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Area forecast discussion 
National Weather Service Pocatello Idaho
650 PM MST Wednesday Dec 17 2014

Update...second update to increase the cloud cover spreading in
from the west. See previous discussion below. Huston

Updated to include potential for at least patchy dense freezing fog
tonight in the Blackfoot...Idaho Falls and Rexburg areas. Tonight is
not quite the situation we had yesterday where mixed rain and snow
fell in the evening hours where temperatures were beginning to fall.
That was also followed by some clearing of cloud cover towards
morning. Tonight some status is expected to redevelop along with
some areas that could be short on cloud cover. Idaho Falls was the
last area to clear today and just might be the best and first
location for fog to return tonight. If it turns into a status deck
100 to 200 feet off the ground...that could keep the visibility from
dropping below a quarter mile again. Have to watch this. Receiver station

Previous discussion... /issued 209 PM MST Wednesday Dec 17 2014/

Short term...a transitory high pressure ridge will be over
southeast Idaho tonight. There is still a slight chance of light
snow in the eastern Highlands and the west slopes of the central
mountains including the Stanley area. Any accumulation should be
very light. Day time Thursday the chance of snow increases with
the passage of a minor disturbance. Snow should again be limited
to the mountains with little accumulation anticipated. Fast
westerly winds off the Pacific will bring a stronger disturbance
through Friday and Friday night. This one could bring 1 to 4
inches in the mountains and up to 1 inch in the snake plain. Very
moist westerly winds looks to be developing for this weekend and
beginning Saturday this could bring potential for some significant
snow amounts to the westerly exposed higher elevations. This may
sound good for skiing...but be sure to keep current on the weather
as this could turn hazardous with some strong winds. Receiver station

Long term...Saturday night through Thursday. Active weather will
continue as we head into early next week. Moisture transport remain
strong as zonal flow sets up with the upper jet dropping into
central Idaho. Strong atmospheric river signal from the GFS arriving
in southeast Idaho by Sunday morning with moist conditions
continuing through Monday night. Snow levels lifting from 4500 feet
Sunday morning to 7500 feet by Monday morning as warm air makes its
way into the region. Models are producing around 12 to 18 inches of
snowfall over The Sawtooth range in the central mountains...and
about the same over the eastern Highlands around
Driggs/Palisades...and about a foot of new snowfall in the northern
Wasatch Range. GFS supporting a stronger boundary layer flow Sunday
night and Monday than the European model (ecmwf) and suggest better chances of
blowing snow over the mountain passes. European model (ecmwf) and GFS parallel
develop upper low over southeast Idaho on Christmas day. 00z runs
showed less amplitude on the wave coming out of the Gulf of Alaska.
Yesterdays 12z European model (ecmwf) run also showed an upper low over the region.
Still too far out to tell if this will be a significant event. A
cutoff low in the right place could make for a very white Christmas.

Aviation...dense fog lingering over kida at start of taf period.
Expect this to burn off fairly quickly heading into the early
afternoon hours...but both kpih and kida should be heading toward
LIFR conditions again tonight. This is supported by forecast
soundings and MOS guidance. Kbyi should see a period of MVFR
conditions overnight. Guidance appears to favor persistence as this
is what occurred last night. Finally at ksun...the diurnal up-valley
winds this afternoon bear watching as some stratus may advect up
that way from the snake plain. Holding to a scattered deck for now
during the afternoon hours. Hinsberger

Pih watches/warnings/advisories...


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