772 
FXUS66 KOTX 262356
AFDOTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
356 PM PST Tue Feb 26 2013

.SYNOPSIS...Another quick moving, weak storm system will affect the 
region tonight and Wednesday...with yet another system due for 
Thursday. Warmer weather will make an appearance late this week, 
with spring-like temperatures expected by this weekend.

&&

.DISCUSSION...
Tonight into Wednesday...Today's brief shortwave ridging will be 
pushing off toward the east as our next weak weather system moves
onshore. Water vapor satellite imagery this afternoon shows a
weakening trough approaching western Washington and British
Columbia. Models in fairly good agreement in bringing this trough and
associated elevated front through the Inland Northwest tonight
into tomorrow. Main affects for this feature will only skirt the
region, with the Cascades, northern Washington, into the Idaho
panhandle being the best areas to receive measurable
precipitation. The models agree that this precipitation is driven
by weak warm advection and upslope affects. The moisture content
is not near as high as previous systems, so kept qpf amounts very
low. This does look like an all snow (shower) event given the
forecasted wet bulb temperatures, but amounts will be well below
advisory amounts. ty

Wednesday  Night through Saturday...The cool and unstable trough 
pattern of the past week or so will be replaced by a much warmer
more moisture laden one as strong zonal jet...currently extending
from the Gulf of Alaska to the western Pacific...begins to amplify
into a strong upper level ridge. The model solutions are all
consistent in amplifying this ridge. While ridges typically
deliver dry weather...this one will be a dirty one which means it
will bring considerable cloudiness as well as varying amounts of
precipitation. Just where the precipitation falls and how much
will occur is where this forecast becomes quite difficult. While
all the models depict some precipitation the variations are quite
remarkable considering the event is not that far into the future.

Looks like the threat of precipitation will begin late Wednesday night. 
The NAM12 is quite wet and it produces precipitation over most of
the forecast area...while the ECMWF only brings precipitation to
locations near the Cascade crest...and portions of the Idaho
Panhandle. Isentropic ascent from all the models is fairly
weak...so we will lean toward the drier EC solution. That notion
is also backed by the models containing a wet bias of late.

Precipitation chances will likely improve markedly on Thursday afternoon 
through Friday as a strong warm front moves in from the
southwest. Precipitable water levels rise from .40 inches ahead of
the front to nearly .70 inches or 170% of normal by Friday. This
moisture increase will be accompanied by strong warm air advection
and isentropic ascent which will undoubtedly produce some
precipitation. Given the prevailing S-SW flow the most significant
amounts should fall at the Cascade Crest...northern WA mountains
and Idaho Panhandle. Most of the precipitation will fall as
rain...however there will be a tricky transition period over the
northern valleys on Thursday night as the snow levels rise from
the valley floors on Thursday to nearly 6000 feet by Friday
morning. We expect the transition to be a smooth one with not much
valley snow accumulation expected before it all changes to rain. In 
the mountains we expect to see anywhere from 3 to 6 inches of 
snow...with most occurring near the Canadian border.

By late Friday night and Saturday the front will push into BC with the 
threat of precipitation waning substantially...except for
locations near the Canadian Border. 850 mb temps climb to some of
their warmest readings this winter and with ample mixing
anticipated we expect to see highs in the 50s to lower 60s. fx

Saturday night through Tuesday: The Inland Northwest will be in a 
progressive pattern, with a couple opportunities for precipitation
and moderating temperatures. A ridge of high pressure continues to
reign Saturday, but it'll be shifting east. A plume of moisture
riding over the ridge and the onshore flow will provide mostly
cloudy conditions, with the primary precipitation threat laying
near the Cascades and Canadian border. A mild southwest flow and
850mb temperatures in the lower to mid- single digits support
above normal temperatures and snow levels above 5000 feet.

Between Saturday night and Sunday a storm system comes into the
region. The cold front reaches the Cascades Saturday evening and
pushes toward Montana by Sunday morning. The supporting 500mb
shortwave trough comes on its heels. These features are relatively
sharp and the mid-level shortwave takes on a slight negative-tilt
as it moves through. Combined with the modest moisture plume this
will bring a good chance of precipitation to the region Saturday
night and Sunday morning. The exception will be in the typical
locations, including the lee of the Cascades, deeper basin and
L-C valley due to some downsloping. Chances remain high Sunday
afternoon and evening with an inverted surface trough/deformation
axis trailing into the region, before shortwave ridging develops
later Sunday night into Monday. Look for a drying trend by this
period. Cooler air comes in from the west through this period,
dropping snow levels toward 2000-3000 feet by late Sunday morning
through the afternoon, before falling toward valley floors at
night. So the precipitation that comes late Saturday into Sunday
morning should be a case of valley rain and mountain snow. However
a snow threat mixes into the valleys by late morning. Temperatures
drop closer to seasonal norms.

Between Monday night into Tuesday another systems come to the
region. Models disagree over its evolution, including how directly
it passes through the region. Regardless of this, the system
appears weaker than the Saturday night/Sunday system and does not
have the same deep moisture tap. Look for a relative increase in
precipitation chances but overall PoPs remain low. Snow levels
rise to between 2500-4000 feet. /J. Cote'


&&

.AVIATION...
00Z TAFS: A weak weather system will skirt eastern Washington and 
the ID panhandle tonight. Ceilings will lower but remain VFR at the 
TAF sites...with the best chances for light snow north of the 
KGEG-KSFF-KCOE corridor. 

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        27  42  30  43  34  48 /  10  20  10  40  50  40 
Coeur d'Alene  26  40  29  43  32  45 /  20  30  10  50  50  40 
Pullman        28  44  31  45  35  50 /   0  20  10  40  50  20 
Lewiston       31  52  35  53  38  57 /   0  10   0  30  40  20 
Colville       26  47  27  46  31  48 /  30  40  30  60  60  50 
Sandpoint      25  41  29  41  33  43 /  20  50  30  50  60  50 
Kellogg        24  39  28  43  31  44 /  20  60  30  60  60  40 
Moses Lake     29  50  30  50  34  57 /  10  10  10  40  20  10 
Wenatchee      30  50  30  49  34  54 /  20  10  10  30  20  10 
Omak           25  44  23  41  29  47 /  50  20  10  40  20  20 

&&

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

$$