Winter Storm Warning 12, NWS Salt Lake City, UT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
911 PM MDT MON SEP 28 2009

.SYNOPSIS...STRONG HIGH PRESSURE WILL KEEP AN UNSEASONABLY WARM
AIRMASS OVER THE GREAT BASIN THROUGH TUESDAY. A COLD PACIFIC STORM WILL
MOVE INTO THE GREAT BASIN LATE TUESDAY THROUGH WEDNESDAY...WITH
MUCH COOLER AIR LINGERING THROUGH THE REMAINDER OF THE WEEK.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS THE RIDGE AXIS HAS SHIFTED EAST
TO THE ROCKIES WITH A TROUGH APPROACHING THE PACIFIC NORTHWEST.
400-250MB ACARS WIND OBSERVATIONS PLACES A 80-110KT CYCLONICALLY
CURVED JET JUST OFF THE PACIFIC NORTHWEST. 00Z 700MB ANALYSIS SHOWS
A RIDGE FROM CENTRAL TEXAS NORTHWARD ALONG THE EASTERN SLOPES OF THE
ROCKIES...AND A COLD FRONT SLICING THROUGH THE PACIFIC NORTHWEST.
COOL ADVECTION WAS INITIATING LOCALLY WITH +13C AT KSLC AND +12C
UPSTREAM AT KDRA. 00Z KSLC RAOB INDICATES 5C OF WARMING BELOW 750MB
AND 5C OF COOLING ABOVE 600MB DURING THE PAST 24 HOURS.

GOES/RUC PRECIPITABLE WATER INDICATE VALUES OF A QUARTER TO THIRD OF
AN INCH...RISING TO NEAR A HALF INCH WITHIN AREAS OF CIRRUS.

ANOTHER DRY NIGHT...THOUGH EXPECTING INCREASING HIGH LEVEL CLOUDS AS
PACIFIC MOISTURE SHEARS NORTHEAST AHEAD OF THE NEXT SYSTEM. LOW
TEMPERATURES WILL BE QUITE MILD DUE TO THE WARM DAYTIME HIGHS AND
INCREASING SOUTHERLY FLOW.

WILL FRESHEN UP CURRENT HEADLINES AND HAZARDOUS WEATHER OUTLOOK.
OTHER THAN TWEAKING OVERNIGHT LOWS AND WINDS BASED ON LATEST
OBSERVATIONS AND GUIDANCE...NO OTHER UPDATES PLANNED AT THIS TIME.
SEE PREVIOUS DISCUSSION BELOW FOR DETAILED THOUGHTS OF THE NEXT
STORM SYSTEM.

GLOBAL MODELS REMAIN LOCK STEP WITH TIMING AND GENERAL STRUCTURE OF
SYSTEM....BUT NAM REMAINS ABOUT 4 TO 6 HOURS SLOWER IN TIMING AS IT
DIGS ENERGY A BIT FARTHER SOUTH IN NEVADA DURING THE DAY TUESDAY.
THE LAST SEVERAL NAM RUNS HAVE BEEN INCHING TOWARDS THE CONSISTENT
SOLUTIONS THAT BOTH THE EC/GFS HAVE BEEN ADVERTISING FOR THE LAST
SEVERAL DAYS NOW...SO HAVE DECIDED TO LOOK PAST THIS SOLUTION AND
CONTINUED TO BASE PACKAGE ON GLOBAL SUITE. ANTICIPATE NAM WILL
LIKELY BECOME MORE RELIABLE WITHIN THE NEXT 24 HOURS AS THE TROUGH
BEGINS TO PUSH ON SHORE.

