Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Spokane Washington
242 am PST Friday Dec 26 2014

Synopsis...
a vigorous low pressure system will produce widespread
accumulating snow Saturday into Sunday. The heaviest snow
amounts will likely occur over the Idaho Panhandle where amounts
of 5 to 9 inches will be a good bet by Sunday morning. Bitterly
cold northeast winds will develop by Monday morning. Temperatures
will be well below average most of next week as Arctic high
pressure settles over the inland northwest.



&&

..winter storm to bring heavy snow to the Idaho Panhandle and
moderate accumulations to portions of eastern Washington this
weekend...

Today and tonight: a weak upper level disturbance will exit the
southern Idaho Panhandle this morning in the northerly flow. Look
for snow accumulations of an inch or less in the mountains of
southern Shoshone County and around Winchester/Craigmont mainly
before sunrise. Low clouds and fog will fill the sheltered valleys
of northeast Washington and north Idaho again this morning. With
very little wind expected today, low clouds and fog may be slow to
dissipate around Colville, Cusick, the Spokane river, and over
Lake Roosevelt. A good deal of sunshine is expected again today
over the Columbia Basin and east slopes of the Cascades.
Temperatures exceeded all guidance yesterday at Wenatchee, Omak
and Moses Lake. It may be tough to have a repeat of the mid to
upper 40s again today, but it will be another relatively mild and
mainly sunny day for these areas. /Gkoch

Saturday through Sunday night...models continue to show an upper
low dropping out of British Columbia into the inland northwest
this weekend. During the bulk of the dynamics with this
system...strong mid level westerly flow will be present favoring
heavy snow accumulations for the Cascade crest and Idaho
Panhandle. However strong mid level forcing and favorable jet
support will favor moderate accumulations for much of eastern
Washington as well. Northwest upslope flow into the Blue Mountains
and Camas Prairie will also yield significant snow accumulations.
During the initial event on Saturday...moist isentropic ascent
will overtake areas mainly east of a line from Republic to
Ritzville with widespread light to moderate precip developing.
Then Saturday night into Sunday morning the upper low drops
southeast into northeast Washington and north Idaho. The potential
remains for a deformation zone to set up which could result in a
band of heavier snowfall like the 06z NAM and 00z uw WRF-GFS show.
The models are beginning to come into line (except the 00z GFS
which is further south) of the low tracking from near Kelowna, British Columbia
southeast towards Sandpoint with this band of heavier precip
possibly developing somewhere between Ione to Deer Park stretching
east between Bonners Ferry and Coeur D'Alene. Confidence is low
with its precise location and intensity. On Sunday afternoon into
Sunday night the cold upper trough lingers, although dynamic lift
diminishes. This in combination with increasing north-NE winds
bringing in colder and drier air from the northeast by Sunday
night will lead to a gradual decrease in snow showers.

*Snow levels: most areas will see just snow through this event.
Although a tongue of warmer air will sneak into areas from
Ritzville to Pullman south with snow levels rising to near 2500
feet Saturday afternoon. However snow levels will fall again down
to the valley floors overnight Saturday night as cooler air moves
back into these areas.

*Snow amounts: periods of snow will occur over a prolonged 36 hour
duration. The heaviest accumulations will be in the central
Panhandle mountains with 10-15 inches expected with the highest 2
day snow totals in the mountains. The north Idaho Panhandle,
Coeur D'Alene area, and Idaho Palouse will see 2 day snow totals
of 5-10 inches. The northeast Washington mountains, Spokane area,
and Washington Palouse will see 3-6 inches with the highest
amounts near the Idaho border. The Blue Mountains and Camas
Prairie may pick up 7-11 inches. Across the Columbia Basin and
Lewiston area amounts are expected to be light...generally around
an inch for Lewiston with little to no accumulation for the
Wenatchee area, and Moses Lake area. Strong westerly flow will
also favor only light snow amounts away from the Cascade crest
including plain, Leavenworth, and Winthrop.

*Winds: as the low moves into northeast Washington into the north
Idaho Panhandle Saturday night breezy winds will develop south of
the low, especially on the Palouse. This will lead to areas of
blowing snow mainly above 3000 feet (blue mountains, locally on
the Camas Prairie and central Panhandle mountains). High
temperatures on the Palouse in the low to mid 30s is expected to
limit blowing snow potential.

*Hazards: confidence remains high of snow creating hazardous
travel conditions in the Idaho Panhandle. Snow will also lead to
difficult travel over the Cascade Mountain passes, and over
portions of eastern Washington especially near the Idaho border.
/Jw

Monday through thursday: the wind and cold temperatures on Monday
will produce cold wind chills. Northeast winds have been increased
Monday with sustained winds of 10 to 20 mph with gusts to 30 mph
common over much of the inland northwest. Stiff cold advection
and the likelihood of fresh snow cover over north Idaho and much
of eastern Washington suggest that temperatures won't warm much
through the day on Monday. Temperatures should remain well below
average most of next week. There should be an abundance of
sunshine Tuesday and filtered sunshine (through high clouds)
Wednesday. However, temperatures will struggle to climb into the
teens and low 20s Tuesday and Wednesday afternoon. /Gkoch

&&

Aviation...
06z tafs: a pair of weak circulations diving down the Idaho/Washington border
will keep a small threat for isolated snow showers from Spokane to
Pullman to Lewiston through 11z. A quick burst of snow could bring
a few tenths of accumulations with a low water content. Drier
northerly flow will come in the wake of this wave but similar to
last night, it appears to weaken as the morning progresses and
confidence is low whether stratus and fog will redevelop at
locations like kpuw/ksff/kgeg/kcoe. MOS and BUFKIT data varies
and adds increased uncertainty. /Sb




&&

Preliminary point temps/pops...
Spokane 34 25 32 27 31 18 / 0 20 100 90 60 40
Coeur D'Alene 33 24 31 27 31 17 / 10 20 100 100 60 40
Pullman 35 25 33 28 30 15 / 30 10 100 90 80 50
Lewiston 39 26 37 32 36 24 / 40 10 50 90 70 50
Colville 33 23 32 25 32 19 / 0 20 90 90 50 30
Sandpoint 32 24 31 26 31 17 / 0 30 100 100 60 20
Kellogg 31 23 30 25 30 15 / 20 20 100 100 80 40
Moses Lake 41 24 36 26 36 25 / 0 10 40 20 20 20
Wenatchee 41 25 39 26 35 26 / 0 10 20 30 10 30
Omak 35 22 30 23 30 20 / 0 10 20 50 30 30

&&

Otx watches/warnings/advisories...
Idaho...Winter Storm Watch from late tonight through Sunday morning for
central Panhandle mountains-Coeur D'Alene area-Idaho
Palouse-northern Panhandle.

Washington...none.
&&

$$

National Weather Service Glossary of Abbreviations