Heavy Snow in Wyoming, March 11, 2014

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1117 PM MDT MON MAR 10 2014

.UPDATE...
ISSUED AT 827 PM MDT MON MAR 10 2014

00Z KUNR SOUNDING HAD PWATS OF 177 PERCENT OF NORMAL...BUT THERE
WAS A DRIER LAYER BELOW 700MB. 02Z SURFACE ANALYSIS HAD LOW
PRESSURE OVER CENTRAL WY WITH COLD FRONT FROM LOW INTO SOUTH
CENTRAL SD. COLD AIR FILTERING INTO CWA WITH READINGS IN THE MID
30S OVER NORTHWEST SD AND OVER THE HIGHER ELEVATIONS OF THE BLACK
HILLS. WATER VAPOUR HAD INITIAL SHORTWAVE OVER CENTRAL WY WITH
BAND OF PRECIPITATION FROM SOUTH CENTRAL MT TO NORTH CENTRAL SD.
MAINLY -RA OVER CWA AT THIS POINT. MAIN SHORTWAVE SPINNING
VIGOROUSLY OVER ID/WY/MT BORDER WITH SOME LIGHTNING STRIKES.
SHORTWAVE WILL MOVE EAST TONIGHT/TUESDAY MORNING. 110KT JET STREAK
AHEAD OF WAVE COMBINED WITH 90KT JET STREAK OVER THE UPPER MIDWEST
WILL COUPLE TO BRING STRONG SYNOPTIC SCALE LIFT OVER THE CWA FROM
06Z-18Z. LIFT WILL LINK UP WITH STRONG BAROCLINIC ZONE FROM
850-700MB BEHIND COLD FRONT. STRONG BAND OF FRONTOGENESIS NOTED
WITH RATHER WELL-DEFINED QG-FORCING. EXPECT PRECIPITATION TO
CONTINUE TO INTENSIFY AHEAD OF MAIN SHORTWAVE RESULTING IN DYNAMIC
COOLING AND CHANGE OVER FROM RAIN TO SNOW FROM NORTH TO SOUTH.

PREVIOUS FORECAST HAD A VERY GOOD HANDLE ON THINGS...SO WILL ONLY
ADJUST FORECAST FOR LATEST TRENDS. IF PRECIPITATION CHANGES OVER
MORE QUICKLY OR THE HEAVIEST BAND OF SNOW LINGERS A BIT LONGER
SOUTH OF CURRENT HEADLINE AREA...ADVISORY MAY BE NEEDED FROM KRAP
TO KPHP...BUT WILL WAIT TO SEE HOW SYSTEM UNFOLDS.

&&

.SHORT TERM...THIS EVENING THROUGH TUESDAY NIGHT
ISSUED AT 235 PM MDT MON MAR 10 2014

NW CONUS UPPER TROUGH ADVANCING EAST WITH PAC MOISTURE
ADVECTING OVER THE REGION AHEAD OF THIS FEATURE. THIS UPPER TROUGH
WILL SPLIT OVER THE CENTRAL ROCKIES WITH THE NORTHERN VORT LOBE
ADVANCING ACROSS THE FA TONIGHT AND SUPPORTING RAIN AND SNOW.
IMPRESSIVE COMPACT SHORTWAVE TROUGH EXPECTED INTO THE AREA
TONIGHT...WITH STEEP MID LAPSE RATES AND STRONG MOISTURE CONVERGENCE
AND LIFT. PREVIOUS FORECAST PRETTY MUCH ON TRACK WITH THE BIGGEST
ISSUE PER THIS SYSTEM BEING THE TIMING OF WHEN PRECIP WILL SWITCH TO
SNOW. A PERIOD OF COMBINED STRONG LSA AND LL CONVERGENCE IS EXPECTED
SUPPORTING A PERIOD OF DECENT SNOW ACCUMS...ESP IN THE NORTHERN
BLACK HILLS. NORTHERN STREAM UPPER TROUGH WILL DROP SE EAST OF THE
FA SUPPORTING A SECONDARY COLD FRONT INTO THE REGION TUES AFTERNOON.
THIS SYSTEM WILL ALSO BRING GUSTY NW WINDS TO THE SD PLAINS.

