Heavy Snow in Wyoming, February 22 to 23, 2012

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1022 PM MST TUE FEB 21 2012

.AVIATION...06Z TAFS
MAINLY VFR CONDITIONS AND CIGS FROM 4-8KFT ARE EXPECTED ON THE SD
PLAINS THROUGH WEDNESDAY AFTERNOON...BUT NORTHWEST WINDS WILL
RAPIDLY INCREASE BY MIDDAY WEDNESDAY WITH GUSTS TO 40KTS AT TIMES.
LOCALIZED MVFR CIGS NEAR PRECIPITATION POSSIBLE AT TIMES. OVER
NORTHEASTERN WY AND THE BLACK HILLS...PRECIPITATION WILL CONTINUE
INTO WEDNESDAY...ESPECIALLY OVER THE HIGHER TERRAIN. FREQUENT
MVFR/IFR CIGS/VSBYS ARE FORESEEN IN THE STRONGEST AREAS OF -RASN.

&&

.PREV DISCUSSION... /ISSUED 842 PM MST TUE FEB 21 2012/

DISCUSSION...03Z SURFACE ANALYSIS HAD TROUGH FROM SOUTHERN SK
INTO EASTERN NE. 00Z KUNR SOUNDING SHOWED STEEP LOW LEVEL LAPSE
RATES...WITH DRY AIR BELOW 700MB. WATER VAPOUR HAD 130KT JET
NOSING INTO MT/WY WITH LEFT EXIT REGION PROVIDING NOTABLE LIFT
OVER THE CWA PER MODEL ANALYSIS. INITIAL WAVE OVER SOUTHWEST ND
BRINGING RADAR RETURNS OVER MUCH OF THE CWA...REACHING THE GROUND
IN SOME SPOTS ESPECIALLY IN THE HIGHER TERRAIN. CALLS TO SPOTTERS
INDICATED ABOUT AN INCH OF NEW SNOW OVER THE NORTHERN BLACK
HILLS/WY BLACK HILLS.

OVERNIGHT INTO WEDNESDAY MORNING...EXPECT ANOTHER WAVE TO DROP
DOWN FROM CANADA UNDER LEFT EXIT REGION OF JET. ANOTHER ROUND OF
ENHANCED FORCING EXPECTED AND THUS HAVE INCREASED POPS SOME AND
EXPANDED LIKELY POPS OVER A LARGER AREA. STEEP LAPSE RATES WILL
SUPPORT CONVECTIVE ELEMENTS AT TIMES AND HAVE BUMPED UP SNOW
AMOUNTS SOME IN THE HIGHEST ELEVATIONS.

LOOKING AT POTENTIAL WIND EVENT FOR WEDNESDAY AFTERNOON...LATEST
GUIDANCE SHOWS LESSER WIND SPEEDS...BUT ADVISORY STILL LOOKS GOOD.

PREV DISCUSSION... /ISSUED 211 PM MST TUE FEB 21 2012/

DISCUSSION...LONG WAVE RIDGE IS JUST OFF THE WEST COAST WITH LONG
WAVE TROF NEAR 100W THIS MORNING. MID TROPOSPHERIC FLOW IS FROM
THE NORTHWEST OVER OUR CWA AND WILL BE STRENGTHENING AS RIDGE
BUILDS TO THE WEST.

NEAR SURFACE PRESSURE GRADIENTS WILL INCREASE ACROSS THE
CWA LATE TONIGHT AND WEDNESDAY MORNING WITH ADVISORY LEVEL SFC
WINDS DEVELOPING WEDNESDAY. 12Z NAM PUSHES A COLD FRONT SOUTHWARD
ACROSS THE CWA AFTER 00Z TOMORROW EVENING FOLLOWED BY A SMALL
AREA OF STRONG PRESSURE RISES MOVING FROM SE MT SE WARD ACROSS THE
CWA. SFC WINDS OVER THE SOUTH DAKOTA PLAINS WILL REMAIN NEAR OR
ABOVE ADVISORY CRITERIA WITH THIS ISALLOBARIC BOAST DURING THE
OVERNIGHT HOURS.

MOST PRECIP WILL BE CONFINED TO THE BLACK HILLS UP SLOPE AREAS
TONIGHT AND EARLY WEDNESDAY WITH SOME CHANCE OF SHOWERS ELSEWHERE
OVER THE CWA. LATTER ARE SUPPORTED BY WEAK...SHORT WAVE LENGTH
AREAS OF Q-VECTOR CONVERGENCE PASSING OVER THE AREA. MORE LIKELY
CHANCES ARE SHOWN BY MESO MODELS ACCOMPANYING AND FOLLOWING COLD
FROPA LATE THURSDAY NIGHT.

ON THURSDAY...REGION REMAINS IN ACTIVE PATTERN AS SECONDARY WAVE
SLIDES THROUGH AND COOLER AIRMASS SHIFTS INTO THE REGION. ANOTHER
DAY OF GUSTY WINDS IS AGAIN EXPECTED AS MODELS CONTINUE TO ADVERTISE
40-50 KT 850MB WINDS MIXING DOWN...WITH THE STRONGEST WINDS OVER THE
SODAK PLNS. FROUDE ANALYSIS CONTINUES TO SUGGEST UPSLOPE ENHANCEMENT
THROUGH THE DAY...SO WILL KEEP HIGHER POPS OVER NRN BLKHLS...WITH
CHANCE POPS OVER MOST REMAINING LOCATIONS.

