Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 252245
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
345 PM MST THU DEC 25 2014

.SYNOPSIS...THE UPPER LEVEL LOW PRESSURE SYSTEM OVER WESTERN UTAH
WILL SETTLE INTO THE FOUR CORNERS REGION EARLY FRIDAY...THEN EXIT
THE REGION FRIDAY NIGHT. A NEW ROUND OF UNSETTLED WEATHER WILL
DEVELOP LATE IN THE WEEKEND AND REMAIN THROUGH THE FIRST HALF OF
THE NEW WEEK.


&&

.SHORT TERM (UNTIL 00Z SUNDAY)...THE UPPER LOW SLIDING SOUTH
THROUGH WESTERN UTAH THIS AFTERNOON WILL EVENTUALLY TURN EAST AND
SETTLE INTO THE FOUR CORNERS REGION BY EARLY FRIDAY. WIDESPREAD
LIGHT TO LOCALLY MODERATE SNOW PERSISTS IN THE WRAP AROUND WARM
ADVECTION IN THE NORTH AND WEST FLANKS OF THE LOW LATE THIS
AFTERNOON. ACCUMULATING SNOWS ARE EXPECTED TO REMAIN FAIRLY CLOSE
TO THE LOW CENTER OVERNIGHT. LOOKING AT HEAVIER SNOWS TO RETURN
TO CENTRAL AND SOUTHERN UTAH LATER THIS EVENING AS THE LOW CENTER
MOVES INTO EXTREME SOUTHERN UTAH. NORTHERN UTAH WILL SEE SNOW
DECREASE IN AREAL COVERAGE AND INTENSITY DURING THE EVENING AS A
BACKDOOR COLD FRONT MOVES WEST OUT OF SOUTHWEST WYOMING AND BRINGS
MORE STABLE AIR AND DOWNSLOPE CONDITIONS TO NORTHERN UTAH.

HAVE LEFT ALL OF THE WARNINGS/ADVISORIES IN PLACE WITH THE
AFTERNOON FORECAST PACKAGE. EXPECT THAT THE VARIOUS HIGHLIGHTS
ACROSS NORTHERN UTAH WILL BE DROPPED OVERNIGHT AS THE SNOW AND
WINDS GRADUALLY DISSIPATE. SOUTHERN AND CENTRAL UTAH WILL LIKELY
SEE ACCUMULATING SNOWS CONTINUE ALONG THE I-15 CORRIDOR AND OVER
THE HIGHER TERRAIN IN CLOSE PROXIMITY TO THE UPPER LOW.

THE ANTI-CYCLONIC NORTHERLY FLOW TRAILING THE EXITING FORE CORNERS
LOW FRIDAY NIGHT WILL BRING AN END TO ANY LINGERING SNOW BY EARLY
FRIDAY EVENING. VERY COLD TEMPS ARE EXPECTED AS CLOUD COVER
DIMINISHES AND WINDS DECREASE. SOME FOG COULD DEVELOP BY SATURDAY
MORNING...THOUGH AT THIS TIME THE AREAL COVERAGE LOOKS TO BE
LIMITED.

THE SHORTWAVE RIDGE MOVING SOUTHEAST ACROSS THE GREAT BASIN
SATURDAY WILL MAINTAIN DRY CONDITIONS WITH TEMPS INCREASING A BIT
COMPARED TO FRIDAY. ANY INCREASE IN TEMPS LOOKS TO BE MINOR DUE TO
EXTENSIVE SNOW COVER AND GENERALLY STABLE CONDITIONS.

&&

.LONG TERM (AFTER 00Z SUNDAY)...GLOBAL MODELS CONTINUE TO REMAIN IN
QUITE GOOD AGREEMENT REGARDING THE BIG PICTURE EVOLUTION OF THE NEXT
AND VERY COLD TROUGH LATE WEEKEND INTO EARLY NEXT WEEK. RAPID
AMPLIFICATION OF THE WEST COAST RIDGE WILL ALLOW A SHORT WAVE TO
CARVE SOUTH THROUGH THE GREAT BASIN SATURDAY NIGHT SETTING UP A
BROAD LONG WAVE TROUGH ACROSS MUCH OF THE WESTERN CONUS THROUGH THAT
TIME. THE AIRMASS ASSOCIATED REMAINS CONTINENTAL...QUITE DRY AND
VERY COLD WITH H7 TEMPS DROPPING INTO THE -15 TO -17 C RANGE MONDAY
THROUGH TUESDAY.

