496 FXUS63 KFSD 172332 AFDFSD AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 632 PM CDT MON JUL 16 2012 .DISCUSSION.../ISSUED AT 407 PM CDT/ A HOT AND HUMID DAY CURRENTLY UNDERWAY WITH TEMPERATURES WELL INTO THE 90S AND DEWPOINTS IN THE 60S. FRONTAL BOUNDARY CURRENTLY SITUATED AROUND HIGHWAY 14...SHOULD SLOWLY MOVE SOUTH THIS EVENING. ATMOSPHERE REMAINS CAPPED OVER THE AREA...DESPITE MLCAPE OVER 3500 J/KG NORTH OF THE BOUNDARY. INTERESTINGLY...CU HAS FORMED FURTHER SOUTHWEST ACROSS NEBRASKA AND NEAR THE MISSOURI RIVER. IT SEEMS LIKELY THE ATMOSPHERE HAS MIXED ALL THE WAY THROUGH THE CAP IN THESE AREAS. THIS IS EVIDENT BY THE LOWER DEWPOINTS IN THE 40S AND 50S IN THESE AREAS. SO WHILE THIS MIXING HAS ERODED THE CAP...IT HAS ALSO ERODED MUCH OF THE INSTABILITY...HENCE THE LACK OF OF SIGNIFICANT UPGROWTH. EXPECT THIS TO CONTINUE TO BE THE CASE THROUGH THE EVENING WITH ONLY AN ISOLATED SHOWER OR THUNDERSTORM WITH THAT CU. SEEMS MORE PROBABLE THAT CONVECTION DEVELOPS WEST OF OUR CWA ALONG THE OTHER BOUNDARY. THESE STORMS SHOULD PROPAGATE TOWARDS OUR WESTERN CWA THIS EVENING...POSSIBLY IMPACTING LOCATIONS WEST OF THE JAMES RIVER. WILL ALSO HAVE TO MONITOR DEVELOPMENT ALONG THE BACKDOOR BOUNDARY AS IT DROPS SOUTH THROUGH THE CWA. HRRR AND NAM SEEM TO BE OVERDOING CONVECTION CHANCES WITH THIS BOUNDARY...BUT CANT RULE OUT A FEW STORMS WITH ABUNDANT LOW LEVEL MOISTURE POOLING AROUND THE BOUNDARY. UPPER LEVEL FORCING AND DEEPER MOISTURE SHOULD MOVE ACROSS THE CWA AFTER MIDNIGHT TONIGHT. SO EVEN IF NO SURFACE CONVECTION GETS GOING THIS EVENING...SHOULD HAVE A CHANCE OF ELEVATED STORMS LATER TONIGHT NORTH OF THE BOUNDARY IN AREA OF LOW LEVEL THETAE ADVECTION. THIS CONVECTION WILL LIKELY STAY GENERALLY FROM HIGHWAY 34 AND POINTS NORTH...WITH THE ECMWF ACTUALLY KEEPING IT NORTH OF THE CWA...SO DID NOT GO ANY HIGHER THAT 30 TO 40 POPS. LOWS TONIGHT WILL STAY MILD...GENERALLY LOW TO MID 70S. WEDNESDAY WILL BE ANOTHER HOT ONE ACROSS MUCH OF THE REGION...WITH HIGHS IN THE 90S EVERYWHERE BUT SOUTHWEST MINNESOTA. DEWPOINTS WILL LIKELY BE HIGHER THAN TODAY...ESPECIALLY ALONG AND EAST OF INTERSTATE 29...WHERE VALUES IN THE LOW 70S ARE LIKELY. THIS WILL MAKE FOR ANOTHER DAY OF VERY HIGH HEAT INDICES...SO WENT AHEAD AND ISSUED A HEAT ADVISORY FOR AREAS MOST LIKELY TO HAVE A HEAT INDEX OVER 100. THE ABOVE MENTIONED WAVE WILL CONTINUE TO PUSH EAST WEDNESDAY. BY THIS TIME BEST CHANCE OF CONVECTION SHOULD BE GENERALLY EAST OF INTERSTATE 29. AREAS TO THE WEST WILL BE UNDER AN AREA OF LARGE SCALE SUBSIDENCE AND SHOULD REMAIN CAPPED. INITIAL CONVECTION SHOULD EB ELEVATED...BUT IF THE WAVE MOVES SLOW ENOUGH WE SHOULD SEE A TRANSITION TO SURFACE BASED CONVECTION BY AFTERNOON. IF THIS HAPPENS...WOULD BE MOST LIKELY OVER SOUTHWEST MINNESOTA AND PORTIONS OF NORTHWEST IOWA. COULD SEE A COUPLE SEVERE STORMS DURING THE AFTERNOON...WITH A BIT BETTER SHEAR EXPECTED. /CHENARD ANY CONVECTION THAT DEVELOPS ON WEDNESDAY AFTERNOON MAY LINGER INTO THE EVENING ACROSS NW IOWA AND SW MN. MODELS DO SHOW A SECOND WEAK WAVE MOVING SOUTHEAST ACROSS MINNESOTA ON WEDNESDAY NIGHT. THIS MAY RESULT IN MORE STORMS DEVELOPING INTO SOUTHWEST MINNESOTA AFTER SUNSET. AGAIN...ANY STORM DEVELOPMENT WILL BE SOMEWHAT ISOLATED. ANY STORMS SHOULD MOVE EAST BY DAWN ON THURSDAY. OTHERWISE...EASTERLY FLOW IS EXPECTED ACROSS THE AREA THROUGH THE EVENING. THIS WILL BRING A BIT COOLER AIR INTO THE AREA...ALLOWING LOWS TO DROP BELOW 70 DEGREES IN SW MN ANAD BETWEEN 70 AND 75 DEGREES ELSEWHERE. THE UPPER LEVEL RIDGE WILL BUILD ACROSS THE AREA THURSDAY AND FRIDAY. AS HEIGHTS RISE AT 500 MB...THE SURFACE RIDGE WILL STRENGTHEN OVER THE GREAT LAKES. THIS WILL KEEP WINDS OUT OF THE EAST DURING THE DAY. HOWEVER...MOSTLY SUNNY SKIES ARE EXPECTED AND THE AIR MASS REMAINS VERY WARM. TEMPERATURES ARE EXPECTED TO BE SIMILAR TO WEDNESDAY FROM AROUND 90 IN SOUTHWEST MINNESOTA TO AROUND 100 IN SOUTH CENTRAL SD. CLEAR SKIES AND RELTIAVELY LIGHT WINDS ARE AGAIN EXPECTED THURSDAY NIGHT. LOWS WILL BE SIMLAR TO WEDNESDAY NIGHT FROM THE UPPER 60S IN SOUTHWEST MINNESOTA TO 70 TO 75 ELSEWHERE. THE REMAINDER OF THE FORECAST WILL REALLY FOCUS ON THE RETURN OF THE HEAT. OVERALL...THE GFS AND ECMWF ARE VERY SIMILAR ON THE STRENGTH AND DURATION OF THIS RIDGE. BY EARLY NEXT WEEK THEY BOTH HAVE A FAIRLY STRONG WAVE MOVE ALONG THE CANADIAN BORDER. THEY ALSO SHOW THE RIDGE VERY SLOWLY BREAKING DOWN BY TUESDAY OR WEDNESDAY ALTHOUGH OVERALL THE RIDGE REMAINS OVER THE CENTRAL UNITED STATES THROUGH THE MIDDLE NEXT WEEK SO NO SIGNIFICANT BREAK IN THE HEAT IS REALLY EXPECTED FOR THE NEXT 7 DAYS. IN TERMS OF PRECIPITATION...BOTH MODELS SHOW A WEAK SYSTEM MOVING ACROSS THE DAKOTAS ON SUNDAY BUT IT REMAINS VERY WARM ALOFT OVER SOUTHERN SOUTH DAKOTA AND THE LARGE SCALE FORCING FOR ASCENT REMAIN CLOSER TO THE CANADIAN BORDER. SO WHILE WE HAVE KEPT A 20 TO 30 PERCENT CHANCE OF PRECIPATION FOR SUNDAY AND SUNDAY NIGHT...THE CONVECTION DOES NOT LOOK TO BE WIDESPREAD AT THIS POINT AND MOST AREAS WILL LIKELY NOT SEE ANY RAIN FROM THIS SYSTEM. GOING INTO NEXT WEEK...THERE DOES NOT APPEAR TO BE ANY REAL CHANCE OF WIDESPREAD RAINFALL INTO THE MIDDLE OF NEXT WEEK. LOOKING AT DAY TO DAY...FRIDAY WILL SEE THE HEAT SPREAD INTO THE JAMES VALLEY WITH HIGHS AROUND 100. TO THE EAST HIGHS WILL RANGE FROM THE LOWER 90S AROUND HIGHWAY 71 IN MINNESOTA AND IOWA...TO THE MID TO UPPER 90S IN THE REMAINDER OF SOUTHEAST SOUTH DAKOTA. AFTER FRIDAY...LOWS SATURDAY MORNING THROUGH TUESDAY MORNING WILL BE IN THE LOWER TO MID 70S. HIGHS ON SATURDAY AND SUNDAY WILL BE SIMILAR TO FRIDAY GENERALLY IN THE LOWER 90S IN SOUTHEAST MINNESOTA TO AT OR ABOVE 100 WEST OF THE JAMES RIVER. IF THERE ARE LESS CLOUDS OR THE SURFACE HIGH RETREATS MORE QUICKLY...TEMPERATURES BOTH DAYS COULD BE 2 TO 5 DEGREES WARMER...RESULTING IN HIGHS APPROACHING 100 OVER MUCH OF THE AREA. A WEAK BOUNDARY WILL GO THROUGH SUNDAY EVENING AND THIS MAY BRING A BIT COOLER AIR INTO THE AREA. HOWEVER...HOW COOL THE AIR WILL BE AND HOW LONG IT REMAINS IS VERY UNCERTAIN AT THIS POINT. FOR NOW...FORECAST HIGHS ONLY 3 TO 5 DEGREES COOLER THAN THE WEEKEND WHICH MEANS 90S LOOK TO PERSIST THROUGH TUESDAY. IF THE FRONT RETREATS BACK TO THE NORTH MORE QUICKLY...PER THE 12Z ECMWF...HIGHS COULD BE BACK OVER 100 DEGREES IN PARTS OF THE AREA BY TUESDAY./SCHUMACHER && .AVIATION.../FOR THE 00Z TAF ISSUANCE/ MAINLY VFR CONDITIONS ARE EXPECTED THROUGH 00Z THURSDAY. FRONT SLOWLY PROGRESSING SOUTH ACROSS THE CWA AT THIS TIME. ISOLATED SURFACE BASED CONVECTION DEVELOPING ACROSS THE AREA...BUT CONFIDENCE IN IT REACHING ANY OF THE PARTICULAR AIRPORTS LOW ENOUGH THAT IT WAS LEFT OUT OF THE FORECAST. THERE IS SOME ELEVATED CONVERGENCE TONIGHT WITH THE I-90 CORRIDOR LOCATED ON THE NOSE OF THE LOW LEVEL JET. POTENTIAL FOR STORMS TO AFFECT I-90 AND HIGHWAY 14 CORRIDOR BUT AGAIN CONFIDENCE IS TOO LOW TO INCLUDE IN THE FORECAST. SMALL CHANCE A FEW OF THESE STORMS FORM FURTHER SOUTH WEDNESDAY MORNING AND EARLY AFTERNOON CLOSER TO KFSD AND KSUX...BUT PROBABILITY AND TIMING CONFIDENCE TOO LOW TO INCLUDE IN TAF. MODEL SOUNDINGS ARE QUICK TO GO CONVECTIVE...BUT APPEAR TO BE TOO QUICK TO BREAK DOWN THE ELEVATED INVERSION ALOFT. IF CONVECTION WAS ABLE TO DEVELOP BEST CHANCES WOULD BE IN THE 17-21Z TIMEFRAME FOR INITIATION. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && $$