Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 281253
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
553 AM MST SUN DEC 28 2014

.SYNOPSIS...THE COLD STORM SYSTEM WILL SETTLE INTO THE AREA  THROUGH
EARLY MONDAY. A SECOND STORM SYSTEM WILL IMPACT MAINLY THE SOUTHERN
HALF OF THE UTAH MIDWEEK.

&&

.SHORT TERM (THROUGH 12Z WEDNESDAY)...UPPER TROUGH CURRENTLY OVER
THE PACIFIC NORTHWEST WILL CONTINUE TO DIVE INTO THE EASTERN GREAT
BASIN TODAY. WARM ADVECTION STRENGTHENED OVERNIGHT OVER NORTHERN
UTAH...GENERATING CLOUDS AND SNOW. ALTHOUGH KMTX REGISTERED HIGHER
REFLECTIVITIES THROUGH THE NIGHT...THE BULK OF THE SNOW SEEMED TO
HAVE FALLEN OVER THE HIGH TERRAIN. LOGAN SUMMIT WEBCAM SHOWED
ACCUMULATING SNOW BUT A WEDGE OF DRIER AIR REMAINED IN PLACE IN THE
ADJACENT VALLEYS...AS INDICATED BY TEMPERATURES IN THE MID 20S AND
DEWPOINTS IN THE MID TEENS AT BOTH LOGAN AND BRIGHAM CITY.

LAPSE RATES WILL STEEPEN THROUGHOUT THE MORNING HOURS AS COLDER AIR
ALOFT SAGS INTO NORTHERN UTAH...PRECEDING THE 700MB COLD ADVECTION
WHICH OCCURS LATER THIS MORNING. THIS IN TURN PRECEDES THE SURFACE
BOUNDARY WHICH IS NOT EXPECTED THROUGH NORTHERN UTAH UNTIL THE
AFTERNOON AND EVENING HOURS. MORE RAPID DEVELOPMENT OF SNOW ACROSS
NORTHERN UTAH IS EXPECTED THROUGH THE DAY AS THIS OCCURS. THIS
SHOULD HELP MOISTEN THE AIRMASS ENOUGH TO BRING MEASURABLE
PRECIPITATION TO THE VALLEY FLOORS. BULK OF PRECIPITATION THIS
MORNING WILL LIKELY AFFECT AREAS NORTH OF I-80. THE SALT LAKE AND
UTAH VALLEYS AND SOUTHERN WASATCH MOUNTAINS WILL LIKELY SEE MORE
INTENSE PRECIPITATION THIS AFTERNOON AND EVENING...NEAR AND BEHIND
THE SURFACE FRONT. THE FRONT WILL CONTINUE ACROSS CENTRAL UTAH THIS
EVENING AND PUSH THROUGH SOUTHERN UTAH OVERNIGHT. ACCUMULATING SNOW
IS EXPECTED ACROSS CENTRAL UTAH WITH THE FRONT...BUT THE UPPER LEVEL
SUPPORT STARTS TO WANE ACROSS THE SOUTH FOR A SMALLER CHANCE OF
PRECIPITATION.

PERIODS OF LIGHT SNOW WILL CONTINUE ACROSS MUCH OF NORTHERN AND
CENTRAL UTAH TOMORROW AS MODELS INDICATE A WEAK CIRCULATION SPINNING
UP OVER NORTHERN UTAH AHEAD OF ANOTHER REINFORCING TROUGH WHICH WILL
CARVE SOUTH ALONG THE WEST COAST STATES TOMORROW INTO TUESDAY. THIS
TROUGH WILL DRIVE EASTERLY WINDS WHICH WILL DRAW ARCTIC AIR ACROSS
THE DIVIDE. THE MUCH COLDER AIRMASS STARTS TO ENTER SOUTHWEST
WYOMING AND NORTHEAST UTAH TOMORROW...SPILLING INTO THE REMAINDER OF
UTAH TOMORROW NIGHT THROUGH TUESDAY. ENHANCED EASTERLIES WILL BRING
LOCALLY STRONG AND GUSTY WINDS TO PORTIONS OF THE
AREA...PARTICULARLY ALONG THE WASATCH FRONT NEAR CANYONS.

THE ARCTIC BOUNDARY WILL BE ASSOCIATED WITH LIGHT SNOW ACROSS
NORTHERN UTAH AS THE AIRMASS WILL BE FAIRLY DRY. HOWEVER...THINGS
GET MORE INTERESTING FARTHER SOUTH ON TUESDAY. THE TROUGH IS PROGGED
TO PINCH OFF INTO A CLOSED LOW OVER CALIFORNIA ON TUESDAY BEFORE
SLOWLY TRACKING EAST ACROSS THE DESERT SOUTHWEST. THE 700MB BOUNDARY
WILL STRENGTHEN ACROSS CENTRAL/SOUTHERN UTAH ON TUESDAY AS WARM
ADVECTION DEVELOPS ACROSS ARIZONA AHEAD OF THE LOW. THIS WILL INDUCE
STRONGER LIFT WHICH WILL FIRE UP HEAVIER PRECIPITATION ALONG THE
BOUNDARY. SNOW IS POSSIBLE EVEN DOWN TO ST GEORGE ESPECIALLY TUESDAY
NIGHT GIVEN THE COLD AIR BEHIND THE ARCTIC BOUNDARY. HOWEVER...SOME
UNCERTAINTY STILL EXISTS WITH THE POSITIONING OF THIS BOUNDARY...SO
HAVE NOT RAISED POPS TOO SIGNIFICANTLY AS OF THIS FORECAST PACKAGE.