FIRST PRESSING WEATHER ISSUE WILL BE THE WINDS ON TUESDAY
AFTERNOON AND EVENING. A HIGH WIND WATCH WAS ISSUED THIS MORNING
FOR PORTIONS OF WESTERN/SOUTHERN UTAH AS 700MB SOUTHWESTERLIES
WILL INCREASE TO 45 TO 55 KNOTS IN THE PRE FRONTAL ENVIRONMENT
DURING THAT TIME. THIS COUPLED WITH SURFACE LOW BOMBING OUT TO
NEAR 995MB OVER NORTHWESTERN UTAH WILL DRIVE VERY STRONG WINDS
ACROSS THE REGION. GFS/EC TIME FRONTAL PASSAGE AT KENV AROUND
00Z WED...THEN PROGRESS IT STEADILY WEST TO EAST FROM THERE THROUGH
THE EVENING HOURS IN THE WEST...EVENTUALLY TO THE COLORADO BORDER
WEDNESDAY MORNING. ANTICIPATE POST FRONTAL WINDS WILL BE STRONGER
THAN PRE FRONTAL FOR PORTIONS OF THE WEST DESERT...INCLUDING THE
INTERSTATE 80 CORRIDOR IN WESTERN TOOELE VALLEY...SO HAVE ADDED
SPECIAL WORDING IN WATCH TO RELAY THIS.

HAVE ISSUED THE FIRST WINTER STORM WATCH OF THE SEASON FOR
ELEVATIONS OVER 8000FT THIS AFTERNOON FOR THE WASATCH/BEAR RANGES
AND UINTA MOUNTAINS FROM LATE TUESDAY EVENING THROUGH MIDDAY
THURSDAY. ALTHOUGH THE WATCH HIGHLIGHTS THE ENTIRE ZONE FOR EACH
OF THE ABOVE REGIONS ON THE WEB PAGE...HAVE PARSED OUT ELEVATIONS
BELOW 8000FT IN THE WATCH AS COMBINATION OF TIME OF YEAR AND WARM
WEATHER OF LATE SHOULD LIMIT THE BULK OF SIGNIFICANT ACCUMULATIONS
TO ABOVE 8000FT ACROSS THOSE ZONES. ANTICIPATE ACCUMULATIONS TO
GENERALLY RANGE FROM 6 TO 12 INCHES OVER THE WATCH AREA...BUT
NORTHWEST FLOW FAVORED AREAS...ESPECIALLY UPPER LITTLE COTTONWOOD
CANYON...MAY SEE ACCUMULATIONS UP TO 20 INCHES BY THURSDAY
AFTERNOON.

PROGRESSION OF TROUGH WEDNESDAY EVENING AND OVERNIGHT IS CRUCIAL
FOR POTENTIAL OF LOW ELEVATION SNOWFALL ALONG THE WASATCH FRONT.
SLOWER NAM DOES INDICATE LAKE BAND FORMATION OVER THE SALT LAKE
AND EASTERN TOOELE VALLEYS DURING THE OVERNIGHT HOURS...AS DEEP
INSTABILITY WOULD LINGER INTO A MORE FAVORABLE DIURNAL REGIME.
EXPECT IF PROGRESSION IS CLOSER TO GFS...WE MAY ONLY SEE BRIEF
ENHANCED CONVECTION DOWNWIND OF THE GSL. REGARDLESS...700 TEMPS
AND WET BULB ZERO SUPPORT SNOW NEARING VALLEY DURING THE OVERNIGHT
HOURS...BUT ACCUMULATIVE POTENTIAL SHOULD REMAIN HIGH BENCHES AND
ABOVE.

RAPID HEIGHT RISES ON THURSDAY WILL SQUELCH ALL BUT THE MOST
STUBBORN SNOW SHOWERS BY MIDDAY. ANTICIPATE SHORT WAVE RIDGING
WITH WARMING TEMPS WILL DOMINATE THEREAFTER THROUGH EARLY
WEEKEND...BUT GLOBAL SUITE INSISTS ON A RETURN TO ACTIVE WEATHER
BY EARLY NEXT WEEK.

&&

.AVIATION...SOUTHERLY WINDS ARE EXPECTED TO CONTINUE THROUGHOUT THE
EVENING AND INTO THE OVERNIGHT HOURS. AN ENHANCED DRAINAGE WIND IS
EXPECTED TONIGHT AHEAD OF THE NEXT PACIFIC SYSTEM AT THE SALT LAKE
TERMINAL.

WINDS ARE EXPECTED TO BECOME QUITE STRONG TUESDAY AFTERNOON INTO
EARLY WEDNESDAY MORNING. SOUTHWEST WINDS OF 30 TO 40 MPH WITH GUSTS
TO 60 MPH WILL BE POSSIBLE AHEAD OF A STRONG COLD FRONT. THE COLD
FRONT IS EXPECTED TO MOVE ACROSS THE TERMINAL LATE TUESDAY
EVENING SHIFTING THE STRONG WINDS TO THE NORTHWEST BEFORE
DIMINISHING WEDNESDAY MORNING.

