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Area forecast discussion 
National Weather Service Boise Idaho
1004 am MST Sat Dec 3 2016

Discussion...low to mid clouds today as a weak warm front
transitions across the region. Temperatures will reach the low
40s in the lower valleys and low to mid 30s in the mountain
valleys. Expecting light snow showers over the mountains north of
a Burns-Ontario-Fairfield line with this disturbance, diminishing
this afternoon. Accumulations expected to be about an inch or
less. Northwest flow aloft will combine with a deep moisture
plume tonight, bringing more significant snow accumulations to the
mountains tonight and light snow showers elsewhere. A Winter
Weather Advisory is now in affect for the west central and Boise
mountain for the period in which we expect the highest
accumulation rates to occur, between 5 am MST and 11 PM MST
Sunday. However, light snow showers will continue after this time
period for a few more hours over the mountains. Will be looking
closely at the Weiser River Valley and Boise Metro today for
potential impacts with this system as the Weiser River Valley is
close to advisory level criteria and the Boise Metro may see a
brief period of light snow as the cold front transitions through
the area just in time for the Monday morning commute. Current
forecast is on track. No updates this morning.


Aviation...MVFR ceilings in mountains this morning will lift to low
VFR this afternoon and any isolated snow showers will dissipate.
Lower valleys will see VFR ceilings through the day. Surface winds
10-15 kts out of the west-northwest today with northwest winds 20-30
kts at 10k feet mean sea level.

Tonight and sunday: IFR conditions and snow develop after 06z in
east-central Oregon and west-central Idaho mountains. Sites above
4500 feet will see IFR in snow on Sunday with widespread mountain
obscuration. Lower sites could start as snow Sunday morning, but
will likely change to rain by 18z. Surface winds are 10-20 kts
across open terrain with the strongest winds across southeast Oregon
on Sunday. Will see west winds of 40-50 kts at 10k feet.


Previous discussion...
short through Sunday night...a warm front will pass
over the region today, bringing clouds to most areas and a few
showers to the mountains. This is the forerunner to a strong
storm system that will bring heavy snow to the mountains Sunday
into Sunday night. The Winter Storm Watch has been changed to a
Winter Weather Advisory, indicating increased confidence in the
occurrence of a significant event. Ahead of the system, we will
see mostly cloudy skies today as temperatures reach near normal.
Snow showers will increase in the mountains, but snowfall totals
today will be an inch or less. Tonight, moisture will increase in
northwest flow aloft, and snow will increase further after
midnight. Amounts will initially be light, but by around 6 am MST,
snowfall will really start to pick up. Heavy snow will last
through the day and into the evening, with amounts averaging 5 to
9 inches between 5000 and 7000 feet, and 9 to 13 inches above 7000
feet. One area not in the advisory that will be closely monitored
is the upper Weiser river basin. The forecast is for the main
roadways to see mostly rain until late Sunday. Therefore that area
was not included in the advisory. However, it is a close call and
a change in the snow level of a few hundred feet could result in
snow-covered roadways and hazardous travel. Another area of
potential impact is Baker County. The mountains will see plenty of
snow, but at this time we are only forecasting about an inch in
Baker City and along the Interstate, so again no advisory has been
issued for that area.

The heaviest snow will fall Sunday afternoon into Sunday evening
as a strong cold front moves through. The timing of the front will
allow temperatures to reach near normal Sunday afternoon. Lift
from the front will enhance the ongoing snowfall. Snowfall rates
of an inch per hour will occur on northwest-facing slopes above
7000 feet. Wind gusts will briefly reach 20 mph in the lower
elevations, and up to 35 mph in the mountains as and shortly after
the front moves through. Snow will taper off after roughly
midnight, and the advisory is currently set to end at 11 PM MST.
Light snow will continue through the night, with additional
accumulations expected to be less than one inch. The cold front
will usher in the coldest air of the season to date. Lows Monday
morning will be 5 to 15 degrees colder than Sunday morning.

Long term...Monday through Friday...Monday will be partly cloudy
and cooler. An upper level trough originating over Alaska will
bring colder air and scattered snow showers Monday night and
Tuesday. Temperatures will be around 10 degrees below normal by
Wednesday. A warm front will spread snow showers across the area
Thursday and Thursday night, and scattered snow showers will
continue through Saturday, as temperatures moderate to near normal
under westerly flow aloft.


Boi watches/warnings/advisories...
Idaho...Winter Weather Advisory from 5 am to 11 PM MST Sunday idz011-013.




previous short term...snow pellets
previous long term....jt

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