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Area forecast discussion 
National Weather Service Boise Idaho
851 PM MST Thursday Dec 18 2014

abundant moisture off the coast in association with the next cold
front is expected to push into eastern Oregon overnight and into
western Idaho middle morning through early afternoon. The associated
warm front moved into eastern Oregon early this evening and is now
moving into central Idaho. This will keep snow off and on in
McCall this evening. This sould be a good event for the mountain
regions with generally 3 to 6 inches of snow expected through the
end of the day Friday. This all handled well in the current
forecast. Have made a few changes to the forecast to increase
overnight temperatures slightly across the forecast area along
with increasing the winds.


Aviation...scattered MVFR snow showers will continue over the
higher terrain of southeast Oregon and the central Idaho mountains. Areas
of snow with rain below 4k feet mean sea level will spread across eastern Oregon
into the central Idaho mountains after 06z and all of southwest
Idaho after 12z with warm frontal passage. MVFR/IFR conditions with
snow...MVFR/low-VFR conditions in rain. Surface winds...south-
southeast around 10 kts. Winds aloft... southwest 15-25 kts up
through 10k feet mean sea level.

Weekend outlook...brief break in the precipitation Friday night will
be followed by widespread precipitation starting in eastern Oregon
late Saturday morning and spreading across the entire area by
Saturday evening lasting through Sunday afternoon. Snow levels 4000-
4500 feet mean sea level Saturday morning will rise to 6000-8000 feet by Saturday
afternoon/evening. Valleys will remain as all rain but will likely
see MVFR ceilings Saturday night through Sunday morning.


Previous discussion...
short term...tonight through Saturday...short wave ridge will
move through overnight...and in it/S wake we will begin the first
of two notable changes in the weather pattern impacting the
Pacific northwest. Strong moist flow will move in behind the short wave
ridge. This will begin a period of moderate to heavy precipitation that
will last into the long term. The first wave will move in Friday.
We have continued the trend of increasing probability of precipitation as confidence
increases. Precipitation will spread from west to east tonight...getting
into all of SW Idaho by tomorrow afternoon. Rainfall amounts will
range from 0.10 to 0.20 in lower elevations...with even more at
higher elevations. Temperatures will be still be above normal...but
several degrees cooler than today. Friday night we will see a
relative break in the action. On even wetter system will
begin moving into the region. Light to moderate rainfall will
move into eastern Oregon early in the day...and into SW Idaho mainly
in the afternoon. Conditions in Boise from middle afternoon into the
early evening will be cool and rainy...with temperatures in the lower
40s. Heavier precipitation will come Saturday night.

Long term...Saturday night through Tuesday...a moist flow from
the Pacific will keep our area mild wet and cloudy through Monday.
Snow levels will range from 4000 to 5000 feet Saturday evening
then rise to around 6500 feet in central Idaho and as high as 8000
feet in southeast Oregon by Sunday afternoon. Rainfall totals of
half an inch or more are expected in the valleys...falling mainly
Saturday night through Sunday evening. New snow accumulations of
12 to 18 inches are likely above 6500 feet by Monday night in the
mountains of central Idaho and Baker County Oregon. Monday night
and Tuesday an upper level ridge building north and east from
California will bring a drying trend with scattered showers
confined mainly over the mountains. Temperatures will average
around 15 degrees above normal.

Tuesday night through Thursday...the region will begin this
period in a moist northwesterly flow...but will come under the
influence of a moist/cold shortwave by Wednesday evening. This
shortwave will bring a chance of precipitation to the entire
region and will continue doing so until Christmas morning. Areas
in southeast Oregon and the Treasure valley will be the first to
dry out while higher elevations and the Magic Valley will continue
to experience a slight chance of precipitation through Christmas
night. Precipitation could come in the form of snow /including the
valleys as temperatures and snow levels drop/ by Wednesday night.
Temperatures during this period will begin about 5 degrees above
normal but will drop to normal by Thursday.


Boi watches/warnings/advisories...




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

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