Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 232244
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
344 PM MST TUE DEC 23 2014

.SYNOPSIS...HIGH PRESSURE WILL BUILD OVER THE AREA THROUGH TONIGHT.
THE HIGH SHIFTS EAST WEDNESDAY AHEAD OF A COLD WINTER STORM FOR
CHRISTMAS DAY AND FRIDAY. UNSETTLED WEATHER WILL CONTINUE INTO THE
WEEKEND AND EARLY NEXT WEEK.

&&

.SHORT TERM (THROUGH 00Z SATURDAY)...HIGH PRESSURE IN PLACE OVER
THE FORECAST AREA THIS AFTERNOON...RESULTING IN DRY AND STABLE
CONDITIONS WITH MOSTLY CLEAR SKIES. LIMITED MIXING IS KEEPING
TEMPERATURES DOWN DESPITE A WARMING AIRMASS...BUT EVEN SO MAXES
ARE STILL RUNNING RIGHT AROUND SEASONAL NORMS.

HIGH PRESSURE WILL CONTINUE TO BUILD THROUGH EARLY TOMORROW BEFORE
THE RIDGE AXIS SLIDES EAST AHEAD OF THE NEXT APPROACHING WINTER
STORM. SOUTHWESTERLY FLOW WILL PICK UP...ALLOWING FOR IMPROVED
MIXING. AS A RESULT...MAXES WILL TEND TO RUN AT LEAST 5F ABOVE
VALUES OBSERVED TODAY...EXCEPT OVER EASTERN UTAH WHERE CONDITIONS
WILL STAY MORE STABLE.

NOT MUCH CHANGE IN THE 12Z GUIDANCE WITH REGARD TO THE CHRISTMAS
STORM SYSTEM. THE SYSTEM NOSES INTO NORTHWEST UTAH LATE
WEDNESDAY...WITH THE FRONT MAKING ITS WAY THROUGH MUCH OF THE
STATE THURSDAY MORNING. SNOW LEVELS SHOULD DROP TO VALLEY FLOORS
SOON AFTER PRECIP BEGINS...AND THE GREATEST BURST OF SNOW SHOULD
BE WITH THE FRONT ON THURSDAY MORNING. COLD POOL INSTABILITY WILL
KEEP SNOW GOING THROUGH THE AFTERNOON ON THURSDAY. THE STORM SLOWS
DOWN AND SPLITS A BIT OVER THE AREA THURSDAY NIGHT/FRIDAY...WHICH
WILL KEEP SOME SNOW GOING...AT LEAST OVER THE HIGHER TERRAIN OF
NORTHERN AND CENTRAL UTAH. DID NOT CHANGE VALLEY/MOUNTAIN VALLEY
SNOW AMOUNTS MUCH WITH THE AFTERNOON PACKAGE BUT DID LOWER
NORTHERN MOUNTAIN TOTALS A BIT. AM CONCERNED THAT LACK OF FLOW
BEHIND THE FRONT WILL LIMIT THE OROGRAPHIC COMPONENT. GOING WINTER
STORM WATCHES COVER THE THREAT WELL AT THIS TIME.

&&

.LONG TERM (AFTER 00Z SATURDAY)...MOISTURE LINGERS FRIDAY
EVENING AS THE TROUGH LAGS IN EXITING THE STATE. A TRAILING
SHORTWAVE PROMPTLY DIVES SOUTH THROUGH THE AREA...REINFORCING THE
TROUGH AND OFFERING A CHANCE OF ADDITIONAL PRECIPITATION IN NORTHERN
UTAH FRIDAY NIGHT INTO SATURDAY MORNING. SATURDAY AFTERNOON BRINGS A
BREAK IN THE ACTION BEFORE ANOTHER DISTURBANCE SLUMPS TOWARD UTAH
SATURDAY NIGHT INTO SUNDAY.

MODELS DIFFER SIGNIFICANTLY ON THE NATURE OF THIS FEATURE...WITH THE
GFS SENDING MOST OF THE ENERGY NORTH OF THE AREA AND LEAVING A
SMATTERING OF PRECIP GRAZING NORTHERN UTAH. THE ECMWF IS MUCH MORE
CONFIDENT IN DISPLAYING THIS FEATURE AS A DEEPENING TROUGH SPREADING
ITS MOISTURE AND 500 MB COLD POOL NEARLY TO THE SOUTHEASTERN REACHES
OF THE CWA. HAVE NUDGED POPS TO CLIMO FOR THIS PERIOD TO ACCOMMODATE
THIS DISCREPANCY.

700MB TEMPS ARE WIDELY DISPARATE AS WELL...WITH THE GFS SPIRALING
UPWARDS WHILE THE EC PLUMMETS. THUS LITTLE CHANGE MADE TO TEMP GRIDS
UNTIL FURTHER MODEL AGREEMENT IS REACHED. BIGGEST IMPACT FOR A TEMP
DIFFERENCE WOULD BE FOR P-TYPE AT THE LOWEST ELEVATIONS. HIGHEST
CONFIDENCE FOR THIS LONG-TERM PERIOD IS THE PERSISTENCE OF SUB-CLIMO
TEMPS STATEWIDE.

&&

.AVIATION...NORTHERLY WINDS WILL SWITCH TO SOUTHEAST AROUND 03-04Z
AS PER NORM.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WATCH FROM LATE WEDNESDAY NIGHT THROUGH FRIDAY
     MORNING FOR UTZ001>010-014>016-517-518.

WY...WINTER STORM WATCH FROM LATE WEDNESDAY NIGHT THROUGH FRIDAY
     MORNING FOR WYZ021.

&&

$$

SHORT TERM...TRAPHAGAN
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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