636 
FXUS66 KOTX 041023
AFDOTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
223 AM PST Fri Jan 4 2013

.SYNOPSIS... 
A weak disturbance will bring occasional flurries or light snow to
most of the region this morning. The weather pattern will become
more active through the next week under a more moist and
progressive flow pattern. Snow levels will increase through early
next week with valleys transitioning from snow over to rain or a
wintry mix. The milder temperatures will last into mid week before
a cold front drops temperatures back down closer to seasonal
normals.

&&

.DISCUSSION...
Today through Saturday...The strong upper level ridge which has
bedeviled the region for the last week is being flattened this
morning by a rather weak upper level short wave. Satellite...radar
and surface observations suggest nothing much is reaching the
surface other than on mountain slopes from the weak dynamic
support and mid level frontal lift associated with this feeble
disturbance. Still...the wave will allow a weakening of the mid
level subsidence inversion today...but not much effect on the low
level inversion...and charge the boundary layer air mass with
some more moisture to promote a return of widespread valley and
basin low clouds over the next 24 to 36 hours as the ridge builds
back this afternoon through tonight. In the deep basin and Cascade
valleys the inversion layer is deeper and latest model soundings
from Omak to Wenatchee still depict a supercooled moisture sodden boundary
layer which will bring a threat of light freezing drizzle in
addition to the snow flurries possible over the rest of the low
lands north of interstate 90 today and tonight. All in all today
will be fairly quiet with perhaps a dusting of fresh snow over the
northern tier zones and generally cloudy and continued cool
conditions elsewhere.

Tonight will be typically cool but not as cold as previous nights
owing to the high likelihood of widespread low stratus decks
curtailing radiational cooling potential in the basin and valley
zones. On Saturday an increasingly meridional trough will
approach the region off the Pacific...shove the rebuilt ridge axis
eastward and allow the arrival of the next significant synoptic
weather system over the cascades and western basin zones by
afternoon. Light snow onset is likely west of a Moses lake and
Republic line during the afternoon....while the eastern half of
the forecast area will experience a dry but cloudy and continued
seasonably cool day. /Fugazzi

Saturday night through Wednesday: The Inland Northwest remains in
an active west-northwest flow with a series of shortwaves moving
in from the Pacific. Since yesterday model agreement and
consistency has degraded regarding the evolution of the
shortwaves. However loose agreement continues to show a system
moving through Saturday night into Sunday, with a second passing
sometime between Monday and Wednesday morning. Confidence in the
details has declined.

The differences begin with the first system. Some guidance has
trended wetter and slowed its exit. Others have remained more
progressive and generates less precipitation. This is largely a
factor of when and how much the system stretches and/or splits on
its way inland. Either way there will be increasing snow shower
chances Saturday night and Sunday, before starting to wane Sunday
night. The highest confidence for measurable precipitation remains
in the mountain zones. However I did increase precipitation
chances for Saturday evening through Sunday, including some brief
periods of likely PoPs outside of the mountains. This is a nod to
the fact all but the ECMWF indicates some measurable precipitation.
This could result in up to an inch or two of snow in the valleys,
less in the Basin and areas under 2000 feet, and locally higher
amounts in the mountains. At this point snowfall amounts do not
look high enough to warrant any highlights and given the continue
model uncertainty, the potential for any highlights would be held
off either way.

Between Monday and Wednesday a broader trough migrates inland.
Prior runs indicated modest agreement in a leading warm front
coming in through Monday afternoon and Monday night, with an
accompanying cold front passing Tuesday or Tuesday night. More
recent runs diverge. The more progressive guidance brings a
leading warm front and renewed precipitation to the region early
Monday, with a second reinforcing wave Monday night into Tuesday
before a cold front sags through Tuesday night into Wednesday
morning. Other guidance brings the leading warm front and renewed
precipitation chances Monday night into Tuesday morning, with the
second reinforcing wave coming in Tuesday afternoon with cold
front passage Tuesday night into Wednesday morning. So at this
point the largest disagreement comes on Monday. However regardless
of timing a moist west-northwest flow will keep higher than normal
precipitation chances across the eastern third of Washington and
northern Idaho. More confident precipitation chances comes Monday
night through Tuesday night, before the precipitation becomes more
showery and focus shifts into the mountain zones Wednesday into
Thursday, until the general threat starts to increase again late
Thursday as the next wave approaches.

Great uncertainty exists with regard the precipitation-type,
largely tied to when snow levels rise. The more progressive
solutions raise snow levels on Monday, while others hold them
closer to valley/basin floors until Tuesday morning or afternoon.
The forecast will include the potential for snow, along with some
rain, through Monday night in most areas, before a general valley
rain/mountain snow threat comes Tuesday. There are still
indications for freezing rain late Monday night into Tuesday,
especially over the Basin through the lee of the Cascades where a
southeast flow will be more likely to promote cold-air damming
while milder air surges in aloft. Some pockets of freezing rain
will be possible across the northeast Washington and Idaho
Panhandle mountain valleys Tuesday night, before the cold front
passages transitions much of the region to an general snow shower
threat again by Wednesday. /J. Cote'

Wednesday through Thursday Night: Large scale trof over the NW
part of the country will continue to push cooler air into the
region. This period will feature a continued active pattern for the
Inland NW...but the flow will have limited moisture decreasing
the chance for any significant valley snowfall but higher
elevations could see a decent shot at snow. Winds Wednesday for
mainly the basin and higher elevations will be breezy but no
impacts are expected.

Beginning the period on Wednesday a shortwave trof embedded in the
larger scale system will have snow likely in the Cascades. This
feature will also have an early wave of moisture exiting the WA
Palouse and ID Panhandle that will have brought light snow to
these areas. With continued NW flow through the remainder of the
period looks like the majority of the associated moisture will
remain on the windward side of the Cascades allowing the Crests to
likely obtain a decent amount of snowfall. Moisture that does make
it across the Cascades will have the best chance of precipitating
once again in the Central ID Panhandle Mtns and Blue Mtns. Total QPF
for the period looks to be rather insignificant for our area so
currently don't anticipate many impacts but the forecast will
continue to get refined in the coming days to get a better idea of
some snowfall expectations.

Temperatures will continue to be on the decline from the warm up
we saw earlier in the week with highs near or a little below
average and low temps near average. These temps should allow snow
levels to remain at valley floors for most areas minus the L-C valley
and deep Basin areas that may see some flakes given sufficient moisture
during the cooler overnight hours. /Fliehman

&&

.AVIATION...
06Z TAFs: low clouds and fog to become problematic again in many
aviation locations along with a disturbance passing over which
could produce light snow flurries in addition to light freezing
drizzle overnight and into Friday morning. Ceilings and
visibilities mostly in the MVFR category due to all of this
weather phenomena. /Pelatti

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        27  21  32  25  32  25 /  10   0  10  60  50  20 
Coeur d'Alene  28  22  32  25  33  27 /  10  10  10  50  60  30 
Pullman        30  23  33  26  34  26 /  10   0  10  40  60  20 
Lewiston       35  28  39  31  40  32 /  10   0  10  20  40  20 
Colville       30  24  32  27  34  26 /  20  10  20  60  50  30 
Sandpoint      27  23  31  27  31  28 /  20  10  10  40  60  30 
Kellogg        29  22  34  25  31  26 /  30  10  10  40  50  40 
Moses Lake     28  24  32  26  30  26 /  10   0  30  60  30  20 
Wenatchee      27  24  30  25  31  26 /  10  10  50  70  30  20 
Omak           26  22  28  25  29  23 /  10   0  50  60  30  20 

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$