Strong Wind in Washington, October 16, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
436 AM PDT Tue Oct 16 2012

.SYNOPSIS...Windy conditions with scattered rain and high mountain
snow showers will affect the region today. Wind gusts of 35 to 50 mph
will be likely through this evening over portions of the Inland
Northwest. A drier, more stable pattern is expected for Wednesday
and Thursday, before more precipitation chances enter late in the
week with cooler temperatures.

&&

.DISCUSSION...

...VERY WINDY CONDITIONS TODAY...

Today and tonight...The cold front continues to move southeast
across the forecast area this morning with the back edge just south
of the I-90 corridor as of 08Z. The main area of steady rain is
confined to Shoshone county but widely scattered showers are
popping up all across the area in the unstable post frontal air
mass. A few lightning strikes have been recorded across the extreme
northern Cascades and across southern BC. The cold pool aloft will
keep things unsettled enough for a slight chance of thunderstorms
through about 15Z before the best forcing moves east. Gusty winds
are starting to increase as the surface pressure gradient
strengthens between the deepening low over southern Alberta and high
pressure off the coast. The gradient is expected to max out late
this morning to early afternoon. The benchmark that will support a
high wind warning is at least a 24mb difference between Lethbridge,
Alberta (CYQL) and Yakima (KYKM) along with synoptic support from a
jet streak overhead. We will be just shy of the gradient and the jet
will sag to the south this afternoon. This likely means that we will
be seeing a high end wind advisory. There could possibly be one or
two of the windier sites breaking into high wind criteria but
widespread damaging winds are not expected with this system. It will
also be a fast mover, with the low sliding into the Canadian
Prairies by 00z, weakening the gradient. No changes made to the
ongoing wind advisory at this time.

Another concern will be snow levels for the east slopes of the
Cascades. Models are bringing the 850mb 0C line along the crest with
the NAM12 down to -1C this morning. Radar mosaic is showing some
evidence of a convergent zone. The HRRR model agrees, but shows the
plume drifting south along the crest into slightly warmer air.
Depending on the location and persistence of this feature, some of
the higher valleys could see some light snowfall accumulation. After
a relatively mild morning, due to strong mixing by gusty winds,
temperatures will not warm very much today as cold air advection
takes over. Expect chilly temperatures tonight with most of the
northern valleys dipping below the freezing mark. For other valley
locations, mid 30s will be common. /Kelch

Wednesday through Thursday...Latest models are in good agreement
for this period. A quite break will grace the region as a weak
but perceptible short wave ridge builds over the forecast area in
the wake of Tuesday's unpleasantness. Residual breezy winds and
lingering showers over the Idaho Panhandle will decrease Wednesday
morning as surface high pressure settles over the region. Wednesday's
highs will peak right around seasonal normal with generally partly
cloudy to mostly sunny skies. The quiet break will continue on
Thursday although the ridge axis will pass to the east of the
region and open the way for increasing high clouds as the next
weather system approaches. The retreat of the ridge axis will
allow some warm advection to begin on Thursday in the pre-frontal
southwest flow regime...promoting high temperatures once again
slightly above normal...but with sunshine filtered through
thickening clouds especially across the northern zones.

Thursday night and Friday...The GFS and ECMWF models advertise a
ridge breakdown and subsequent cold front passage either Thursday
night (GFS) or Friday (EC). Both models have stuck to their
respective timing differences over the last few runs. The driving
force of a 120-140kt jet over the Gulf Of Alaska associated with
this wave suggest the faster GFS may be the best solution to work
with. Forecast will be based upon this reasoning...which yields
high pops over much of the forecast area Thursday night and into
Friday morning as a strong fetch of precipitable water enhances
along the cold front with good and well defined jet divergence and
differential PVA. High temperatures Friday are low
confidence...with the current forecast reflecting an assumption
of a morning precipitation threat followed by good afternoon
adiabatic mixing promoting high temperatures above average...but
if the EC is correct then highs may top out closer to average. In
any event...after the relatively benign conditions of Wednesday
and Thursday...there is high confidence that Friday will bring a
change to this pattern.

Friday night through Monday...Things get rather messy and
uncertain during this period with respect to timing multiple minor
waves and fronts in a much more progressive...cooler and wet
pattern. Where certainty is higher is the overall pattern
reflected by all the latest models featuring a cool zonal or
moderately cold troffy flow regime with the storm track to the
south of the forecast area. This argues for a broad brush approach
featuring a chance of valley rain and mountain snow each day
through the weekend and early next week...with the added
possibility of some overnight non-accumulating snow flakes down
to the valley and basin floors if any particular disturbance rides
through during the overnight or early morning hours. The deep
basin in the lee of the Cascades will probably miss out on any
significant precipitation given the rain shadow promoting mean
westerly flow. During this period the mountains above 4000 to 5000 feet
are likely to receive their first significant snow
accumulations...slowly building up to three to seven inches
through the weekend. Thus...confidence is high for a raw...breezy
and occasionally wet regime during this period...although
confidence is low regarding timing of any of the expected
transient focusing mechanisms and fronts. /Fugazzi

&&

.AVIATION...
12Z TAFS: The upper level trough has moved over the region this
morning with scattered thunderstorms across the panhandle of
Idaho. Convection has moved east of most terminals, except KLWS.
A line of storms will affect extreme southeast WA and the central
panhandle through about 15z. Moist upslope flow into KGEG, KSFF, KCOE
and at KPUW will result in some low stratus before drier air aloft
begins to clear skies out and improve conditions. Winds are beginning
to gust out of the west and southwest and will intensify by 18Z
with gusts to of 35 to 40 kts common.  Scattered showers will
affect the Idaho panhandle through this afternoon, then diminish.
Winds will start to slacken by 01Z then become light after 06Z. As
winds become light, low stratus may form at any and all terminals.
/EK

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        56  37  54  37  60  43 /  30  10   0   0  10  60
Coeur d'Alene  55  34  53  33  60  40 /  50  10   0   0  10  60
Pullman        57  31  53  36  62  42 /  70  10   0   0  10  60
Lewiston       63  39  58  40  68  47 /  70  10   0   0  10  50
Colville       60  29  57  34  60  36 /  30  10  10   0  10  60
Sandpoint      53  33  52  32  57  39 /  70  10  10   0  10  60
Kellogg        50  35  48  32  56  39 /  90  20  10   0  10  70
Moses Lake     62  34  60  37  64  42 /  10   0   0   0  10  20
Wenatchee      58  40  57  39  65  45 /  10   0   0   0  10  30
Omak           61  33  59  37  62  38 /  10   0   0  10  10  60

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory until 8 PM PDT this evening for Coeur d'Alene Area-
     Idaho Palouse-Lewiston Area.

WA...Wind Advisory until 8 PM PDT this evening for Lower Garfield and
     Asotin Counties-Moses Lake Area-Spokane Area-Upper Columbia
     Basin-Washington Palouse-Waterville Plateau-Wenatchee Area.

&&