may drop down to MVFR/IFR briefly through 15z as the inversion
breaks down...but that will be short lived. A bigger concern will
be the chance for frozen and freezing precipitation the next 
24-36 hours. This weather system will come in several waves...the
first wave today will be the weakest and will bring a chance for 
a hundredth or two of Snow/freezing rain/sleet... but confidence 
in any measurable precipitation is low through 00z. That will 
change from 00-12z where all TAF sites will likely record 
measurable -FZRA/-IP. Accumulations of ice will range from
0.24-0.39 for KEAT/KMWH 00-12z. A trace at KLWS to 0.10 at
KPUW/KCOE/KSFF/KGEG between 00-06z Wednesday. Temperatures are 
expected to warm rapidly above freezing across the eastern TAF
sites. The exception will be KEAT and possibly KMWH. Tobin

&&

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

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory until 10 AM PST this morning for Central 
     Panhandle Mountains-Coeur d'Alene Area-Idaho Palouse-Lewis 
     and Southern Nez Perce Counties-Lewiston Area-Northern 
     Panhandle. 

     Winter Storm Warning from 7 AM this morning to 8 AM PST Thursday 
     for Northern Panhandle. 

     Freezing Rain Advisory from 9 AM this morning to 4 PM PST this 
     afternoon for Central Panhandle Mountains-Coeur d'Alene 
     Area-Idaho Palouse. 

WA...Air Stagnation Advisory until 10 AM PST this morning for East 
     Slopes Northern Cascades-Lower Garfield and Asotin Counties-
     Moses Lake Area-Northeast Blue Mountains-Northeast 
     Mountains-Okanogan Highlands-Okanogan Valley-Spokane Area-
     Upper Columbia Basin-Washington Palouse-Waterville Plateau-
     Wenatchee Area. 

     Winter Storm Warning from 7 AM this morning to 8 AM PST Thursday 
     for East Slopes Northern Cascades-Northeast Mountains-
     Okanogan Highlands-Okanogan Valley. 

     Freezing Rain Advisory from 9 AM this morning to 4 PM PST this 
     afternoon for Spokane Area-Washington Palouse. 

     Freezing Rain Advisory from 9 AM this morning to 8 AM PST 
     Wednesday for Upper Columbia Basin. 

     Ice Storm Warning from 7 AM this morning to 9 AM PST Wednesday 
     for Moses Lake Area. 

     Ice Storm Warning from 7 AM this morning to 4 PM PST Wednesday 
     for East Slopes Northern Cascades-Waterville Plateau-
     Wenatchee Area. 

&&

$$

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Western Regional Climate Center, wrcc@dri.edu