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Area forecast discussion 
National Weather Service Salt Lake City Utah
509 am MST Friday Dec 19 2014

Synopsis...high pressure aloft over Utah will yield to an
increasingly moist west to northwest flow beginning tonight. An
active period of valley rain and mountain snow will result from
this moisture over the weekend through early next week.


Short term (until 00z tuesday)...the upper ridge currently
centered over Utah will move east of the state by late this
morning. Trailing this ridge is a moist west-northwest flow which
will encompass the northern rockies/northern Great Basin tonight
through the early next week. Weak shortwaves embedded in this
prevailing flow will generate sufficient lift for fairly
widespread but mostly light precipitation through Saturday morning. The
areal extent of the precipitation should decrease a bit as heights
increase over the north Saturday afternoon/early evening.

The building ridge across the eastern Pacific this weekend will
produce downstream conditions favorable for widespread precipitation
across northern Utah beginning Saturday night and continuing into
early next week. Lift generated from strong and quite moist warm
advection will reach northern Utah Saturday evening. Looking at
widespread valley rain and snow with mountain snow developing
either late in the evening or shortly after midnight across the
far north...then spreading south and east late Saturday night
through Sunday morning. Snow levels will be on the rise late
Saturday valley areas should see rain as the
prevailing precipitation type by late Sunday morning. A series of weak
shortwaves embedded in moist northwest flow over the region should
keep organized precipitation going through Sunday night or early Monday.
Heights will begin to build over Utah as the eastern Pacific Ridge
expands further east late Sunday night/Monday. Looking at precipitation
decreasing in both areal coverage and intensity as height build
during the day Monday. Any lingering precipitation should end Monday

Have issued a Winter Storm Watch for the northern mountains
beginning late Saturday night and continuing through the day
Monday. The long duration of the event will give the expected high
density snow time to accumulate. In addition...strong near 700mb
winds developing on Sunday will serve to create hazardous travel
conditions through the higher passes. The one thing that could
impact this potential storm the most would be if the eastern
Pacific Ridge expands further east or does it more quickly this
weekend. If this does happen then the bulk of the precipitation will
remain north and east of the forecast area. The recent 00z and
06z guidance still has the focus of high qpfs over the Wasatch and
western Uinta ranges...with lesser amounts downstream over the
Wasatch Plateau. Confidence remains fairly high that a significant
winter storm will strike the northern mountains based largely in
the run-to-run consistency and general agreement amongst the
various model guidance.


Long term (after 00z tuesday)...precipitation dwindles
significantly Monday night as a building ridge plugs the moisture
tap. European model (ecmwf) suggests an influx of middle-level moisture on Tuesday so
kept chance of probability of precipitation in the northern mountains ridging flattens on
Wednesday ahead of a potent non-splitting trough Bee-lining toward

Though global models diverge on the evolution of this feature...the
recurring theme is an influx combo of cold air and moisture for
Christmas day. Precipitation should begin in earnest in the Wednesday
night/Thursday morning time frame...ushered in by very strong 700 mb
winds. Both GFS and ec show 700 mb temperatures plummeting to around
minus 15c by Thursday...enabling snow levels to likely Grace many
valley floors. Only moderate confidence thus far for amounts and
extent of precipitation across the state.


Aviation...southeast winds and ceilings above 6000 feet above ground level will continue
at the slc terminal through the morning. There is a 20 percent
chance occasional ceilings will nudge the 6k level between 12-14z.


Slc watches/warnings/advisories...
Utah...Winter Storm Watch from late Saturday night through Monday
afternoon for utz007>010.



Short term...Conger
long term/aviation...verzella

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