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Area forecast discussion 
National Weather Service Spokane Washington
429 am PST Tuesday Jan 27 2015

Synopsis...
areas of low clouds and fog will persist across portions of
inland northwest as high pressure remains in place. A couple of
weak storm systems will affect the area Tuesday through Thursday
and bring a small chance of showers and cooler temperatures to the
region. A ridge of high pressure will then rebound late in the
week for drier weather and more fog, before breaking down next
weekend. The next best threat of precipitation, including possible
rain and snow, arrives Sunday.

&&

Discussion...

Today through Wed: the main challenges for today and Wed will be
similar to the last few days, namely fog and/or the areal
coverage of stratus...as well as pcpn chances. Much of ern WA
and north Idaho remain under a canopy of low clouds and areas of fog.
Concerning the dense fog advisory...we expect vsbys to waver
considerably due to mid clouds aloft altering radiative cooling.
The upper ridge will break down fully as a quick moving short-wave
trough crosses the region by later today...with an accompanying
cold front that will move through by Wed morning. Towns close to
the Cascades and in the nrn WA valleys likely won't mix completely
and could remain under fog and/or low clouds a good part of the
day. Given the deep dry lyr above the moist surface, the best
chance of rain will be in the Cascades and mountains of north Idaho
tonight through Wed. Pcpn amnts should be light with snow levels
likely not falling below 4000 feet. Bz

Wednesday night to saturday: the inland northwest will be dominated by a
dirty ridge, with mostly dry conditions and a continuing patchy
fog threat. The dry conditions will be interrupted by two
shortwaves, with localized shower chances.

Shortwave (1) comes between Wednesday night and Thursday as a
small-scale vorticity Max moves across the region. This will be
going on even as the long-wave ridge is rebounding, hence the
term: dirty ridge. Agreement on the precise track of that
vorticity Max is only fair. Loose agreement tracks it by southern
Washington and the lower Panhandle. Pwats in its path linger are depicted
between 0.30-0.50 inches (which is around 100-130% of normal).
Models even show some minor instability here too. So this will
bring some deeper clouds and slight shower chances across The
Blues/Camas Prairie and central Panhandle mountains. A few models
bring showers to the higher Palouse/l-c valley, as well as farther
west near the mountains of southern Chelan County. There is enough
model agreement to add slight chances to these areas. Elsewhere
conditions will be mostly dry, but look for low clouds around the
Columbia Basin and Mountain Valley. I cannot rule out stray
sprinkles or drizzle coming out of the low clouds where they are
thick enough, but confidence in that detail is low. Snow levels
average between 3 to 5kft, lowest in the Lee of the Cascades and
northern mountains and highest over southeast Washington to the lower
Panhandle.

Shortwave (2) comes between Friday and Saturday when a system
enters northern British Columbia and slides southeast to skim by northeast Washington
and Idaho. The brunt of the system, at this point, appears to track
east of the Idaho/Montana border. Still this will bring the next threat of
precipitation to the NE Washington and Idaho Panhandle mountains for Friday
night and Saturday. Behind that shortwave dry, cooler air comes
in. Pwats drop back to between 0.10 to 0.20 inches and snow levels
drop back toward 2-4kft. Average temperatures drop closer to
seasonal averages. /J. Cote'

Saturday night to monday: a more organized system pushes into the
region, with the next good chance of precipitation, which may
include rain and snow. The leading warm front lifts into the
region Saturday night into Sunday with strengthening isentropic
ascent, deepening moisture (with pwats rising to between 0.35 and
0.65 inches by sunday) and expanding precipitation chances. There
is some disagreement on how quickly the precipitation develops
with the warm front. Some start it overnight and others holds it
off until Sunday morning. Confidence leans toward the later time,
given model trends and time needed to saturate the atmosphere
again. Overall the best lift and precipitation threat comes Sunday
afternoon and evening when models bring the first mid-level trough
into the region and flatten the ridge. So pops are highest this
time frame.

Then between Sunday night and Monday models veer in somewhat
opposite directions. Shortwave systems continue to satellite
broader trough in the Gulf of Alaska. Yet depending on which model run
you look at they either track the systems north toward Alaska/British Columbia or
east into Washington. The easterly tracking solutions keep the region
wetter. There is some favor given to the wetter solution. Yet
overall with the developing westerly flow the highest pops threat
by this time will favor the highest pops in the mountains by this
time frame.

Snow levels will be near 2-4kt and overnight lows in many areas
will be near to below freezing again. This will favor any
potential precipitation as snow or a rain/snow mix during the
night and morning hours, with valley rain and mountain snow in the
afternoon hours. Early indications suggest several inches of snow
are possible in the mountains, but not certain given model
disagreements. /J. Cote'



&&

Aviation...
12z tafs: a ridge aloft will keep a lid on the moist boundary
layer the next 8-12 hrs. This is still a low confidence forecast
regarding timing and duration of vsby restrictions. A pair of
weak waves will converge over the region and weaken the ridge this
evening. Low clouds and fog will impact Wenatchee and Moses Lake
with additional development expected vcnty of Spokane- cd'a.
Pullman and Lewiston will maintain light southeast flow and remain
generally VFR. Confidence is incr that boundary layer winds will
switch around to the west/SW tomorrow which is favorable for
advecting low clouds in central Washington eastward toward the Washington/Idaho
border. This would swing the probabilities for restrictions back
to kgeg-kcoe-kpuw and potential clearing for keat-kmwh.

&&

Preliminary point temps/pops...
Spokane 45 31 41 33 41 31 / 0 0 0 10 10 0
Coeur D'Alene 47 33 41 32 42 30 / 0 10 10 10 10 10
Pullman 52 37 49 35 46 34 / 0 10 10 20 10 0
Lewiston 56 39 54 37 50 35 / 0 10 10 10 10 0
Colville 39 30 38 30 38 27 / 0 0 0 0 0 0
Sandpoint 40 30 40 30 40 29 / 0 10 10 10 10 10
Kellogg 44 33 42 31 42 30 / 0 10 10 10 10 10
Moses Lake 42 32 41 32 43 31 / 0 0 0 0 0 0
Wenatchee 38 33 41 32 41 32 / 0 0 0 10 0 0
Omak 36 31 37 28 38 28 / 0 0 0 0 0 0

&&

Otx watches/warnings/advisories...
Idaho...dense fog advisory until noon PST today for northern Panhandle.

Washington...dense fog advisory until noon PST today for Moses Lake area-
northeast mountains-Okanogan Highlands-upper Columbia Basin.

&&

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