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Area forecast discussion 
National Weather Service Spokane Washington
416 am PST Tuesday Dec 1 2015
low clouds with occasional flurries will be common in valleys
with a mix of sun and clouds in the mountains. A weak frontal
system will bring a wintry mix Tuesday night into
Wednesday...with an even wetter system moving in Wednesday
afternoon into early Thursday. The combination of the two weather
systems will likely produce light to moderate snow near the
Cascades and over the northern Washington mountains. There will
also be a threat of freezing rain across western portions of the
Columbia Basin, Wenatchee valley and Okanogan Valley. Wet but
warmer weather is expected from Thursday afternoon and into the


today through Wednesday...

..slick Wednesday morning commute...

A low pressure system in the Gulf of Alaska will send a short wave
trough across the region tonight into early Wednesday. Prior to
its arrival a cold air mass remains in place with a deep stratus
layer extending up to near 5000 feet mean sea level. Temperatures at the top
of the stratus layer on the 00z Spokane sounding from yesterday
were a cold -12c. This will play a role as the next system tracks
across as the cold air in place will provide added lift as a
warmer air overrides the cold air in place. The NAM model has the
best handle on the current situation with the GFS and European model (ecmwf) too
dry in the boundary layer. The NAM shows snow increasing along the
east slopes of the Cascades early this evening...reaching Omak,
Wenatchee, and Moses Lake late in the evening and then across
eastern Washington and north Idaho during the overnight hours. The
NAM shows the strongest isentropic ascent over north central
Washington with strong packing of the 850mb temps ranging from 2c
near the Tri-Cities to -9c along the east slopes of the Cascades.
This could result in a 3-5 hour period of moderate accumulating
snow and winter weather advisories will be issued. The warm tongue
aloft does reach 1-2c south of I-90 which could result in a mix of
snow and freezing rain around Othello, Lind, Pomeroy, and Lewiston
areas. The band of snow does weaken as it reaches Spokane,
Pullman, and the Idaho Panhandle as it undergoes stretching.

After this passes models are in better agreement with a break
between systems. However abundant stratus will linger into the
afternoon while the dendritic layer dries out. Models soundings
show a good chance for freezing drizzle Wednesday afternoon for
the northern valleys and Idaho Panhandle where low level
isentropic ascent and warmer advection exists with a deep stratus
layer extending up to near 6000 feet mean sea level. Due to light winds over
most of the region on Wednesday the low level air mass is expected
to only warm slightly...except on the Palouse and Lewiston area
where downslope southeast winds should provide more signicant
warming with highs in the upper 30s. Jw

Wednesday night through Sunday...

*second storm will bring freezing rain and more snow to locations
that will receive snow with the first storm*

The previous storm is just a precursor to what will be a very
active 5 days (or more). Southwesterly flow aloft will become
established over the region as a deep trough builds off the Pacific northwest
coast. This will allow a significant plume of moisture to reach
the inland northwest shooting precipitable water values up to .75
to .90. Not 1.00+ like what the entire Pacific northwest coast will be
seeing...but a marked increase nonetheless.

Moisture moves in from the south and west during the evening
hours. The initial forecast challenge will be how much cold air
remains trapped at the surface as warm air aloft shoots over the
Columbia Basin and wateville plateau. NAM, GFS, and European model (ecmwf) all
paint a very similar picture with 850 temps between 0 and 2 deg c
reaching the entire Douglas County and portions of Grant County
while surface temps remain below freezing. This would indicate at
least a period of freezing rain or sleet during the onset of the
precipitation Wednesday night. Given the initial snowfall totals,
we will be separating these two events. Shortly after the initial
advisory expires, we will need to consider adding another advisory
to address the freezing rain and valley snow in many of the same
locations that will receive snow Tuesday night.

By Thursday afternoon, warm air will finally reach the surface in
most areas around the inland northwest. A few lingering rain/snow
showers mainly over the mountains through Friday. Then another
very moist system moves into the Pacific northwest bringing valley rain and
mountain snow to the region through the weekend. It doesn't end
there with another system hot on its heals set to arrive early
next week. After a relatively dry October/November, looks like
December will bring back a very active weather pattern for at
least the first week.


12z tafs: no significant changes to the ongoing forecast. Made
minor adjustments to the ceilings based on current trends. No vis
restrictions due to snow or fog although a few radar echoes
showing up near kmwh as a weak short wave moves across the region.
Will watch this closely as this could reach kgeg in the next
couple of hours.

Otherwise the challenge remains to be how much stratus will break
up today ahead of our first good chance of snow in about a week.
Improved ceilings this afternoon at all locations before bringing
them back down overnight as the precip arrives. Hinted at snow in
the last 6 hours of the taf at keat, kmwh, and kgeg. This also
includes the chance of freezing rain at keat early Wednesday
morning. /Ab


Preliminary point temps/pops...
Spokane 27 25 32 32 42 34 / 10 50 90 50 30 50
Coeur D'Alene 27 25 32 32 45 36 / 0 20 90 40 40 50
Pullman 33 27 38 38 45 36 / 10 20 70 30 30 60
Lewiston 35 28 38 38 49 39 / 10 20 50 30 20 40
Colville 24 22 31 31 40 33 / 10 80 80 70 70 60
Sandpoint 27 22 30 30 41 35 / 0 20 90 40 50 60
Kellogg 25 23 31 30 42 34 / 0 10 80 30 20 60
Moses Lake 25 25 31 31 41 33 / 10 100 40 70 40 30
Wenatchee 26 24 30 30 38 32 / 10 100 40 100 50 40
Omak 25 24 30 30 38 31 / 10 100 40 100 70 50


Otx watches/warnings/advisories...
Idaho...air stagnation advisory until noon PST Friday for central
Panhandle mountains-Coeur D'Alene area-Idaho Palouse-Lewis
and southern Nez Perce counties-Lewiston area-northern

Washington...air stagnation advisory until noon PST Friday for east slopes
northern Cascades-lower Garfield and Asotin counties-Moses
Lake area-northeast Blue Mountains-northeast mountains-
Okanogan Highlands-Okanogan Valley-Spokane area-upper
Columbia Basin-Washington Palouse-Waterville Plateau-
Wenatchee area.

Winter Weather Advisory from 10 PM this evening to 7 am PST
Wednesday for Moses Lake area-Okanogan Highlands-Okanogan
Valley-upper Columbia Basin-Waterville Plateau-Wenatchee

Winter Weather Advisory from 7 PM this evening to 7 am PST
Wednesday for east slopes northern Cascades.



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