Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 221252
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
552 AM MST MON DEC 22 2014

.SYNOPSIS...A VERY MOIST AND STRONG NORTHWEST FLOW WILL CONTINUE
ACROSS NORTHERN AND CENTRAL UTAH TODAY. THE FLOW WILL BECOME MORE
NORTHERLY AND DRIER TONIGHT. HIGH PRESSURE WILL BUILD INTO THE
AREA TUESDAY INTO WEDNESDAY.

&&

.SHORT TERM (THRU 00Z THU)...THE STRONG MOIST NORTHWEST FLOW
PRECIPITATION AND WIND EVENT CONTINUES EARLY THIS MORNING. VALLEY
RAIN AND MTN SNOW HAS BEEN FILLING IN AGAIN LAST HOUR OR SO ACROSS
THE NRN CWA AND LIKELY EXTENDS S OUT OF RADAR RANGE INTO CENTRAL
UT.

A COLD FRONT HAS PUSHED INTO CENTRAL UT BUT HAS BECOME ILL DEFINED
AS OF EARLY THIS MORNING. EXPECT A SECONDARY SWD PUSH OF LOW
LEVEL COLD AIR THIS AFTN AND THIS SHOULD TAKE THE PRECIP PLUME SWD
WITH IT BECOMING MORE SHOWERY AND TAPERING OFF ACROSS THE NORTH.

THE CORE OF STRONG WINDS AT 600 AND 700 MB ALSO SHIFTS S LATER
TODAY AND THE STRONG RIDGETOP WINDS IN THE NRN MTNS SHOULD START
TO DROP OFF. EXISTING WINTER STORM WARNINGS WILL REMAIN UNCHANGED.

EXPECT THE SURFACE GRADIENT TO TIGHTEN UP THIS AFTN ACROSS THE CWA
BEHIND THE SECONDARY COLD PUSH AND THIS SHOULD SEND WINDS BACK
INTO THE ADVISORY RANGE ACROSS THE NW DESERTS AND ACROSS THE
DOWNSLOPE CASTLE COUNTRY AREAS OF EASTERN UT WHERE ADVISORIES
REMAIN IN EFFECT.

THE FLOW BECOMES MORE NORTHERLY TONIGHT AS THE RIDGE ALONG THE
WEST COAST AMPLIFIES AND DRIES OUT. CLEARING SKIES AND A COLDER
AIRMASS IN PLACE SHOULD SEND LOW TEMPS QUITE A BIT LOWER TUE
MORNING THAN THEY HAVE BEEN. A STRONG SURFACE HIGH BUILDING TO
OUR NORTH TUE KEEPS THE AIRMASS VERY STABLE AND DONT EXPECT MUCH
RECOVERY FROM THE COLD MORNING TEMPS IN VALLEYS PRONE TO
INVERSIONS. TEMPS WILL BE CHILLY AGAIN TUE NIGHT BUT SWLY FLOW
PICKS UP WED AHEAD OF THE NEXT PAC TROF AND SHOULD PROVIDE ENOUGH
MIXING TO SEND TEMPS BACK UP WELL ABOVE NORMAL AGAIN.

&&

.LONG TERM (AFTER 00Z THURSDAY)...VERY ACTIVE LONG TERM PORTION OF THE
FORECAST...WITH A WINTER STORM EXPECTED TO IMPACT MUCH OF UTAH FOR
CHRISTMAS DAY. A FAIRLY COLD TROUGH WILL APPROACH THE PACIFIC COAST AT
THE BEGINNING OF THE LONG TERM FORECAST PERIOD. THIS TROUGH WILL
PROGRESS EASTWARD OVERNIGHT WEDNESDAY NIGHT.

A FAIRLY STRONG COLD FRONT ASSOCIATED WITH THIS SYSTEM WILL CROSS
WESTERN UTAH SOME TIME THURSDAY MORNING INTO EARLY THURSDAY
AFTERNOON. 700MB TEMPERATURES AHEAD OF THIS COLD FRONT NEAR 0C
ACROSS NORTHERN UTAH WILL QUICKLY FALL TO NEAR -10 TO -13C BEHIND
THE COLD FRONT. THE EXACT FRONTAL TIMING WILL REALLY IMPACT WHEN
THE RAIN/SNOW MIX WILL CHANGE TO ALL SNOW FOR THE VALLEY
LOCATIONS. MUCH OF THE MODEL GUIDANCES VARIES ON THE FRONTAL
TIMING BY ABOUT 6 HOURS OR SO...WITH SOME OF THE MODEL GUIDANCE
INDICATING A FRONTAL PASSAGE THURSDAY MORNING...WITH OTHER
GUIDANCE CLOSER TO THURSDAY AFTERNOON.