EXTENDED...A TRANSIENT UPPER LEVEL RIDGE WILL CROSS THE NRN PLAINS
FRIDAY NIGHT AND SATURDAY...WHICH SHOULD BRING A BRIEF RESPITE FROM
PCPN CHANCES...ALONG WITH WARM ADVECTION. BEGINNING SATURDAY...THE
MODELS CONTINUE TO SHOW DIVERGING SOLUTIONS AS THE NEXT UPPER TROUGH
WORKS INTO THE WRN CONUS. THE ECMWF HAS BEEN SLOW WITH THE MAIN
TROUGH RELATIVE TO THE GFS...AND THE CANADIAN HAS SUPPORTED THE
SLOWER ECMWF. AS A RESULT...EXPECT FROPA TO BE ON SUNDAY INSTEAD OF
SATURDAY. IN ADDITION...ARCTIC AIR SHOULD BE ENTRENCHED OVER THE
AREA LATE SUNDAY AND MONDAY...WHICH WILL HELP TO SQUEEZE OUT SOME
LIGHT SNOW. THERE IS THE POTENTIAL FOR A DECENT STORM TO DEVELOP AS
THIS PATTERN CHANGE OCCURS...BUT THE MOST LIKELY SCENARIO APPEARS TO
HAVE IT DEVELOP NORTH AND EAST OF OUR CWA. HOWEVER...BELOW AVERAGE
TEMPERATURES SHOULD RULE FOR MOST OF NEXT WEEK.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY FROM 11 AM MST /NOON CST/ WEDNESDAY TO 6 PM MST /7
     PM CST/ THURSDAY FOR BENNETT-CUSTER CO PLAINS-FALL RIVER-
     HAAKON-HERMOSA FOOT HILLS-JACKSON-MELLETTE-SHANNON-SOUTHERN
     FOOT HILLS-TODD-TRIPP-ZIEBACH.

     WIND ADVISORY FROM 11 AM WEDNESDAY TO 8 AM MST THURSDAY FOR
     BUTTE-HARDING-NORTHERN FOOT HILLS-NORTHERN MEADE CO PLAINS-
     PENNINGTON CO PLAINS-PERKINS-RAPID CITY-SOUTHERN MEADE CO
     PLAINS-STURGIS/PIEDMONT FOOT HILLS.

     HIGH WIND WATCH FROM THURSDAY MORNING THROUGH THURSDAY AFTERNOON
     FOR BUTTE-HARDING-NORTHERN FOOT HILLS-NORTHERN MEADE CO
     PLAINS-PENNINGTON CO PLAINS-PERKINS-RAPID CITY-SOUTHERN
     MEADE CO PLAINS-STURGIS/PIEDMONT FOOT HILLS.

WY...NONE.
&&

SHORT TERM...WFO UNR
LONG TERM....WFO UNR
AVIATION...HELGESON

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RAPID CITY SD
356 AM MST TUE FEB 21 2012

SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058-
071-221400-
BENNETT-BUTTE-CENTRAL BLACK HILLS-CUSTER CO PLAINS-FALL RIVER-HAAKON-
HARDING-HERMOSA FOOT HILLS-JACKSON-MELLETTE-NORTHEASTERN CROOK-
NORTHERN BLACK HILLS-NORTHERN CAMPBELL-NORTHERN FOOT HILLS-
NORTHERN MEADE CO PLAINS-PENNINGTON CO PLAINS-PERKINS-RAPID CITY-
SHANNON-SOUTHERN BLACK HILLS-SOUTHERN CAMPBELL-SOUTHERN FOOT HILLS-
SOUTHERN MEADE CO PLAINS-STURGIS/PIEDMONT FOOT HILLS-TODD-TRIPP-
WESTERN CROOK-WESTON-WYOMING BLACK HILLS-ZIEBACH-
356 AM MST (456 AM CST) TUE FEB 21 2012

...HIGH WIND WATCH FOR WEDNESDAY ACROSS THE PLAINS OF NORTHWEST
   AND WEST CENTRAL SOUTH DAKOTA...

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

.DAY ONE...TODAY AND TONIGHT

AN ACTIVE WEATHER PATTERN WILL BRING CHANCES FOR RAIN AND SNOW
SHOWERS TODAY ACROSS THE NORTHERN BLACK HILLS...AND PARTS OF
NORTHEAST WYOMING AND FAR NORTHWEST SOUTH DAKOTA. BETTER CHANCES
OF PRECIPITATION ARE EXPECTED TONIGHT AS A STRONGER DISTURBANCE
CROSSES THE AREA. SNOW ACCUMULATIONS ARE EXPECTED TO BE AN INCH OR
LESS TODAY...AND ONE TO THREE INCHES POSSIBLE TONIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

A FAST MOVING SYSTEM WILL BRING RAIN AND SNOW TO THE AREA WEDNESDAY.
THIS SYSTEM WILL ALSO BRING GUSTY WEST TO NORTHWEST WINDS TO THE
AREA. WINDS COULD REACH 35 TO 55 MPH WITH GUSTS TO 60 MPH. WINDS ARE
EXPECTED TO DECREASE BY WEDNESDAY EVENING...BUT WILL REMAIN GUSTY
THROUGH WEDNESDAY NIGHT AND INTO THURSDAY. SNOW WILL CONTINUE TO FALL
ACROSS THE NORTHERN BLACK HILLS WEDNESDAY THROUGH THURSDAY. AS A
RESULT...LIGHT TO MODERATE SNOW ACCUMULATIONS ARE EXPECTED ALTHOUGH
AMOUNTS ARE UNCERTAIN AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY.