Winter Storm and Avalanche in Utah, April 4 to 6, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
1027 AM MDT SUN APR 4 2010

.SYNOPSIS...A COLD AND ENERGETIC PACIFIC STORM SYSTEM OFF THE
PACIFIC NORTHWEST COAST TODAY WILL MOVE SOUTHEAST INTO THE GREAT
BASIN FOR MONDAY THROUGH TUESDAY. HIGH PRESSURE ALOFT WILL RETURN
TO THE AREA FOR THE MIDDLE AND LATTER PORTIONS OF THE WEEK.

&&

.DISCUSSION...THE COLD CORE UPPER LOW OFF THE PACIFIC NW COAST
THIS MORNING STILL ON TRACK TO BECOME A MAJOR STORM FOR PORTIONS OF
THE INTERMOUNTAIN WEST EARLY THIS WEEK. A STRONG UPPER LEVEL JET
ON THE WEST SIDE OF THIS LOW WILL DIG SE AND SERVE TO ELONGATE THE
UPPER LOW NW-SE INTO THE WRN GREAT BASIN LATE TONIGHT. THIS
COMPLEX NEGATIVE-TILT FEATURE WILL SHIFT EAST ACROSS UTAH MONDAY
NIGHT...FOLLOWED BY A CYCLONIC NW FLOW EARLY TUESDAY.

THE INITIAL PRECIP WITH THIS TROUGH WILL LARGELY BE DRIVEN BY
INCREASINGLY DEEP/MOIST AND STRONG WARM ADVECTION TONIGHT/EARLY
MONDAY. FAIRLY STRONG THERMALLY DRIVEN UPWARD MOTIONS COULD EASILY
DEVELOP TONIGHT...WITH SOME OF THE NRN UTAH HIGH TERRAIN SEEING
HEAVY PRECIP DEVELOP LATE TONIGHT. THIS WOULD BE ESPECIALLY TRUE
ALONG SW FACING SLOPES RUNNING NORMAL TO THE MEAN FLOW. THE 12Z
NAM DOES SUGGEST THAT THE TIMING OF THE CURRENT WATCH MAY BE A BIT
LATE IN THE START TIME. WILL GET A LOOK AT THE REMAINING MODELS AS
THEY COME IN...BUT FOR NOW WILL LEAVE WINTER WEATHER HIGHLIGHTS AS
ISSUED EARLIER.

THE ASSOCIATED COLD FRONT WITH THE UPPER TROUGH WILL STILL REACH
NW UTAH MONDAY MORNING...THE SWEEP INTO EXTREME SRN/SERN UTAH
MONDAY EVENING. THE TIMING OF THE FRONTAL PASSAGE HAS OVER THE
PAST COUPLE OF MODEL RUNS HAS BEEN CREEPING LATER INTO
MONDAY...WITH THE 12Z NAM HINTING THAT THE STRONGEST LOW-LEVEL
COLD ADVECTION MAY LAG BACK INTO THE MID/LATE AFTERNOON. THIS
SLOWING OF THE FRONT WOULD AFFECT HEAVY SNOW TIMING MORE THAN
AMOUNTS/INTENSITY. ALSO...THIS WOULD BRING CONCERNS WITH DEEP
CONVECTION IF THE FRONT HOLDS OFF UNTIL MAX HEATING.

THE AIRMASS OVER UTAH LATE MONDAY/TUESDAY WILL BE ONE OF DEEP-
LAYER MOISTURE/INSTABILITY AS INDICATED THROUGH MODEL TIME/HEIGHT
SECTIONS. THIS AIRMASS IN CONCERT WITH A SERIES OF WEAK VORTICITY
MAXIMA MOVING THROUGH THE MEAN TROUGH POSITION WILL RESULT IN A
PROLONGED PERIOD OF MOSTLY SNOW MONDAY AFTERNOON THROUGH AT LEAST
TUESDAY MORNING. THE FOCUS OF HEAVY SNOW WILL BE OF THE HIGHER
TERRAIN OF NRN/CNTRL UTAH AND THE ADJACENT WRN VALLEYS. AN IDEAL
SITUATION FOR AN HEAVY OROGRAPHIC EVENT SETTING UP...ESPECIALLY
ALONG THE SRN HALF OF THE WASATCH RANGE SOUTH INTO CNTRL UTAH
MOUNTAINS.

WARMING ALOFT LATE TUESDAY WILL BRING A GRADUAL END TO SNOW ACROSS
THE STATE. HIGH PRESSURE ALOFT WILL DOMINATE WEDNESDAY/THURSDAY. A
SERIES OF SHORTWAVES RACING EAST OVER THE TOP OF THE RIDGE THROUGH
THE NRN ROCKIES/NRN GREAT BASIN MAY BRING SOME LIGHT PRECIP TO THE
FAR NRN ZONES FRIDAY. A DEEPENING TROUGH OVER THE ERN PACIFIC WILL
BACK THE MEAN FLOW ALOFT OVER THE INTERIOR WEST AND DRIVE TEMPS
AND WINDS UPWARD SATURDAY/SATURDAY NIGHT. PRECIP ASSOCIATED THE
APPROACHING TROUGH COULD REACH WRN UTAH LATE SUNDAY.

&&

.AVIATION...WIND DIRECTION WILL CONTINUE TO BE DIFFICULT AT THE SLC
TERMINAL THROUGH 21Z. A MAINLY SOUTHERLY FLOW IS EXPECTED THROUGH
18Z AT LEAST...WITH A SHIFT TO THE NORTH TO NORTHWEST EXPECTED
BETWEEN 18 AND 21Z.

A TEMPORARY PERIOD OF CEILINGS BELOW 7000 FEET AGL IS POSSIBLE THIS
MORNING THROUGH 18Z. THERE IS A 10 PERCENT CHANCE OF A BRIEF HIGH
END MVFR CEILING DURING THIS TIME.

NOTE...EFFECTIVE AT 15Z TUESDAY APRIL 6 2010 THE SALT LAKE CITY WFO
WILL BEGIN 3 HOURLY TAF ISSUANCES FOR KSLC. THE INTERMEDIATE TAF
ISSUANCES AT 03Z...09Z...15Z...AND 21Z WILL BE ISSUED AS AMENDMENTS
TO THE TAFS ISSUED AT 00Z...06Z...12Z AND 18Z. THE INTERMEDIATE TAFS
WILL BE ISSUED DURING A 20 MINUTES WINDOW BETWEEN 10 MINUTES BEFORE
THE HOUR AND 10 MINUTES AFTER THE HOUR.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WATCH FROM LATE TONIGHT THROUGH TUESDAY AFTERNOON
     FOR UTZ007>009.

     WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON
     FOR UTZ010-517.

WY...NONE.

&&

PUBLIC...CONGER
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)

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
516 AM MDT SUN APR 4 2010

UTZ001>016-019>021-517-518-WYZ021-051215-
CACHE VALLEY/UTAH PORTION-NORTHERN WASATCH FRONT-
SALT LAKE AND TOOELE VALLEYS-SOUTHERN WASATCH FRONT-
GREAT SALT LAKE DESERT AND MOUNTAINS-WASATCH MOUNTAIN VALLEYS-
WASATCH MOUNTAINS I-80 NORTH-WASATCH MOUNTAINS SOUTH OF I-80-
WESTERN UINTA MOUNTAINS-WASATCH PLATEAU/BOOK CLIFFS-
WESTERN UINTA BASIN-CASTLE COUNTRY-SAN RAFAEL SWELL-
SANPETE/SEVIER VALLEYS-WEST CENTRAL UTAH-SOUTHWEST UTAH-
UTAHS DIXIE AND ZION NATIONAL PARK-SOUTH CENTRAL UTAH-
GLEN CANYON RECREATION AREA/LAKE POWELL-CENTRAL MOUNTAINS-
SOUTHERN MOUNTAINS-SOUTHWEST WYOMING-
516 AM MDT SUN APR 4 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN TWO THIRDS OF
UTAH AND SOUTHWEST WYOMING.

.DAY ONE...TODAY AND TONIGHT

SOUTH WINDS WILL INCREASE TODAY WITH LOCALLY STRONG WINDS ACROSS
SOUTHERN UTAH LATE THIS AFTERNOON THROUGH THIS EVENING.

SNOW WILL DEVELOP ACROSS THE NORTHERN MOUNTAINS OVERNIGHT.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THE NEXT STORM SYSTEM WILL PUSH A COLD FRONT ACROSS THE AREA
MONDAY...BRINGING WIDESPREAD SNOW TO THE AREA. GUSTY SOUTHERLY
WINDS WILL OCCUR AHEAD OF THIS FRONT IN SOUTHERN UTAH ON MONDAY.
SIGNIFICANT ACCUMULATIONS ARE EXPECTED IN THE MOUNTAINS AND
HIGHER VALLEYS THROUGH TUESDAY.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)