AS THE TROUGH CONTINUES EASTWARD ACROSS THE AREA THURSDAY...
PRECIPITATION WILL CONTINUE ACROSS MUCH OF THE CWA INTO THE
EVENING...BEFORE BECOMING A PREDOMINANTLY OROGRAPHICALLY DRIVEN
PRECIPITATION EVENT LATER THURSDAY NIGHT INTO EARLY FRIDAY. AT
THIS TIME...IT APPEARS THAT THE VALLEYS OF UTAH OUTSIDE OF DIXIE
WILL SEE ACCUMULATING SNOW THURSDAY AFTERNOON INTO THURSDAY NIGHT.
ONE OF THE MAIN QUESTIONS WITH THIS FORECAST IS WILL THE COLD
FRONT TIMING BE MORE LIKE THE FASTER GFS OR THE SLOWER
EC...CHANGING THE RAIN/SNOW MIX TO SNOW THURSDAY MORNING.

MODEL TO MODEL CONSISTENCY HAS BEEN LACKING WITH THIS SYSTEM OVER THE
PAST SEVERAL DAYS. HOWEVER...THE 00Z EC AND 00Z GFS HAVE BUCKED THIS
TREND. BOTH MODELS ARE ADVERTISING A STORM OF SIMILAR STRENGTH. AS
ALLUDED TO EARLIER...TIMING DIFFERENCES REMAIN...ESPECIALLY ASSOCIATED
WITH FRONTAL PASSAGE THURSDAY. LOOKING AT BOTH THE 12Z AND 00Z
CANADIAN...NAEFS AND GEFS RUNS...THE 12Z GFS WAS AN OUTLIER IN THE
ENSEMBLE GUIDANCE WITH A MAJORITY OF THE MEMBERS OF THE ENSEMBLES
SHOWING A STRONGER...DEEPER SYSTEM. THE 00Z ENSEMBLE DATA INDICATED A
BETTER OVERLAP BETWEEN THE GEFS AND THE CANADIAN ENSEMBLES...SHOWING A
FAIRLY STRONG AND COLD TROUGH. GIVEN THE INCREASING MODEL
CONSISTENCY...INCREASED POPS QUITE A BIT THURSDAY INTO FRIDAY. ALSO
INTRODUCED ACCUMULATING SNOW TO THE VALLEYS THURSDAY AFTERNOON/EVENING.

THOSE WITH PLANS TO TRAVEL THURSDAY MORNING THROUGH FRIDAY MORNING
SHOULD CONTINUE TO MONITOR FUTURE FORECASTS. ONE CONSISTENT POINT
REGARDLESS OF THE MODEL CHOSEN IS THAT IT WILL BECOME QUITE COLD BEHIND
THIS COLD FRONT AND REMAIN SO FOR MUCH OF THE REMAINDER OF THE EXTENDED
FORECAST PERIOD.

A BRIEF LULL IN THE ACTION IS EXPECTED FRIDAY AFTERNOON INTO SATURDAY
BEFORE ANOTHER TROUGH DIGS DOWN THE EAST SIDE OF THE EASTERN PACIFIC
HIGH AND MOVES INTO THE WESTERN UNITED STATES LATER SATURDAY.
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE 00Z EC AND THE 00Z GFS
CONTINUE FROM EARLIER RUNS. BUMPED POPS UP ABOVE CLIMO ACROSS THE
NORTHERN HALF OF UTAH SUNDAY INTO MONDAY TO REFLECT A PERIOD OF
UNSETTLED WEATHER ACROSS THE STATE. HARD TO LATCH ON TO ANY SPECIFIC
TIMING AT THIS POINT GIVEN MODEL TO MODEL INCONSISTENCIES.

&&

.AVIATION...SHOWERS WILL CONTINUE IN THE VICINITY OF THE SLC TERMINAL
THROUGH THE MORNING AND INTO THE EARLY AFTERNOON. CEILINGS ARE EXPECTED
TO REMAIN NEAR TO BELOW 6000 FEET AGL AND WILL OCCASIONALLY DIP
INTO MVFR RANGE UNTIL 18-21Z. SOUTHERLY WINDS ARE EXPECTED TO
SHIFT BACK TO THE NORTH TO NORTHWEST BETWEEN 12-15Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING UNTIL 6 PM MST THIS EVENING FOR UTZ007>010-
     517.

     WIND ADVISORY UNTIL 10 PM MST THIS EVENING FOR UTZ012.

     WIND ADVISORY UNTIL 8 PM MST THIS EVENING FOR UTZ005.

WY...NONE.
&&

$$

SHORT TERM...WILENSKY
LONG TERM/AVIATION...KRUSE

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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