000
FXUS63 KUNR 181748
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1148 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 CRITERIA...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 SCENARIO 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 BOUNDARY 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 RECEIVED 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 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1142 AM MDT SAT MAY 18 2013

LOW STRATUS WILL PERSIST ACROSS AREAS OF THE PLAINS THROUGH MID
AFTERNOON...ESPECIALLY NORTHEASTERN WYOMING AND SOUTHERN PORTIONS
OF SD...WITH MVFR AND LOCAL IFR CEILINGS. SHOWERS AND
THUNDERSTORMS WILL DEVELOP THIS AFTERNOON AND CONTINUE INTO
TONIGHT...WITH SEVERE THUNDERSTORMS EXPECTED THROUGH THIS EVENING
FROM THE BLACK HILLS EASTWARD. IFR AND LIFR CEILINGS WITH RAIN
WILL SET INTO NORTHEAST WYOMING AFTER MIDNIGHT.

&&

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

$$

SHORT TERM...CARPENTER
LONG TERM...26
AVIATION...15