WINTER WEATHER HIGHLIGHTS CONTINUE WITH THE ONLY CHANGE THIS MORNING
BEING THE ADDITION OF A WINTER WEATHER ADVISORY FOR SOUTHWEST
WYOMING. WHILE SNOWFALL AMOUNTS THERE SEEM MARGINAL...ACCUMULATING
SNOW COMBINED WITH SOME GUSTY WINDS BOTH THIS AFTERNOON AND AGAIN
TOMORROW BEHIND THE ARCTIC BOUNDARY WILL LIKELY HAVE SOME IMPACTS ON
POST-HOLIDAY TRAVEL. CENTRAL UTAH ZONES POTENTIALLY MAY NEED
HIGHLIGHTS...BUT WILL LET THE DAY SHIFT LOOK AT THIS MORE CLOSELY AS
IMPACTS WILL BE MINIMAL UNTIL THIS EVENING. ANY WIND/SNOW CONCERNS
WITH THE ARCTIC AIRMASS WILL BE ADDRESSED IN THE NEXT FEW SHIFTS AS
THE EVENT GETS CLOSER.

&&

.LONG TERM (AFTER 12Z WEDNESDAY)...THE CLOSED LOW IS EXPECTED TO
DIVE SOUTH TUESDAY NIGHT...AND SHOULD BE CENTERED OVER SOUTHERN
CALIFORNIA BY WEDNESDAY MORNING. IT IS THEN EXPECTED TO SLOWLY TRACK
EASTWARD ACROSS ARIZONA THROUGH THURSDAY BEFORE MOVING INTO NEW
MEXICO ON FRIDAY. THIS WILL MOVE THE FOCUS OF MOISTURE AND
INSTABILITY OVER THE FORECAST AREA INTO SOUTHERN UTAH...RESULTING IN
A RELATIVELY LONG PERIOD OF PRECIPITATION. A RATHER COLD AIRMASS
WITH 700 MB TEMPS AS LOW AS -14C WILL DROP SNOW LEVELS DOWN PERHAPS
AS LOW AS DIXIE. MODELS HAVE BEEN RATHER CONSISTENT WITH THE TRACK
OF THE LOW SO MADE ONLY A FEW CHANGES TO POPS DURING THIS PERIOD.
THE TRACK OF THE LOW WILL MAINTAIN AN E/NE FLOW OVER MUCH OF THE
FORECAST AREA...WHICH WILL ALLOW SOME ENHANCED CANYON WINDS TO
CONTINUE...PRIMARILY OVER NORTHERN UTAH.

PRECIPITATION IS EXPECTED TO TAPER OFF BY FRIDAY AS THE MOISTURE AND
INSTABILITY FROM THE STORM MOVE OUT OF THE FORECAST AREA...ALLOWING
A GRADUALLY WARMING NORTHWEST FLOW TO SETTLE IN ON THE FRONT SIDE OF
A BUILDING PACIFIC RIDGE. WEAK WAVES MOVING OVER THE FRONT SIDE OF
THE RIDGE ARE EXPECTED TO PUSH ENOUGH MOISTURE OVER NORTHERN UTAH TO
KEEP THE THREAT OF SOME PRIMARILY HIGHER TERRAIN PRECIPITATION IN
THE FORECAST THROUGH DAY 7 AS TEMPERATURES CREEP BACK TOWARD
SEASONAL NORMS.

&&

.AVIATION...AT THE SLC TERMINAL...VFR CONDITIONS WITH CIGS AT OR
BELOW 6000 FT AGL ARE EXPECTED TO DETERIORATE INTO THE IFR RANGE
BEGINNING BETWEEN 18Z AND 20Z AS SNOW MOVES IN. THERE IS A 30
PERCENT CHANCE OF OCCASIONAL IFR CONDITIONS BEGINNING SOONER THAN
THAT. COLD SURFACES WILL ALLOW SNOW TO ACCUMULATE ON UNTREATED
SURFACES...WITH 1 TO 3 INCHES OF SNOW EXPECTED THROUGH MONDAY.
SOUTHEAST WINDS ARE EXPECTED TO SHIFT TO THE NORTHWEST BETWEEN 19Z
AND 22Z WITH THE PASSAGE OF A COLD FRONT.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING FROM NOON TODAY TO 4 PM MST MONDAY FOR
     UTZ003-004-010.

     WINTER STORM WARNING UNTIL 4 PM MST MONDAY FOR UTZ001-002-
     006>009.

WY...WINTER WEATHER ADVISORY UNTIL 10 PM MST MONDAY FOR WYZ021.
&&

$$

CHENG/TRAPHAGAN

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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