Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Spokane Washington
409 am PST sun Nov 23 2014

the mountains will receive another round of accumulating snow
this afternoon and evening. The lower elevations will experience a
mix of rain and wet snow today. Monday will be a relatively quiet
and chilly day. More rain and heavy mountain snow is expected
Monday night into Tuesday. A breezy and wet weather pattern will
persist for much of the week with the mountains receiving several
rounds of snow.



Today and tonight: another round of mountain snow is on the way
for this afternoon and evening. The mountains of the Idaho
Panhandle will likely receive additional 2 to 6 inches of snow
with amounts up to 8 inches for the ridges in southern Shoshone
County favored by northwest flow. The Cascade crest will also pick
up a quick 8 to 12 inches beginning early this morning.

The system bringing precipitation today and tonight is moving
inland at this hour (230 am) into central British Columbia. As
the surface low tracks eastward today, Washington and north Idaho
will be in the warm sector leading to rising snow levels through
the day and increasing south winds. The primary forcing
mechanisms for precipitation will be warm/moist advection along a
warm front and vigorous westerly upslope flow into the Cascades
and Panhandle mountains. Despite the strong frontal forcing, the
models are in good agreement that the Lee of the Cascades into the
basin will be shadowed today due to mid-Level, Cross Cascade flow.
Places like wenathcee, Moses Lake, and Grand Coulee probably won't
see much (if any) precipitation today. The most significant
precipitation will likely occur this afternoon and early this
evening which isn't good news for folks who want to see snow
accumulate. Places like Pullman, Spokane, Coeur D'Alene, and
Davenport should see precipitation in the form of snow through
early to mid afternoon. However temperatures in the mid to upper
30s will make it difficult for snow to stick except on grassy
surfaces. Places like Sandpoint, Bonners Ferry, Priest Lake and
Metaline Falls will have a better shot of 1 to 2 inch
accumulations this afternoon.

By this evening, precipitation should be confined to the Idaho
Panhandle and the Blue Mountains. Winds in the 850-700mb layer
will veer to the northwest as this system moves into Alberta. This
wind trajectory favors the mountains of Shoshone County, high
terrain of the Camas Prairie, and Blue Mountains. Elsewhere, look
for clearing skies this evening and light winds. Areas of fog
should develop in the sheltered valleys of northeast Washington
and possibly over the Palouse, West Plains, and upper Columbia

Monday: a flat high pressure ridge on Monday should provide a
break in the active weather on Monday at least during the morning.
Another moist warm front is progged by the models to reach
southern British Columbia by Monday afternoon. There some
uncertainty with the track of this frontal system, but the
majority of eastern Washington and north Idaho should remain dry
Monday. The northern Cascades and Okanogan Highlands may
experience some light snow Monday afternoon, but the heavier
rain/snow will arrive Monday night into Tuesday. /Gkoch

Monday night through Wednesday night...larger scale ridging builds
in the vicinity of the West Coast during this time interval and
alters the storm track pattern somewhat over time. Initially the
ridging is off the coast and allows disturbances to drop down with
a northwest to southeast trajectory and dig into any moisture
streaming over the top of the amplifying ridge and steer it down
to the south and southeast. Such an occurrence is expected Monday
night into Tuesday. By late Tuesday the ridging off the coast
stops amplifying and the ridge moves west which allows the
northwest to southeast oriented storm track and jet to remain
close in proximity to the southern British Columbia border and
down into northwest Montana. The resulting close proximity of the
jet stream and potential and models hinting at various shortwaves
dropping down in the northwest flow on the east side of the narrow
ridge there is good potential for some brisk gusty winds Tuesday
and Wednesday. Since there is not much if any cold air in majority
of lowland locations for disturbances to overrun a good portion of
The Lowlands in the Lee of the Cascades and the north Idaho
Panhandle pops are likely to remain high for mountain locations to
the north but taper down to low to no pop amounts due to rain-
shadow development for most of this forecast interval. The ridging
and mixing brought about by disturbances dropping down the edges
of the ridge allow for the bulk of forecast temperatures to remain
on the warm side of what would be considered normal for this time
of year with an exception Wednesday night when a push of cold
Canadian air starts a cooling trend and lowers snow levels.

Thanksgiving Thursday through sunday: once again we are faced
with the dilemma that we have seen all week and that is continued
poor model agreement in the extended forecast. For at least the
last three nights the models have flip flopped completely for the
end of the forecast. While some consistency was present for the
12z runs and the afternoon forecast, it has all been lost with the
00z runs. So what we have been debating for the past few days was
to buy into the warmer and drier ridge pattern for the end of the
week or take the cooler one with cold polar air dropping in from
Canada. For this forecast package I went with the cooler based on
agreement from other supporting models. The Euro today was the
cooler solution and it had good support from both the Canadian and
dgex and even the 12z GFS. The warmer solution this time
encompassed the 00z and 18z GFS along with the 12z Euro. Funny
enough, just 24 hours ago this was exactly the opposite with the
majority in favor of the warmer solution.

The scenario that was incorporated into this forecast was a cold
polar front dropping in from Canada late Wednesday into
Thanksgiving Thursday bringing a good shot of precipitation with
moisture out ahead of the front. How to play pops here was very
tricky and for the most part they were left unchanged until
models better agree. This would keep the mention of precip for
most throughout the extended, but if the Euro does verify we could
expect significant drying behind the cold front. Precip on
Wednesday into Thursday could lead to some less than stellar
travel conditions for Turkey day mainly in the higher elevations
and far north, but due to low confidence I would hold off on
altering plans for now. Snow levels were lowered throughout and
are expected to reach most valley floors (minus the southern
valleys) by late Saturday as the cold air encompasses the region.
Temperatures were also trended lower to near normal by the
weekend, but will also need to be fine tuned once models better
agree. Overall we see a forecast full of uncertainties, but we
will expect better agreement once we get a little closer to this
timeframe. /Fliehman


12z tafs: a band of precipitation is expected to Blossom over
north Idaho and eastern Washington between 17-19z along a warm
front. Precipitation over much of the region will initially be in
the form of snow. Strong low level warm advection will likely lead
to a transition to rain or rain/snow mix in Pullman, Spokane, and
couer d'alene between 19z-21z. The late morning/early afternoon
development of snow should limit accumulations to grassy surfaces
with the exception of airports north of the Metro like Sandpoint,
Bonners Ferry and Colville where slushy runway accumulations up to
an inch will be possible. Dry/downslope advection from the
west/northwest this evening should disperse stratus in the
evening, but fog and low stratus may crop up toward Monday
morning. /Gkoch


Preliminary point temps/pops...
Spokane 38 27 37 32 43 38 / 90 20 10 50 60 40
Coeur D'Alene 38 28 37 33 41 39 / 100 40 10 60 80 60
Pullman 41 29 40 36 46 42 / 80 60 10 60 70 30
Lewiston 50 33 45 39 50 44 / 50 60 10 60 60 20
Colville 36 25 37 30 39 36 / 90 10 10 60 60 50
Sandpoint 36 29 37 30 39 37 / 100 40 10 70 80 80
Kellogg 35 28 35 33 38 38 / 100 80 10 70 90 70
Moses Lake 46 25 41 32 48 40 / 20 10 10 20 20 10
Wenatchee 48 29 41 34 46 41 / 10 10 10 20 30 20
Omak 37 22 37 30 41 36 / 30 10 10 30 40 50


Otx watches/warnings/advisories...
Idaho...Winter Weather Advisory until 6 am PST Monday for central
Panhandle mountains.



National Weather Service Glossary of Abbreviations