Area Forecast Discussion
Issued by NWS Spokane, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KOTX 222237
AFDOTX

AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
237 PM PST MON DEC 22 2014

.SYNOPSIS...
Expect dry conditions with areas of fog tonight and early Tuesday.
Light mountain snow and valley rain or snow will return late
Tuesday. An organized storm system will impact the region around
Christmas Eve. This will bring the potential for moderate to heavy
snow in the mountains and light accumulations to the valleys.
Another storm will impact the region next weekend.

&&

.DISCUSSION...

Tonight and Tuesday: As of 2pm, the majority of the snow showers
over the Central and Southern Idaho Panhandle have exited south
and east of our area. Fog and stratus has continued to decrease
through the morning and early afternoon hours with only some
stubborn fog remaining in the northeastern valleys of Washington
encompassing Chewelah, Colville and Northport among others. Slow
dissipations will continue through the remaining afternoon hours
before redevelopment is expected this evening into the overnight
hours.

For tonight we will continue to see a ridge of high pressure move
over the area that will allow for calm and stable conditions
to set up. With sufficient low level moisture coupled with light
winds and cooling temperatures, low stratus and fog is expected
to develop. Much of the region is anticipated to see fog and/or
stratus with the Palouse being the only higher confidence area to
remain clear due to the downsloping off the terrain to the SE.

Tuesday will bring the front edge of our next approaching storm
system with it reaching the Cascades early Tuesday before
spreading east into northern Washington midday. Snow levels drop
to near valleys floors for the east slopes and northern WA valleys
by this point allowing for almost all precip to fall as snow.
Throughout Tuesday the majority of the precipitation will remain
confined to the Cascades with only lighter amounts outside of this
area. Snow totals through Tuesday afternoon will generally sit in
the 3 to 8 inch range for the higher Cascades with 2 to 5 inches
possible at Stevens Pass. This could lead to some slick conditions
over the pass. Other areas will generally receive under an inch
through the day. This period merely serves as the introduction for the
complex weather present through the middle of the week. /Fliehman

...MODERATE THREAT FOR SNOW TO IMPACT MOUNTAIN PASSES WEDNESDAY...
...LIGHTER ACCUMULATIONS POSSIBLE IN THE VALLEYS OF NORTHERN IDAHO...

Tuesday night through Thursday: A moist storm system will pass through
the region during this time-frame bringing mountain snows, a mix
of valley rain/snow, and return to more seasonal temperatures.
Confidence is increasing with this system as the GFS is now better
aligned with the NAM/SREF/EC. Consequently, a trof of low pressure
dropping out of the Gulf of AK will shove a rich, narrow plume of
moisture across the Canadian Border Tuesday night then southward
through the remainder of Ern WA/Nrn ID through the day
Wednesday...finally departing Thursday morning with drier and
cooler conditions settling in. Light to moderate precipitation
will accompany the passing moisture plume and largely fall as
mountain snow and valley rain with a few exceptions. The first is
the potential for the air mass to remain cool enough in the
valleys adjacent to the Canadian Border (Bonners Ferry, Metaline
Falls, Laurier) and second being cooler air bleeding into the
region on the backside of the steady precipitation bringing a
switch from rain to snow which also introduces the possibility to
a period of light valley snow before all said and done. The later
scenario does not typically support accumulations because valley
temperatures rarely cool enough even after the switch over and
there is always the possibility that precipitation ends too quick.

* Snow: Most mountain locations will receive some snow. The
  heaviest mountain snow look to be along the Cascade Crest and
  Idaho Panhandle where 6-12 inches will be possible. For the
  Cascades, this will start above pass levels Tuesday evening then
  fall to pass levels overnight which will reduce pass level
  accumulations significantly. Confidence is moderate to high but
  actual snow levels at pass levels will fluctuate some so
  particular accumulations between 4-5K feet carry moderate to low
  confidence.

Northern Valleys: a few inches of snow will be possible in the
valleys of northeastern WA and Northern ID including Bonners
Ferry, Sandpoint, Metaline Falls, and Ione. Thermal profiles that
set up Tuesday afternoon will be critical for expected amounts and
if these locations change to rain Wednesday morning. Model
guidance indicates ranges from less than an inch to up to five
inches. QPF amounts definitely support this but thermal profiles
carry low confidence.

Southeast: 2-4 inches will be possible in the Blue Mtns, Camas Prairie,
and benches surrounding the Central Panhandle Mtns of ID Wednesday
night into Thursday morning following the transition from rain to
snow. This includes locations like Anatone, Winchester, Nez Perce,
Deary, and Santa to name a few. Confidence is higher for the Camas
Prairie and Blue Mtns than Central Panhandle Mtn area.

Valleys below 3000 feet: (except near immediate Canadian Border) Trace
to 1.5 inches possible east of a line from Republic to Pomeroy
with snow chances arriving Wednesday afternoon as rain switches to
snow. Confidence for any particular amount is very low due to
temperatures remaining above freezing. Slightly better chances
will be for communities above 2000 feet. This includes Northern
Idaho, Spokane-CDA Area, Palouse, and Lewiston Area.

* Mountain Passes: Snow is likely to impact mountain passes alongI-90,
  Hwy 2, and Hwy 20 starting Tuesday night and continue through
  Wednesday. For additional travel information: click the Seasonal
  Links over the map on our home page or visit the WA or ID DOT
  sites.

I-90:
Snoqualmie: will start off as rain Tuesday evening but should
switch to snow by early Wednesday morning. Amounts look to be
light.

Lookout Pass: will start off as snow Tuesday night, may briefly mix
with rain or become heavy wet snow overnight, then become all
snow for Wednesday. Moderate to heavy amounts are possible.

Hwy 2:
Stevens Pass: will be a mix of rain/snow or rain Tuesday evening
but should quickly switch over to snow overnight and remain snow
on Wednesday. Amounts look to be light.

Hwy 20:
Sherman Pass: Snow Tuesday night into Wednesday morning then
tapering off through the day. Amounts will look to be light

Christmas Night and Friday: An upper level ridge temporarily
builds into the Pac NW for generally decreasing chance of
precipitation. The best chance of precip will reside over the
central and southern ID Panhandle. Temperatures will be around
average for this time of the year.

Saturday through Sunday: Another upper level trough will move
into the Pac NW bringing a round of mainly snow to the area. There
are some pretty big differences in the GFS and EC with this
potential winter weather event. The GFS is quicker in bringing the
trough towards the west coast and breaking down the ridge. GFS
shows it crossing the Cascades by Saturday morning. Meanwhile the
ECMWF has it off the WA coast during that time. The EC also takes
the bulk of the energy to the south of our area. Both models do
show a surface low moving through...the GFS takes it right through
Spokane...the EC has it closer to the WA/OR border. The main
changes made to the forecast was increased chance of precipitation
quite a bit starting Friday night and continuing through Sunday.
The bulk of the precip looks to fall Saturday though. Temps look
to be tricky Saturday as southerly flow will bring warmer air into
portions of the Columbia Basin. How far that warm air goes will
make or break our chance of snow for Spokane. Currently going 33
for a high in Spokane. Think the west plains will see snow with
the lower elevations of downtown Spokane and out towards the
valley will see rain/snow mix. All valleys north of Spokane should
see snow. The rain/snow area will be Wenatchee into Moses Lake,
Ritzville and La Crosse. By Sunday night the low shifts south or
east and our flow turns more northerly. This will usher in cooler
temperatures as well as drier air. Sunday generally chance of
precip will be wanning as drier air approaches.

Monday: The drier air arrives and dries us out. Have decreased
chance of precip so that only mention of snow is across the
southern corner of Shoshone Co and in the Camas Prairie. The drier
air brings clearing skies. That also means good radiational
cooling during the night and trying to recover during the day.
Have trended temperatures down. Temps Sunday night into Monday
will be about 2-8 degrees below average for this time of the year.
The colder temps will be across extreme eastern WA and north
ID...with just slightly below average temps across Central WA.
Monday high temps will be about 2-9 degrees below average. Monday
night into Tuesday temps have the potential to be even colder...
/Nisbet

&&

.AVIATION...
18Z TAFS: VFR conditions expected at all TAF sites through 06Z
Tuesday as high pressure builds over the region. After 06Z the
main forecast issue will be the possible formation of IFR or low
MVFR stratus under a strengthening inversion over the Columbia
basin and KGEG vcnty TAF sites...but an increase in mid level
clouds overnight may limit inversion strength and lessen the
chance of any significant stratus. This forecast element is low
confidence at this time with a general  continued VFR forecast
the safest bet fro Tuesday morning. /MJF

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        28  38  34  38  26  34 /   0  10  60  90  30  10
Coeur d`Alene  28  38  33  37  26  34 /   0  10  80  90  40  10
Pullman        29  41  34  40  29  35 /   0  10  20 100  70  10
Lewiston       32  43  37  43  32  38 /   0  10  10 100  80  10
Colville       26  36  30  35  25  32 /  10  30  70  50  10  10
Sandpoint      27  35  30  35  27  32 /  10  20 100  90  40  10
Kellogg        27  35  33  35  29  31 /   0  20  80 100  90  30
Moses Lake     30  40  35  39  28  38 /   0  10  10  70  10  10
Wenatchee      31  40  34  39  29  36 /   0  20  10  50  10  10
Omak           27  36  30  36  25  31 /   0  30  30  20  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Watch from Tuesday evening through Wednesday
     afternoon for Northern Panhandle.

     Winter Storm Watch from Tuesday evening through Thursday morning
     for Central Panhandle Mountains.

WA...None.
&&




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.