Issued by NWS Sioux Falls, SD
000 FXUS63 KFSD 100125 AFDFSD AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 825 PM CDT SAT MAY 9 2009 .DISCUSSION... EXCEPT NEARAR THE MISSOURI RIVER...MOST THUNDERSTORMS HAVE DISSIPATED ACROSS THE REGION. EXPECT THAT THE STORM MOVING INTO KNOX COUNTY NEBRASKA WILL SLOWLY DIMINISH WITH SUNSET BUT DID KEEP A LOW POP FOR THE MISSOURI VALLEY...AS FAR EAST AS DIXON COUNTY...THROUGH 10 PM CDT. OTHERWISE...MOST OF THE CU IS WELL ON ITS WAY TO DYING THIS EVENING...LOW CLOUD OVER ND SHOULD ERODE ON THE SRN END WITH THE LOSS OF DAYTIME HEATING LEAVING MOSTLY CLEAR SKIES ACROSS THE AREA UNTIL SOME CIRRUS...OVER THE WRN PLAINS...MOVES INTO SC SD LATER TONIGHT. WITH WINDS DROPPING OFF FAST AND MOSTLY CLEAR SKIES...MOST AREAS WILL FALL INTO THE 30S WITH MID 30S LIKELY AS FAR SOUTH AS MADISON...FLANDREAU AND SLAYTON. THEREFORE...EXPANDED THE AREA WITH PATCHY FROST INTO THESE AREAS AS WELL. GRIDS OUT...NEW PFM AND ZFP OUT BY 0145 UTC. && .AVIATION... WITH CU AND THUNDERSTORMS DISSIPATING BY 03Z...NO SIGNIFICANT AVIATION CONCERNS EXPECTED OVERNIGHT AS WINDS GO LIGHT AND VARIABLE. WHILE CU EXPECTED TO REDEVELOP BY EARLY TOMORROW AFTERNOON...A LITTLE MORE STABLE...850 TO 700 MB LAPSE RATES AROUND 7 C/KM INSTEAD OF 8.5 C/KM...SO SCATTERED SHRA/TSRA THAT OCCURRED THIS EVENING NOT EXPECTED DURING THE AFTERNOON. HOWEVER...WOULD NOT RULE OUT AN ISOLATED SHRA WEST OF THE JAMES RIVER BUT COVERAGE WOULD BE LESS THAN 20 PERCENT SO WILL NOT MENTION IN TAF. ANY CU BASES SHOULD BE ABOVE 3000 FT. AS WITH TODAY...EXPECT THAT AS MIXING INCREASES AND CU FORMS...WILL SEE WIND INCREASE A LITTLE IN THE AFTERNOON...BUT AGAIN WINDS ALOFT LIGHTER THAN TODAY AND RIDGE BUILDING IN SO WINDS WILL LIKKELY STAY AOB 10 KTS. && .PREV DISCUSSION... SCATTERED MID AFTERNOON SHOWERS DEVELOPING OVER SOUTHEAST SD AND WITH LATE DAY HEATING EXPECT THIS ACTIVITY TO BECOME MORE WIDESPREAD ACROSS THE FORECAST AREA THROUGH EARLY EVENING. AIRMASS COLD ENOUGH FOR ISOLATED LOW TOP THUNDERSTORMS WITH SMALL HAIL LIKELY. SHOWER/TRW ACTIVITY SHOULD QUICKLY DIMINISH AS SUNSET APPROACHES. WELL DEFINED SHORT WAVE IN NORTHWEST FLOW ALOFT OVER SOUTHEAST NORTH DAKOTA THIS AFTERNOON WILL LIKELY GET SHEARED APPARENT AS IT SLIDES SOUTHEAST IN CHANNELED FLOW ALOFT...BUT STILL WILL HAVE AN IMPACT BY KEEPING MOSTLY CLOUDY SKIES ACROSS THE NORTHEAST PORTION OF THE FORECAST AREA PAST MIDNIGHT...ESPECIALLY ACROSS SOUTHWEST MINNESOTA. HOWEVER SKIES SHOULD BECOME CLEAR ACROSS THE NORTH LATE TONIGHT AND WITH LIGHT WINDS...SOME SCATTERED LIGHT FROST POSSIBLE FROM HURON EASTWARD THROUGH BROOKINGS TO THE MARSHALL MN AREA. ELSEWHERE OVERNIGHT TEMPS WILL DROP INTO THE 30S...BUT LESS CHANCE FOR FROST. /GH