THE NOSE OF A 100KT CYCLONIC JET WILL PUSH INTO NORTHERN UTAH SUNDAY
NIGHT...COINCIDENT WITH MODEST NEAR H7 BAROCLINICITY PUSHING IN FROM
THE NORTH...THIS ASSOCIATED WITH THE STRONGEST PERIOD OF COLD
ADVECTION LATE SATURDAY NIGHT INTO SUNDAY. CONTINUE TO HOLD ONTO
LIKELY MOUNTAIN POPS AND HIGH CHANCE VALLEY POPS ACROSS THE NORTHERN
HALF OF THE FORECAST AREA AS SAID FORCING SHOULD PRODUCE A BROAD
AREA OF LIGHT SNOW AND OR SNOW SHOWERS. HIGH SNOW RATIOS AND VERY
COLD TEMPS IN PLACE COULD ALLOW EVEN VERY LIGHT SNOWFALL TO STICK TO
ROADWAYS...BUT THOSE IMPACTS WILL NEED TO BE LOOKED AT CLOSER AS THE
EVENT NEARS.

12Z GUIDANCE IN BETTER AGREEMENT WITH THE UPPER TROUGH EVOLUTION
THEREAFTER THROUGH THE REMAINDER OF THE LONG TERM PERIOD AS WELL.
BOTH THE GFS/ECMWF SHOW THE UPPER TROUGH CUTTING OFF FROM THE
NORTHERN BRANCH AND SPINNING UP OVER CENTRAL CALIFORNIA TUESDAY
NIGHT INTO WEDNESDAY...BEFORE SLOWLY TRANSITIONING EAST ACROSS
NORTHERN AZ LATE WEEK. POPS IN GRIDS OVER THIS PERIOD DECREASE IN
VALUES WITH AREAL EXTENT FOLLOWING THE MID LEVEL DEFORMATION SOUTH
ACROSS THE FORECAST AREA DURING THE MIDWEEK PERIOD WHERE THE BEST
LIFT WOULD OCCUR. GEFS ENSEMBLE MEAN TIES CLOSELY W/THE OPERATIONAL
IDEAS AND IF THESE TRENDS CONTINUE COULD SEE BUMPING POPS UP ACROSS
THE FAR SOUTH DAY 5 ON.

MODELS STILL PORTRAYING DECENT EASTERN FLOW COUPLED W/CAA ACROSS THE
NORTHERN WASATCH/FRONT TUESDAY...BUT ORIENTATION OF UPPER LOW OVER
CENTRAL CALIFORNIA NOT IDEAL TO GENERATE MUCH MORE THAT MODERATE
DOWNSLOPE POTENTIAL. WILL CONTINUE TO MONITOR THIS AS MODELS WILL
LIKELY SHIFT IN PLACEMENT A BIT.

&&

.AVIATION...IFR CONDITIONS IN LIGHT SNOW ARE EXPECTED TO PERSIST AT
TIMES THROUGH THROUGH 02-03Z BEFORE IMPROVEMENT IS REALIZED. THROUGH
THAT TIME UP TO 1 INCH OF ACCUMULATION CAN BE EXPECTED ON NON
TREATED SURFACES ACROSS THE AIRFIELD. LIGHT NORTHERLY WINDS ARE
EXPECTED TO CONTINUE THROUGH THE NIGHT...WITH A 40 PERCENT CHANCE OF
BECOMING LIGHT AND VARIABLE BY MIDNIGHT...AND A THEN LIGHT
SOUTHEASTERLY AFTER 10Z. CIGS ARE EXPECTED TO REMAIN BELOW 6000FT
AGL INTO TOMORROW MORNING.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING UNTIL NOON MST FRIDAY FOR UTZ001>004-
     006>010-014>016-517-518.

     WINTER WEATHER ADVISORY UNTIL NOON MST FRIDAY FOR UTZ005.

WY...WINTER STORM WARNING UNTIL NOON MST FRIDAY FOR WYZ021.

&&

$$

SHORT TERM...CONGER
LONG TERM/AVIATION...MERRILL

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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