TONIGHT...PRIMARY SFC COLD FRONT CONTINUES TO SAG SOUTH IN THE
REGION. HELPING TO ESTABLISHED AN ELEVATED FGEN LAYER ACROSS THE
NORTHERN ZONES AS THE PAC NW COMPACT IMPULSE ADVANCES TOWARD THE
REGION. INCREASING LSA WITH ONGOING MOISTURE ADV ALOFT COUPLED WITH
INCREASED FGEN FORCING WILL LEAD TO EXPANSION OF THE THE RAIN BAND
ACROSS MT INTO NW SD BY EVENING. COLUMNS WILL COOL THROUGH THE
EVENING WITH THE FGEN BAND SLOWLY DRIFTING SOUTH THROUGH THE NIGHT.
DECENT UPGLIDE SIGNAL NOTED IN ISENTROPIC CHARTS WITH 30 KNOTS OF
CROSS ISOBARIC FLOW INDICATED. KEY TO THE SETUP WILL BE STEEP MID
LEVEL LAPSE RATES WITH 7C/KM PROGGED IN THE NAM...STARTING AT THE
BASE OF THE FRONTAL INVERSION AND EXTENDING THROUGH THE DGZ. 50 MB
DEEP DGZ NOTED IN FORECAST MODELS WHICH SHOULD SUPPORT MODERATE
SNOWFALL RATES FOR A PERIOD OF TIME...ESP IN THE 09-12Z PERIOD
ACROSS THE NORTHERN HILLS...GIVEN PW VALUES IN THE 0.6-0.7 INCH
RANGE. TIMING OF PRECIP SWITCH OVER IS AND REMAINS DIFFICULT WITH
A SLIGHTLY EARLY SWITCH OVER FORECAST GIVEN CONCERNS ON STRONG
DYNAMIC LIFT/COOLING. NE PORTIONS OF THE BH AROUND THE
LEAD/DEADWOOD AREA WILL BE IN A PRIME LOCATION FOR UPSLOPE
ENHANCEMENT GIVEN DEEP NE FLOW EVENTUALLY EXTENDING INTO THE DGZ
BY EARLY MORNING WITH COLUMN COOLING. THIS COUPLED WITH EARLIER
SWITCH OVER /PER ELEVATION/IS EXPECTED TO SUPPORT WARNING SNOWS
THERE...EXTENDING NW INTO THE BEAR LODGE MOUNTAINS. WILL UPGRADE
TO A WARNING THERE. DECIDED TO ISSUE AN WW ADV OVER NE WY INTO THE
SD PLAINS FOR 2-4 INCHES OF SNOW WHERE AN FGEN BAND WILL SUPPORT A
PERIOD OF MODERATE SNOWFALL RATES.. WILL ALSO ISSUE A WW ADV FOR
2-4 INCHES ACROSS THE CENTRAL BLACK HILLS WHERE ELEVATION WILL
WILL ALLOW HIGHER SNOW TOTALS. GUSTY NORTHERLY WINDS ARE ALSO
EXPECTED ON THE WY PLAINS GIVEN A SHARP PRESSURE RISE SIGNAL EARLY
TUE MORNING. THIS MAY LEAD TO SOME DRIFTING BLOWING/DRIFTING FOR A
PERIOD TIME.

SNOW WILL CONTINUE INTO TUE MORNING...ENDING BY LATE MORNING AS THE
SYSTEM QUICKLY EXITS THE REGION. TEMPS ARE EXPECTED TO RISE INTO THE
30 AND LOWER 40S MOST PLACES GIVEN STRONG BL MIXING PER CAA/STEEP LL
LAPSE RATES AND A SECONDARY COLD FRONT. HAVE ADJUSTED WINDS FOR
THIS. WINDS ARE NOT EXPECTED TO CAUSE ANY BLOWING SNOW CONCERNS TUE
GIVEN FAIRLY WARM BL TEMPS. GENERALLY COLD CONDITIONS EXPECTED TUE
NIGHT ALTHOUGH WINDS WILL REMAIN UP THROUGH THE NIGHT MOST PLACES
AND ARE EXPECTED TO MODERATE TEMPS TO A DEGREE. SMALL ADJUSTMENT MADE
TO TEMPS.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY
ISSUED AT 235 PM MDT MON MAR 10 2014

