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Area forecast discussion 
National Weather Service Boise Idaho
851 PM MST Tuesday Nov 25 2014

Discussion...Winter Weather Advisory for snow ended at 5 PM MST for
the west central Idaho mountains and Boise Mountains...but cold
rain was still falling at McCall/Idaho at 8 PM MST suggesting snow
was still accumulating in the higher nearby mountains. Models
show precipitation shifting east tonight and Wednesday as an upper ridge
comes in from the coast. But the ridge is also expected to
flatten Thursday and Friday as an upper trough presses southward from
western Canada. As it does...temperatures will cool and the chance of snow
will increase again from north to south. Southern Idaho zones and
Oregon zones will stay mild and dry through Thursday /except for
patchy valley fog/ but the chance of rain and mountain snow will
increase in those areas Friday. On a separate topic...southwest
winds have decreased to 15-30 miles per hour in the western Magic Valley and
should stay at those speeds through the night...then decrease
to 10-15 miles per hour Wednesday. Current forecast is updates.


Aviation...MVFR-IFR conditions in rain showers at kmyl until 05z.
Otherwise VFR with scattered to broken middle-level ceilings. Patchy
valley fog expected...including the Treasure valley...but especially
in the long and round valleys and kmyl. Once fog develops expect
MVFR-IFR conditions. Surface winds tonight generally 10 knots or
less...except in the Magic Valley with southwesterly winds of 15-20
knots with gusts to near 25 knots. Winds aloft will be
northwesterly around 50 knots up through 10k feet mean sea level.


Previous discussion...
short term...tonight through Thursday...snow levels are coming
up as expected and McCall had changed over to a cold rain since
about noon. Some snowfall amounts were at the high end of the
advisory...Yellow Pine/McCall Colorado-Ops picked up 6 inches while
some other areas saw a changeover to rain and lower snow
amounts...Garden Valley picked up 2.5 inches. In the forecast /see
the new wswboi for details/...mainly expect new snow accumulation
of an inch or two north of New Meadows and up to 3 inches across
Banner Summit through the end of the day. Gusty west winds are
also building as expected across the Magic Valley where widespread
gusts of 30 to 40 miles per hour occurred since noon and local gusts around
50 miles per hour /Deer Haven/ were recorded. 12z NAM//GFS/ec and recent hrrr
runs continued the trend of a slower exit on the precipitation and
have blended those models and raised evening probability of precipitation as well. With
warming do not expect to need an extension to the Snow Advisory.
Hireswnmmwest and model blend also have more cloudiness with the
warm upper level ridge building across the intermountain northwest for
Thanksgiving day so increased sky cover and nudged highs down a
bit for the new pattern. We also should see a return of lower
Treasure valley stratus and fog /Ontario was 9 degrees colder than
Boise at 2 PM/ and fog is also possible across many areas early
Wednesday and again late Wednesday night through around noon
Thursday as warming aloft moves over moist soils.

Long term...Thursday night through pattern
setting up for the weekend as the upper ridge weakens with a
cold Canadian low pressure system and a Pacific trough converging
on the region. Temperatures will remain well above normal as the
region remains in the warm sector as well as plenty of boundary-
layer mixing. Warm front associated with Pacific trough moves
north across the area on Friday which will be the focus for rain
below 6000 feet with snow above across much of the area. Will also
see some better orographic enhancement for increased snowfall in
the west central mountains with strong southwesterly 40-50 knots 700
mb jet. By Saturday the Arctic boundary moves southward towards
the Columbia Basin. Models...outside the 12z European model (ecmwf)...remain in
good agreement keeping the boundary and coldest air stalling
out just north of the forecast area on Saturday and Sunday. 12z
European model (ecmwf) is the only exception in bringing this boundary much further
south reaching the Nevada border early Sunday. The Pacific trough off
the coast phases with a strong trough diving south out of the Gulf
of Alaska on Monday and shifts inland on Tuesday. Ahead of the
trough Sunday/Monday...southerly flow will develop for continued
warm advection for above normal temperatures. Widespread
precipitation will spread across the region Monday into Tuesday.


Boi watches/warnings/advisories...



previous short term...vm
previous long term....js/wh

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