Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 201250
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
550 AM MST SAT DEC 20 2014

.SYNOPSIS...A STRONG MOIST BUT MILD NORTHWEST FLOW WILL DEVELOP
ACROSS NORTHERN UTAH TONIGHT AND CONTINUE THROUGH SUNDAY NIGHT.
THE FLOW WILL BECOME COLDER AND DRIER BEHIND A COLD FRONT ON
MONDAY.

&&

.SHORT TERM (TIL 00Z WED)...THE WEAK UPPER TROF THAT CROSSED THE
CWA OVERNIGHT IS HEADING EAST BUT THERE REMAINS SUFFICIENT
MOISTURE AND INSTABILITY TO KEEP A FEW SHOWERS GOING ACROSS THE
NORTH INTO THE MORNING.

THE STRONG PAC JET WILL START NOSING INTO THE PAC NW TODAY AND
REMAIN STRONG THRU THE NRN ROCKIES JUST TO OUR NORTH THRU SUN
NIGHT. THIS SENDS COPIOUS MOISTURE INTO NRN UT WITH FAIRLY LARGE
WATER AMOUNTS EXPECTED OVER THE NRN MTNS BY MON. VERY STRONG WINDS
ARE ALSO EXPECTED ACROSS THE RIDGES.

THE AIRMASS WITH THIS MOISTURE PLUME IS FORECAST TO BECOME QUITE
MILD HOWEVER WITH SNOW LEVELS RISING TO AROUND 8000 FT BY SUNDAY
MORNING AND REMAINING THAT HIGH THRU SUN NIGHT. THIS WOULD PLACE
THE WINTER WEATHER IMPACT ABOVE MOST OF THE MAJOR PASSES THRU THE
NRN MTNS SUCH AS I-80...US-89 AND US 6. THE PASS ON US 40 IS NEAR
8000 FT AND COULD SEE A BIT MORE SNOW. THE IMPACT ABOVE THAT LEVEL
WILL BE SIGNIFICANT HOWEVER WITH HEAVY SNOW AND STRONG WINDS
CREATING HAZARDOUS TRAVEL CONDITIONS. THIS WOULD INCLUDE THE UPPER
COTTONWOOD CANYONS AND SOME OF THE HIGHER ROUTES ACROSS THE
WASATCH PLATEAU AS WELL AS RECREATION AWAY FROM DEVELOPED
HIGHWAYS.

HAVE GONE AHEAD AND UPGRADED THE EXISTING WATCH TO A WARNING ABV
7000 FT MAINLY FOR THE HIGH ELEVATION IMPACTS ALTHO SNOW WILL
START AT LOWER LEVELS TONIGHT SO THERE WILL BE MORE WIDESPREAD
IMPACT INITIALLY. HAVE LEFT OUR WYOMING ZONE WITHOUT A HIGHLIGHT
AT THIS TIME AS HERE TOO MOST PRECIP WILL END UP FALLING AS RAIN.

THE PATTERN STARTS TO AMPLIFY AND BECOMES PROGRESSIVE SUNDAY
NIGHT WITH A LOW LEVEL COLD FRONT DROPPING THRU THE CWA ON MON.
THIS SHUTS OFF THE MOISTURE FEED AND STABILIZES THE AIRMASS WITH
PRECIP TURNING MORE SHOWERY AND TAPERING OFF.

A STRONG SURFACE BUILDS S OUT OF THE NRN ROCKIES MON INTO TUE AS
THE UPPER RIDGE IN THE ERN PAC AMPLIFIES AND SHIFTS SLOWLY EAST. A
VERY STABLE AIRMASS FORMS OVER THE CWA WITH STAGNANT CONDITIONS
DEVELOPING.

&&

.LONG TERM (AFTER 00Z WEDNESDAY)...RIDGE CONTINUES TO AMPLIFY
THROUGH WEDNESDAY EVENING BEFORE FLATTENING AS A TROUGH MOVES TOWARD
UTAH FROM THE NORTHWEST. MODEL AGREEMENT OF BOTH TROUGH MOVEMENT AND
EVOLUTION HAS BEEN FAIRLY ABYSMAL...WITH 06Z GFS FURTHER WEAKENING
ITS IMPACTS. THE ECMWF DELIVERS A MUCH MORE POTENT SYSTEM WITH
EARLIER AND MORE COPIOUS PRECIPITATION ALONG WITH MUCH COLDER
TEMPERATURES...BUT FORECASTER CONSENSUS RENDERS LITTLE CONFIDENCE IN
THIS SOLUTION. PRIMARY IMPACT WILL BE A COLD FRONT CROSSING MUCH OF
THE AREA DURING CHRISTMAS DAY BRINGING SNOW TO THE MOUNTAINS AND A
CHANCE OF A MODICUM OF LOW ELEVATION SNOWFALL. MADE MINIMAL CHANGES
TO GRIDS REGARDING THIS EVENT WHILST AWAITING BETTER RUN AND MODEL
CONSISTENCY.

&&

.AVIATION...CIGS AT THE SLC TERMINAL ARE EXPECTED TO REMAIN AT OR
BELOW 6K AGL THROUGH THE MORNING...WITH PRIMARILY VFR CONDITIONS.
THERE IS A 30 PERCENT CHANCE OF MVFR CEILINGS AND A 20 PERCENT
CHANCE OF PATCHY FOG DEVELOPING BETWEEN 13-16Z. SOUTHEASTERLY TO
SOUTHERLY SURFACE WINDS ARE EXPECTED TO PREVAIL INTO THE
AFTERNOON...WITH POSSIBLE ERRATIC WINDS DURING PERIODIC VICINITY
RAIN SHOWERS.

$$

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 6 PM MST MONDAY
     FOR UTZ007>010.

WY...NONE.
&&

$$

SHORT TERM...WILENSKY
LONG TERM/AVIATION...VERZELLA

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)


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