Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 161307
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
507 AM PST Mon Jan 16 2017

.SYNOPSIS...
Dry and very chilly weather is expected into Monday. Temperatures
will begin to moderate by early next week and the dry weather
will end after that. A prolonged period of wet and warmer weather
is expected to develop by Tuesday and continue at least through
Thursday. Widespread moderate to heavy precipitation is expected
as well as appreciable snow melt over much of the area. Flooding
will be a distinct possibility by the end of next week.

&&

.DISCUSSION...


...SIGNIFICANT ICE ACCUMULATIONS POSSIBLE IN NORTH AND CENTRAL
WASHINGTON MONDAY NIGHT THROUGH TUESDAY...

...WARMER TEMPERATURES AND HEAVY RAIN MAY LEAD TO FLOODING ACROSS
EASTERN WASHINGTON AND NORTH IDAHO WEDNESDAY AND THURSDAY...

Today...The ridge of high pressure that has been over the region
the past several days will flatten and open the door for a warm
and wet weather system tonight through Thursday or so. More on
that in a second. For this morning conditions will be similar to
what we have seen over the weekend. Very chilly temperatures with
areas of fog and low clouds and light winds. Some light snow
flurries will be able to get squeezed out of the stratus through
the day. By this afternoon the area will come under the influence
of the next weather system. The upper level flow will turn to the
west and will begin to scour out the inversion. This will allow
temperatures to warm a bit over what we have seen the past several
days. There will even be a chance for some light snow near the
crest of the Cascades late this afternoon.

Tonight through Tuesday night...The well advertised wet Pacific storm
will begin to move slowly into the region tonight and Tuesday.
Each model run has been a little slower with the timing. The 00z
runs and now the incoming 06z runs have slowed the progression by
6-12 hours over what the 12z runs showed. We are still looking at
quite a wet system with PWATs over 200 percent of normal, which is
in the 99th percentile for moisture during this time of the year.
The moisture is courtesy of an Atmospheric River originally
pointed at B.C. and northwest Washington this evening. That
moisture then slides south through the state Tuesday and
Wednesday. Temperatures will be on the increase beginning this
afternoon. Temperatures will warm 10-15 degrees over the next 3
days and rise back to normal if not above normal. Highs are
expected to be in the 30s and lower 40s by Tuesday and Wednesday.

* Impacts: Nearly all areas will have the potential for mixed
  precipitation with snow/rain/freezing rain/sleet. Timing and
  accumulations will be different depending on location. But it
  now appears as if the western zones will have the best potential
  to see enough ice accumulation to warrant a winter highlight. A
  Winter Storm Watch is currently in effect. This will be
  continued and monitored closely to add or subtract forecast areas
  as we see fit. The remainder of the forecast area will see
  lesser accumulations of ice, but the effects will similar with
  treacherous driving conditions across the entire Inland
  Northwest.

* Flooding: We are looking at precipitation amounts of an inch to
  several inches from tonight through Thursday. In addition the
  water in the snow pack will be available as temperatures warm
  above freezing Tuesday afternoon. Water in the current snow pack
  ranges from 1.5-3.0 inches below 3000 feet. Add that to the QPF
  and we will have an over abundance of run-off. This will swell
  small rivers and streams. At this time we are not expecting any
  flooding on main stem rivers. The other thing we are looking at
  will be ice jam flooding as ice melts off the river and jams up
  in the channel. There is an Hydologic Outlook giving a better
  explanation and this will also be monitored. Tobin


Wednesday through Thursday: Moderate to heavy rain will continue
for most valleys across the region. Mountain snow is expected
above 3k ft across northern WA and ID. The threat of freezing rain
or sleet will continue across the Cascade valleys and across to
the Okanogan Valley as well as the Valleys of the Okanogan
Highlands and the valleys west of Colville. By the afternoon the
only freezing rain/sleet threat should be confined to the Cascade
Valleys. Wednesday Night and Thursday the threat continues for the
Cascade Valleys as well as pockets down towards highway 97 along
the Columbia River. Models do not seem to want to warm up the
surface temperatures above freezing in this region. Just the
amount of precip from Wed and Wed night is pretty significant.
Locations will see anywhere from 0.30-0.50 in the deep Columbia
Basin...around an inch for most valleys and 1 to 2 inches in the
mountains of north ID and the Cascade crest. All this
precipitation will fall in all different forms making for a messy
situation. The Wednesday commute could be difficult. Southerly
winds will continue through Thursday and remain elevated sustained
10-15 mph for much of eastern WA. Gusts 25 to 30 mph is possible
from Ritzville north and east towards Spokane and Pullman. By
Thursday afternoon we might start to dry out across portions of
the Columbia Basin and into the Spokane and Palouse region.
Surface high pressure will dominate the region ahead of another
strong low pressure system off the west coast. All this will make
for challenging impacts to our region.

