Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 182311
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
511 PM MDT FRI APR 18 2014

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 209 PM MDT FRI APR 18 2014

FAST FLOW OVER THE PACIFIC WILL CONTINUE TO SUPPORT FAIRLY RAPID
EASTWARD MOVEMENT OF THE SHORT WAVE TROF OVER THE PAC NW THIS
MORNING. THIS TROF WILL MOVE TO CENTRAL MT BY 00Z THIS EVENING AND
TO NEAR LAKE WG BY 12Z SAT. SHORT WAVE RIDGE AHEAD OF THIS TROF
WAS LOCATED OVER WRN SD THIS AFTERNOON...EVIDENT IN IR AND WV
SATELLITE PICS WITH COLDER AND MORE CONTINUOUS HIGH CLOUDS TO ITS
WEST AND THIN HIGH CLOUDS STREAMING OVER THE RIDGE INTO OUR CWA.

AS TROF APPROACHES...BEST SUPPORT FOR ASCENT SHOWN BY 700MB Q
VECTOR CONVERGENCE SPLITS INTO TWO AREAS. THE STRONGER MOVES
NORTHEASTWARD AHEAD OF THE TROF ACROSS ND...WHILE A SECOND AREA
DVLPS OVER SOUTHEAST WY AND ELONGATES OVER THE LOW LEVEL BAROCLINIC
ZONE OVER CO...NORTHERN NE...AND EASTERN SD BY 12Z SAT.

LOW LEVEL RESPONSE TO THESE DEVELOPMENTS ALOFT IS MODEST
CYCLOGENESIS OVER NE WY AND WESTERN SD...ONGOING THIS AFTN.
ANALYSES OF SFC GEOSTROPHIC VORTICITY CHANGES REVEAL INCREASING
VALUES OVER THIS AREA THIS AFTN. THESE CHANGES SHOULD SUPPORT
ENHANCED LOW LEVEL CONVERGENCE AND INCREASED CHANCES FOR SHOWER
AND TSTM DEVELOPMENT...THOUGH PROBABILITIES WILL REMAIN LOW. 18Z
NAM AND RECENT RUNS OF THE HRRR MODEL GIVE SUPPORT TO THIS
DEVELOPMENT...THOUGH DETAILS OF STORM LOCATION/INTENSITY HAVE BEEN
VARYING FROM RUN TO RUN OF THE HRRR.

FCST SOUNDINGS INDICATE 500 TO 750 J/KG OF CAPE OVER WRN SD LATE
THIS AFTN INTO EARLY THIS EVG. VERY LIMITED MOISTURE WILL PRECLUDE
SEVERE DEVELOPMENT...BUT INVERTED V SOUNDINGS WITH HIGH LCLS
SUGGEST POTENTIAL FOR A FEW STRONG WIND GUSTS WITH ANY STORMS THAT
DO DEVELOP.

FOLLOWING PASSAGE OF THE COLD FRONT AND NORTH EASTWARD MOVEMENT OF
THE SFC LOW...BRISK NORTHWESTERLY WINDS WILL DEVELOP OVER THE
WHOLE CWA LATE TONIGHT INTO EARLY SAT MORNING WITH COOLER
TEMPERATURES AND DRY WEATHER ON SATURDAY AND SATURDAY NIGHT.



&&

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 209 PM MDT FRI APR 18 2014

THE UPPER LEVEL THERMAL RIDGE WILL SHIFT OFF TO THE
EAST SUNDAY AFTN AS AN UPPER TROUGH CROSSES NORTH DAKOTA AND SWINGS
A COOL FRONT ACROSS THE FORECAST AREA. WEAK INSTABILITY DEVELOPS
OVER WESTERN SOUTH DAKOTA AHEAD OF THE FRONT ON SUNDAY AFTERNOON.
HOWEVER DUE TO THE LOW RH OF THE AIRMASS IN PLACE AT THE TIME WILL
LEAVE THE SUN AFTN FORECAST DRY. THE UPPER RIDGE WILL REBOUND
QUICKLY OVER THE NORTHERN PLAINS ON MONDAY WITH WARM AND DRY WEATHER
CONTINUING THROUGH TUESDAY. A STRONG AND SLOW MOVING UPPER LEVEL
TROUGH WILL CREATE CHANCES OF PRECIPITATION FROM TUESDAY NIGHT INTO
FRIDAY. SHRA/TSRA WILL BE POSSIBLE...ESPECIALLY TUESDAY/WEDNESDAY.
MODELS REMAIN IN DECENT AGREEMENT IN PUSHING THE MAIN UPPER
LOW/SHORTWAVE ASSOCIATED WITH UPPER TROUGH NORTH OF CWA...WHICH
WOULD RESULT IN A MOSTLY LIQUID EVENT. CAN/T RULE OUT SOME SLUSHY
SNOW THURSDAY NIGHT...BUT MOISTURE AVAILABILITY BEHIND SYSTEM IN
QUESTION.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING
ISSUED AT 508 PM MDT FRI APR 18 2014

GUSTY NORTHWESTERLY WINDS ARE EXPECTED BEHIND A COLD
FRONT THIS EVENING...ESPECIALLY ACROSS THE SOUTH DAKOTA PLAINS. VFR
CONDITIONS WILL PREVAIL ACROSS MOST AREAS. THERE IS A CHANCE OF
TSRA THIS EVENING WITH LOCALIZED MVFR VSBYS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

SHORT TERM...BARBER
LONG TERM...10
AVIATION...POJORLIE





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