Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 191209
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
509 AM MST FRI 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 PRECIP THROUGH SATURDAY MORNING. THE
AREAL EXTENT OF THE PRECIP 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 PRECIP
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 NIGHT...SO VALLEY AREAS SHOULD SEE RAIN AS THE
PREVAILING PRECIP TYPE BY LATE SUNDAY MORNING. A SERIES OF WEAK
SHORTWAVES EMBEDDED IN MOIST NORTHWEST FLOW OVER THE REGION SHOULD
KEEP ORGANIZED PRECIP 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 PRECIP
DECREASING IN BOTH AREAL COVERAGE AND INTENSITY AS HEIGHT BUILD
DURING THE DAY MONDAY. ANY LINGERING PRECIP SHOULD END MONDAY
NIGHT.

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 PRECIP 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. ECMWF SUGGESTS AN INFLUX OF MID-LEVEL MOISTURE ON TUESDAY SO
KEPT CHANCE OF POPS IN THE NORTHERN MTNS. RIDGING FLATTENS ON
WEDNESDAY AHEAD OF A POTENT NON-SPLITTING TROUGH BEE-LINING TOWARD
UTAH.

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. PRECIP 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 TEMPS 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 PRECIP ACROSS THE STATE.

&&

.AVIATION...SOUTHEAST WINDS AND CIGS ABOVE 6000 FT AGL WILL CONTINUE
AT THE SLC TERMINAL THROUGH THE MORNING. THERE IS A 20 PERCENT
CHANCE OCCASIONAL CIGS WILL NUDGE THE 6K LEVEL BETWEEN 12-14Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY
     AFTERNOON FOR UTZ007>010.

WY...NONE.
&&

$$

SHORT TERM...CONGER
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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