UPPER RIDGING ACROSS THE WESTERN CONUS WILL BRING DRY CONDITIONS
AND ABOVE AVERAGE TEMPERATURES THROUGH FRIDAY. THE NEXT SHORTWAVE
DIVES THRU THE NORTHERN PLAINS IN NWRLY FLOW FOR FRIDAY NIGHT AND
THE UPCOMING WEEKEND...BRINGING CHANCES FOR RAIN/SNOW AND SLIGHTLY
COOLER TEMPERATURES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1115 PM MDT MON MAR 10 2014

RASN WILL CHANGE TO SN OVERNIGHT AS IT SPREADS ACROSS THE ENTIRE
AREA THROUGH TUESDAY MORNING WITH IFR CIGS/VSBYS. CONDITIONS
WILL IMPROVE TUESDAY AFTERNOON.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MDT TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MDT TUESDAY FOR SDZ001-002-
     012>014-028-072-073.

WY...WINTER STORM WARNING UNTIL NOON MDT TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL NOON MDT TUESDAY FOR WYZ054-056-
     071.

&&

UPDATE...HELGESON
SHORT TERM...JC
LONG TERM...15
AVIATION...HELGESON

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE RAPID CITY SD
319 PM MDT MON MAR 10 2014

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-111300-
HARDING-PERKINS-BUTTE-NORTHERN MEADE CO PLAINS-ZIEBACH-
NORTHERN BLACK HILLS-NORTHERN FOOT HILLS-RAPID CITY-
SOUTHERN FOOT HILLS-CENTRAL BLACK HILLS-SOUTHERN BLACK HILLS-
CUSTER CO PLAINS-PENNINGTON CO PLAINS-HAAKON-FALL RIVER-SHANNON-
JACKSON-BENNETT-MELLETTE-TODD-TRIPP-STURGIS/PIEDMONT FOOT HILLS-
SOUTHERN MEADE CO PLAINS-HERMOSA FOOT HILLS-NORTHERN CAMPBELL-
SOUTHERN CAMPBELL-WESTERN CROOK-WYOMING BLACK HILLS-WESTON-
NORTHEASTERN CROOK-
319 PM MDT MON MAR 10 2014 /419 PM CDT MON MAR 10 2014/

...WINTER STORM WARNING FROM MIDNIGHT TONIGHT THROUGH TUESDAY
MORNING NORTHERN BLACK HILLS...

...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT THROUGH TUESDAY
MORNING CENTRAL BLACK HILLS AND NORTHEAST WYOMING THROUGH
NORTHWEST SOUTH DAKOTA PLAINS...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN SOUTH DAKOTA AND
NORTHEASTERN WYOMING.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A STRONG LOW PRESSURE SYSTEM WILL MOVE INTO THE AREA TONIGHT. THIS
WILL BRING WIDESPREAD RAIN TO THE REGION...WITH RAIN CHANGING TO
SNOW LATER TONIGHT. SEVERAL INCHES OF SNOW ACCUMULATION IS
EXPECTED...WITH MORE THAN 6 INCHES IN THE NORTHERN BLACK HILLS
AND NORTHERN FOOTHILLS. LESSER AMOUNTS ARE EXPECTED ON THE PLAINS
OF NORTHEAST WYOMING AND WESTERN SOUTH DAKOTA WHERE 2 TO 4 INCHES
IS EXPECTED.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

SNOW WILL CONTINUE TUESDAY MORNING...THEN END TUESDAY AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY.

&&

STAY TUNED TO NOAA WEATHER RADIO FOR FURTHER DETAILS OR UPDATES...
OR CHECK OUR WEB SITE AT WEATHER.GOV/RAPIDCITY

JC