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000
FXUS63 KUNR 180839
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
239 AM MDT SAT MAY 18 2013

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 237 AM MDT SAT MAY 18 2013

08Z THE MOST INTENSE LINGERING CONVECTION IS MOSTLY
ALONG AND SOUTH OF THE WARM FRONT IN SOUTH CENTRAL SOUTH DAKOTA AND
NORTHWESTERN NEBRASKA.  THE FRONT STRETCHES FROM SOUTHWEST SOUTH
DAKOTA NORTHEASTWARD INTO NORTH CENTRAL SOUTH DAKOTA. THUNDERSTORM
INTENSITIES HAVE DECREASED TO BELOW SEVERE CRIERIA...BUT BRIEF HEAVY
RAIN SMALL HAIL AND LIGHTNING ARE ALL THREATS FROM THESE
STORMS...ESPECIALLY THE CLUSTER MOVING THROUGH NORTHERN JACKSON
COUNTY...AND THE MEDIUM SIZE MCS MOVING NORTHEAST OUT OF CHERRY
COUNTY NEBRASKA. A SURFACE LOW HAS FORMED ON THE FRONT IN
SOUTHWESTERN SOUTH DAKOTA AS DEPICTED IN THE HPC PROGS.  IN THE WAKE
OF THE LARGE CONVECTIVE COMPLEXES SKIES HAVE CLEARED SIGNIFICANTLY
OVER NORTHEASTERN WYOMING AND SOME OF WESTERN SOUTH DAKOTA. LOCALLY
DENSE FOG HAS FORMED OVER PARTS OF NORTHEAST WYOMING...AND MORE FOG
CAN BE EXPECTED TO DEVELOP IN WESTERN SOUTH DAKOTA AS SKIES CONTINUE
TO CLEAR TO THE EAST THROUGH THE MORNING HOURS.

TODAY AND TONIGHT...THE PREVIOUS LARGE SCALE SENARIO DESCRIPTION IS STILL
ON TRACK WITH THE NORTHERN MOST OF THE TWO WEAK SURFACE LOWS NOW IN
SOUTHWESTERN SOUTH DAKOTA AND DRIFTING NORTHEASTWARD. THIS IS LIKELY
TO DEVELOP A SHARP KINK IN THE FRONT EARLY THIS MORNING...SETTING UP
A NORTH/SOUTH BOUNDARY IN THE EASTERN PART OF THE UNR CWA BY MIDDAY.
THIS BOUNDAY SHOULD SERVE AS THE FOCUS FOR THE FIRST ROUND OF
CONVECTION WHILE SKIES ARE STILL MOSTLY SUNNY THROUGH EARLY
AFTERNOON.  BY LATER IN THE DAY THE UPPER LEVEL DYNAMICS ASSOCIATED
WITH THE MAIN BODY OF THE PACIFIC TROUGH WILL DETERMINE WHERE THE
LARGEST CLUSTERS OF THUNDERSTORMS DEVELOP FOR THE REMAINDER OF THE
EVENT.  MODEL SOUNDINGS SHOW A VERY MOIST AIRMASS WITH PLENTY OF
INSTABILITY AND SHEAR FOR SUPERCELLS...ESPECIALLY NEAR THE FRONT.
MCS DEVELOPMENT IS LIKELY AS THE MAIN VORTICITY CENTER MOVES ACROSS
WESTERN SOUTH DAKOTA SATURDAY EVENING. A FEW SPOTS RECIEVED SEVERAL
INCHES OF RAIN FRIDAY EVENING AND WILL NEED TO BE MONITORED FOR
FLASH FLOOD POTENTIAL THIS AFTERNOON.

SUNDAY...PRECIPITATION PRODUCTION WILL SWITCH OVER MOSTLY TO
ISENTROPIC PROCESSES AS THE SURFACE TROUGH MOVES INTO THE EASTERN
DAKOTAS DURING THE OVERNIGHT HOURS EARLY SUNDAY MORNING. SHEAR AND
INSTABILITY ARE EXPECTED TO DECREASE SIGNIFICANTLY IN THE SATURATED
AIRMASS AS THE WRAP AROUND CONVEYOR SETS UP FOR THE HIGH PLAINS.
THE POTENTIAL FOR A SLOW GENTLE RAIN EVENT FOR MOST AREAS ON SUNDAY
IS APPEALING AS DROUGHT CONDITIONS HAVE ONLY IMPROVED A LITTLE.
MAXIMUM TEMPERATURES WILL TOP OUT IN THE 60S IN THE COOL PACIFIC
AIRMASS ACCOMPANYING THE TROUGH.