&&

.FIRE WEATHER....THE COLD UPPER LEVEL TROUGH CURRENTLY OFF THE
PACIFIC NORTHWEST COAST WILL MOVE INTO THE WESTERN GREAT BASIN
TUESDAY. THE ASSOCIATED COLD FRONT AHEAD OF THE TROUGH WILL REACH
NORTHWEST UTAH BY TUESDAY EVENING...THEN SWEEP EAST ACROSS AND
THEN OUT OF THE STATE BY LATE WEDNESDAY. STRONG SOUTHERLY WINDS
AHEAD OF THE FRONT WILL BE FOLLOWED BY VERY COLD TEMPERATURES FOR
WEDNESDAY. MOST PRECIPITATION WILL REMAIN WITH THE COLDEST AIR
ALONG AND BEHIND THE FRONT ACROSS THE NORTHERN HALF OF THE STATE.
COLD TEMPERATURES WILL LINGER INTO THURSDAY...THEN A GRADUAL
WARMING TREND WILL SET UP LATE IN THE WEEK.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WATCH FROM 9 PM TUESDAY TO NOON THURSDAY FOR
     UTZ007-UTZ008-UTZ009.

    RED FLAG WARNING FROM NOON TUESDAY TO 9 PM TUESDAY FOR UTZ003-
    UTZ005-UTZ014-UTZ015-UTZ016-UTZ019.

     HIGH WIND WATCH FROM NOON TUESDAY TO 6 AM WEDNESDAY FOR UTZ003-
     UTZ004-UTZ005-UTZ015-UTZ016-UTZ019-UTZ020.

WY...NONE.

&&

PUBLIC...ROGOWSKI/MERRILL
FIRE WEATHER...CONGER
AVIATION...KRUSE

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

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
506 PM MDT MON SEP 28 2009

UTZ001>016-019>021-517-518-WYZ021-291000-
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-
506 PM MDT MON SEP 28 2009

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

.DAY ONE...TONIGHT

A MILD NIGHT IS IN STORE. SOUTHERLY WINDS WILL BEGIN TO INCREASE
AHEAD OF THE NEXT STORM SYSTEM.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH MONDAY

STRONG GUSTY SOUTHERLY WINDS WILL DEVELOP ACROSS MUCH OF THE AREA
TUESDAY. THOSE WITH WIND SENSITIVE OPERATIONS WILL NEED TO TAKE
PRECAUTIONS.

THESE STRONG WINDS WILL COMBINE WITH THE VERY DRY AIRMASS OVER
THE REGION TO RESULT IN CRITICAL FIRE WEATHER CONDITIONS ACROSS
PORTIONS OF THE STATE TUESDAY.

A COLD PACIFIC STORM IS FORECAST TO MOVE INTO THE WESTERN GREAT
BASIN TUESDAY AND INTO THE OUTLOOK AREA TUESDAY NIGHT AND
WEDNESDAY. THIS SYSTEM WILL BRING A DRAMATIC CHANGE IN THE WEATHER
WITH TEMPERATURES WEDNESDAY COOLING 30 TO 40 DEGREES FROM MONDAYS
HIGHS.

WIDESPREAD PRECIPITATION IS EXPECTED FROM THIS STORM OVER MAINLY
THE NORTHERN HALF OF UTAH. SNOW LEVELS WILL FALL TO AROUND
6000 FEET AND COULD BE LOCALLY LOWER. THIS STORM WILL LIKELY BRING
THE FIRST SIGNIFICANT SNOWFALL TO THE HIGH COUNTRY WEDNESDAY
THROUGH WEDNESDAY NIGHT.

FREEZING TEMPERATURES ARE EXPECTED ACROSS MUCH OF THE STATE WEDNESDAY
NIGHT.

THOSE WITH OUTDOOR INTERESTS AT HIGHER ELEVATIONS WHO WOULD BE
IMPACTED BY SNOW AND COLDER WEATHER SHOULD BE MAKING PREPARATIONS
FOR THIS EVENT.

.SPOTTER INFORMATION STATEMENT...

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

ROGOWSKI

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