Heavy Snow in Utah, January 15 to 16, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
220 PM MST SAT JAN 14 2006

.SYNOPSIS...STRONG SOUTHWESTERLY FLOW ALOFT WILL REMAIN ACROSS THE
REGION THIS EVENING...IN ADVANCE OF AN APPROACHING PACIFIC STORM
SYSTEM. THIS STORM WILL IMPACT THE AREA LATE TONIGHT THROUGH SUNDAY
NIGHT AND BRING SIGNIFICANT SNOWFALL.

&&

.DISCUSSION...MILD SOUTHERLY FLOW COVERS UTAH EARLY THIS AFTERNOON.
GUSTY SOUTHWEST WINDS WILL CONTINUE ESPECIALLY WESTERN HALF OF UTAH
THIS AFTERNOON AND EVENING AS STRONGEST WINDS ALOFT MOVE IN. PARTS
OF THE SALT LAKE/TOOELE VALLEYS AND WESTERN VALLEYS HAVE SEEN GUSTS
OVER 30 MPH. STORM SYSTEM CONTINUES TO MOVE EAST ACROSS THE CENTRAL
SIERRA NEVADA. SURFACE LOW DEEPENING OVER NORTHEAST NEVADA PAST
COUPLE HOURS IS DEEPER THAN GFS OR NAM PROGGED. SURFACE COLD FRONT
ASSOCIATED WITH THIS WAVE WILL REACH THE GSL BY 06Z AND THEN MOVE
ACROSS THE WASATCH FRONT AFTER MIDNIGHT. PRECIPITATION WILL DEVELOP
ALONG AND ESPECIALLY BEHIND THIS FRONT AS THE 700 MB BAROCLINIC ZONE
AND LEADING PERIOD OF PVA MOVES FROM WEST TO EAST INTO UTAH. THUS
PRECIPITATION WILL QUICKLY DEVELOP ALONG THE ENTIRE I-15 CORRIDOR
INTO SOUTHWEST UTAH LATER TONIGHT. SNOW LEVELS WILL CRASH WITH THE
HEAVY BAND OF PRECIPITATION AND COLD AIR ADVECTION. SNOW SHOULD
REACH THE VALLEY FLOORS OF NORTHERN UTAH BY 5AM. HAVE UPGRADED
WINTER STORM WATCHES IN THE WESTERN VALLEYS TO HEAVY SNOW WARNINGS
AND IN THE MOUNTAINS TO WINTER STORM WARNINGS. ALSO INCLUDED THE
CACHE VALLEY AND SOUTHWEST WYOMING FOR SNOW ADVISORIES.

COLD AIR ADVECTION IN THE LOW LEVELS WILL CONTINUE THROUGH SUNDAY
EVENING. ALOFT THE UPPER TROF LAGS BEHIND OVER NEVADA SO AS WINDS
ALOFT VEER TO WEST AND THEN NORTHWEST WITH THE UPPER TROUGH AXIS
LATE IN THE DAY THERE WILL CONTINUE TO BE COLD AIR ADVECTION AT 500
MB AND RIPPLES OF PVA FLOWING ACROSS MOST OF UTAH. THUS AFTER A
BRIEF BREAK THE PRECIPITATION SHOULD FILL BACK IN DURING THE MORNING
AND ENHANCE ON I-15 CORRIDOR NORTHWEST FACING AREAS. THE STRONGEST
PIECE OF ENERGY PROGGED BY THE 18Z NAM AND 12Z GFS AND 18Z UKMET
WILL DIVE INTO NORTH CENTRAL UTAH SUNDAY EVENING AND DROP INTO
NORTHERN ARIZONA. THIS HAS THE COLDEST AIR ALOFT WITH A POCKET OF
-32C AT 500MB AND -15 TO -16C AT 700MB. HEAVY SNOW WILL CONTINUE
ALONG THE I-15 CORRIDOR IN THE EVENING THEN TAPER OFF AFTER
MIDNIGHT. SOUTH OF THE GREAT SALT LAKE AND MOST FAVORED UPSLOPE
AREAS WILL CONTINUE TO HAVE PERIODS OF SNOW OVERNIGHT. INSTABILITY
ACROSS THE LAKE STILL APPEARS SUFFICIENT FOR LAKE ENHANCEMENT AND
POSSIBLE LAKE BAND FORMING SUNDAY NIGHT. THAT IS -16C AIR AT 700 MB
OVER 2C WATER AND STEEP LAPSE RATES TO 500 MB.

AS THE UPPER TROF AXIS PASSES THE FLOW WILL BECOME MORE NORTHERLY
WITH TIME EARLY MONDAY. SNOW SHOWERS MAY LINGER INTO MONDAY MORNING
ESPECIALLY DOWNWIND OF THE LAKE AND NORTH FLOW UPSLOPE AREAS WERE
LOW LEVEL MOISTURE REMAINS UNDER THE RAPIDLY LOWERING INVERSION.
MOST SNOW SHOULD END IN THE MORNING. A PERIOD OF GUSTY NORTH WINDS
WILL AFFECT THE MOUNTAINS BEFORE THE INVERSION LOWERS AS THE UPPER
JET MAX PASSES BY MONDAY MORNING.

ANOTHER ISSUE SUNDAY NIGHT AND MONDAY MORNING WILL BE THE STRONG
COLD AIR ADVECTION IN SOUTHWEST UTAH AND RESULTANT STRONG LOW LEVEL
WINDS THAT DEVELOP. THIS MAY NEED A HIGH WIND WATCH BUT AT LEAST A
SOLID ADVISORY FOR GAP AREAS IN SOUTHWEST UTAH.

WARM AIR ADVECTION IN NORTHWEST FLOW WITH THE UPPER RIDGE
APPROACHING MONDAY NIGHT WILL SPREAD CLOUDS INTO NORTHERN UTAH. THIS
WILL HAVE SOME LIGHT SNOW AS WELL...ESPECIALLY OVER THE NORTHERN
MOUNTAINS INTO TUESDAY. THIS MAY KEEP MINIMUM TEMPERATURES UP IN THE
NORTHERN UTAH WHILE SOUTHERN UTAH RADIATES VERY WELL.

NEXT SYSTEM STILL ON TRACK TO SPILL INTO NORTHERN UTAH LATE TUESDAY
NIGHT AND SWING THROUGH WITH A DECENT COLD FRONT ON WEDNESDAY PER
12Z GFS AND ECMWF. THIS COULD PRODUCE SIGNIFICANT SNOWFALL BUT IT IS
NOT AS STRONG AS SUNDAYS STORMS. A COLD NORTHWEST FLOW PREVAILS THE
REST OF THE WEEK WITH ADDITIONAL DISTURBANCES KEEPING PERIODS OF
SNOW...ESPECIALLY IN NORTHERN UTAH.

&&

.AVIATION...SEE LATEST SLCTAFSLC.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING FROM MIDNIGHT SUNDAY TO 5 AM MONDAY FOR
     UTZ014>18.
     HEAVY SNOW WARNING 1 AM SUNDAY TO 5 AM MONDAY FOR UTZ002>004
     HEAVY SNOW WARNING 1 AM SUNDAY TO 5 AM MONDAY FOR UTZ014>016
     SNOW ADVISORY 1 AM SUNDAY TO 11 PM SUNDAY EVENING UTZ001
WY...SNOW ADVISORY 1 AM SUNDAY TO 11 PM SUNDAY EVENING WYZ021

&&

TARDY

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