*The freezing rain through Thursday will make surfaces slick and
 travel difficult across the Cascade Valleys. The potential exists
 for 0.10 or more of ice accumulation on surfaces. The rain
 falling combined with the warmer temperatures and expected wind
 will continue to erode a significant portion of our snowfall
 across much of the lowlands of central and southern WA as well as
 the southern ID Panhandle. There is a good chance of some
 flooding issues. Small streams and creeks will likely fill. Ice
 jams could be a concern as the ice starts to break up and move
 downstream. Urban flooding problems are also a concern from the
 high rain amounts combined with clogged storm drains from our
 recent snow.

Thursday Night through Friday Night: That low pressure off the
west coast will slowly move towards Vancouver Island. We will
start to see a break in the precipitation. Our best chance of snow
will be across the mountains Thursday night into Friday. Then as
the low takes a negative tilt it will bring a threat of rain/snow
to the Cascades and central WA Friday and then move north and east
through the overnight hours. Precipitation amounts look to be
significantly less than earlier in the week. Temperatures will
drop back down to near or below average for this time of the year.
/Nisbet

Saturday and Sunday: We remain under moist southwest flow as the
upper low moves north up the BC coast on Saturday, followed
closely by another potent system which moves onshore somewhere
along the WA/OR border to begin next week. Overall a showery
weekend, with the best chances in the mountains. Snow levels look
to be low enough for most to see these showers fall as snow,
outside of perhaps the lower basin where rain is possible. High
temps will be right around normal for this time of year in the low
to mid 30s. /bw


&&

.AVIATION...
12Z TAFS: The ridge of high pressure will begin to break down this
afternoon and overnight. This will allow a Pacific storm system to
move into the region tonight and Tuesday. The strong inversion of
late will linger through this evening...before beginning to
weaken over night. Persistent low clouds and fog will result in
considerable variance in ceilings and visibility for the next 24
hours. The incoming storm will will bring a a widespread mixture
of snow/freezing rain/sleet/rain to the region mainly after 12z
Tuesday. While confidence is low right now there is an outside
chance of the mixed precipitation making it to KEAT near 12z.
Tobin


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        22  20  34  34  41  33 /  10  30 100 100 100 100
Coeur d`Alene  26  21  35  32  42  33 /   0  30 100 100 100 100
Pullman        26  23  35  33  40  33 /   0  10  80 100 100 100
Lewiston       27  26  36  35  43  36 /  10  10  60 100 100  90
Colville       24  20  32  31  40  34 /  10  80  90 100 100 100
Sandpoint      26  22  34  32  42  34 /  10  60 100 100 100 100
Kellogg        28  22  33  31  41  34 /   0  20 100 100 100 100
Moses Lake     19  15  29  28  39  29 /  10  40  70  90  90  80
Wenatchee      19  15  29  27  36  28 /  10  50  60  80  80  70
Omak           26  19  32  30  39  32 /  10  50  70 100 100  90

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory until 5 PM PST this afternoon for
     Central Panhandle Mountains-Coeur d`Alene Area-Idaho
     Palouse-Lewis and Southern Nez Perce Counties-Lewiston Area-
     Northern Panhandle.

     Winter Storm Watch from this evening through Wednesday morning
     for Northern Panhandle.

WA...Air Stagnation Advisory until 5 PM PST this afternoon 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 Watch from this evening through Wednesday morning
     for East Slopes Northern Cascades-Moses Lake Area-Northeast
     Mountains-Okanogan Highlands-Okanogan Valley-Upper Columbia
     Basin-Waterville Plateau-Wenatchee Area.

&&

$$



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