&&

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 237 AM MDT SAT MAY 18 2013


MEDIUM RANGE MODELS REMAIN IN GENERAL AGREEMENT WITH PROGRESSION AND
TRACK OF UPPER LOW EARLY NEXT WEEK...BUT CONTINUE TO TREND THE
SYSTEM A BIT FURTHER SOUTH WITH EACH MODEL RUN. WITH THE LOW STILL
PROJECTED TO STALL OUT ACROSS THE SOUTHEASTERN SD AREA MONDAY INTO
TUESDAY...PLENTY OF WRAP AROUND RAINFALL CAN BE EXPECTED ACROSS MUCH
OF THE FORECAST AREA. THE LATEST CONSENSUS WOULD STILL BRING
SIGNIFICANT RAINFALL TO THE AREA...WITH SOUTHERN SD POTENTIALLY
RECEIVING THE HIGHEST AMOUNTS AND FAR NORTHERN PORTIONS OF NW SD
INTO NORTHEASTERN WY POSSIBLY SEEING A BIT LESS RAINFALL. THERE IS
STILL PLENTY OF UNCERTAINTY AT THIS POINT...BUT 1 TO 2 INCHES OF
RAIN SHOULD BE COMMON ACROSS THE AREA FROM LATER SUNDAY INTO
TUESDAY...WITH SOME HIGHER AMOUNTS LIKELY ACROSS SOUTHERN
SD...ESPECIALLY TOWARD SOUTH CENTRAL SD. WILL KEEP LIKELY TO
CATEGORICAL POPS ACROSS THE AREA MONDAY AND MONDAY NIGHT. THERE
STILL LOOKS TO BE SOME POTENTIAL FOR SNOW ACROSS THE HIGHEST
ELEVATIONS OF THE BLACK HILLS LATE MONDAY NIGHT/EARLY TUESDAY...BUT
WILL LEAVE OUT POSSIBILITY UNTIL THE FORECAST BECOMES MORE CLEAR.
COOL AND BREEZY/WINDY CONDITIONS CAN BE EXPECTED MONDAY AND
TUESDAY...WITH HIGHS IN THE 50S AND LOWER 60S.

AT THIS POINT...IT STILL LOOKS THE SYSTEM WILL EJECT EASTWARD OUT OF
THE REGION LATER TUESDAY AND TUESDAY NIGHT...WITH GRADUALLY
IMPROVING CONDITIONS FROM WEST TO EAST. BEYOND TUESDAY...THERE
SHOULD BE A GRADUAL WARMUP FOR THE MIDDLE INTO THE LATTER PART OF
THE WEEK...ESPECIALLY ACROSS WESTERN AREAS...AS A WEAK RIDGE PASSES
THROUGH THE PLAINS. WILL GO WITH A MAINLY DRY FORECAST FOR WEDNESDAY
INTO THURSDAY AS THE RIDGE PASSES. SOUTHWEST FLOW ALOFT WILL DEVELOP
AGAIN BY THE END OF THE WEEK...SO WILL SEE CHANCES FOR SHOWERS AND
THUNDERSTORMS INCREASE THURSDAY NIGHT INTO NEXT WEEKEND.

&&

.AVIATION...FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT
ISSUED AT 237 AM MDT SAT MAY 18 2013

SHOWERS AND THUNDERSTORMS ACROSS FAR EASTERN PORTIONS OF THE CWA
WILL TRACK OUT OF THE AREA EARLY THIS MORNING. ONLY ISOLATED SHOWER
ACTIVITY IS THEN EXPECTED THROUGH THE REST OF THE MORNING...MAINLY
ACROSS NORTHEASTERN WY...THE BLACK HILLS...AND NORTHWESTERN SD. LOW
CLOUDS AND PATCHY FOG HAVE DEVELOPED ACROSS AREAS ON THE PLAINS...
ESPECIALLY NORTHEASTERN WY AND FAR WESTERN SD...WITH IFR AND LOCAL
LIFR CONDITIONS. MORE WIDESPREAD THUNDERSTORM ACTIVITY WILL DEVELOP
THIS AFTERNOON AND CONTINUE INTO TONIGHT...WITH SEVERE THUNDERSTORMS
EXPECTED THIS AFTERNOON AND EVENING FROM THE BLACK HILLS EASTWARD.

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

$$

SHORT TERM...CARPENTER
LONG TERM...26
AVIATION...26