SUNDAY SHAPING UP TO BE A PRETTY NICE DAY WITH SURFACE HIGH PRESSURE BUILDING INTO THE NORTHERN PLAINS. ALTHOUGH TEMPERATES ALOFT WILL BE SIMILAR TO TODAYS...THINK WE WILL REMAIN DRY THROUGH THE DAY WITH LAPSE RATES AND MOISTURE A LITTLE LESS. ONLY CAVEAT WOULD BE IF THE WEAK BOUNDARY MEANDERING JUST TO OUR SOUTH ON SUNDAY ENDS UP BEING JUST A LITTLE FARTHER NORTH...AND THEN WITH A SHORTWAVE PUSHING OUT OF THE CENTRAL ROCKIES INTERACTING WITH THE FRONT...COULD SEE A FEW SHOWERS ALONG THE MISSOURI RIVER IN THE AFTERNOON. AT THIS POINT...HAVE KEPT ANY POPS OUT OF OUR CWA. HIGH TEMPERATURES LOOK TO BE SIMILAR TO TODAYS...IN THE LOWER TO MID 60S. ON SUNDAY NIGHT AND MONDAY...THE HIGH PRESSURE BEGINS TO MOVE EAST...WITH A RETURNING SOUTHERLY FLOW ON THE BACKSIDE OF THE HIGH. MODELS CONTINUING TO INDICATE A BIT OF ELEVATED INSTABILITY...PER CAPE VALUES IN THE RANGE OF 100 TO 200 J/KG...PUSHING ACROSS OUR NORTHERN ZONES DURING THIS FRAME...BUT STILL LOOKS LIKE MOISTURE WILL BE PRETTY LIMITED AT THAT TIME. WITH A MODERATING AIRMASS...WILL SEE TEMPERATURES CLIMB INTO THE LOWER 70S ON MONDAY AFTERNOON. LATER ON MONDAY NIGHT...MUCH BETTER MOISTURE BEGINS TO SURGE NORTHWARD ON A STRENGTHENING LOW LEVEL JET THROUGH WESTERN SOUTH DAKOTA AS A MID LEVEL WAVE PUSHES OUT OF THE ROCKIES. WILL HAVE STRONG MID LEVEL WAA PUSH ACROSS THE CWA BY TUESDAY MORNING...SO KEPT WITH MODERATE CHANCE POPS WITH BEST FORCING MAINLY IN OUR CENTRAL AND EAST FOR THAT TIME PERIOD. INSTABILITY DOES NOT LOOK THAT GREAT...SO DO NOT THINK THAT SEVERE WEATHER WILL BE AN ISSUE. WILL BE A WINDY DAY ON TUESDAY WITH A 40 KT LOW LEVEL JET LYING ACROSS THE REGION. EVEN WARMER STILL WITH HIGHS INTO THE MID 70S IN OUR WEST. BETTER CHANCE OF POPS COME IN ON TUESDAY NIGHT AND EARLY ON WEDNESDAY WITH STRONG LOW LEVEL CONVERGENCE AS THE MAIN COLD FRONT PUSHES ACROSS OUR AREA...AND CONTINUING ABUNDANT LOW LEVEL MOISTURE ADVECTION WITH THE AFOREMENTIONED LLJ. MODELS ARE NOW A LITTLE FASTER WITH FRONT...SO APPEARS THAT MOST OF THE PRECIPITATION SHOULD BE OUT OF OUR CWA BY EARLY WEDNESDAY AFTERNOON. WITH THE PASSAGE OF THE FRONT...TEMPERATURES WILL BE COOLER...MAINLY IN THE 60S. FARTHER OUT IN THE EXTENDED...THURSDAY IS LOOKING PRETTY DECENT AT THIS POINT AS UPPER LEVEL AND SURFACE RIDGING BUILDS INTO THE REGION. WITH THIS...WILL SEE A BIT OF A WARM UP...THEN MUCH BETTER WARMING WILL BE ACHIEVED ON FRIDAY AS THE UPPER LEVEL RIDGE AXIS PUSHES ACROSS THE REGION AND WE GET BACK INTO A RETURNING SOUTHERLY FLOW WITH THE EXITING SURFACE HIGH. MAY GET AROUND 80 IN OUR WESTERN ZONES WITH 850 MB TEMPS CLOSING IN ON 20 DEGREES C. BY FRIDAY NIGHT AND SATURDAY...COULD KICK OFF SOME THUNDERSTORM ACTIVITY WITH STRONG MOISTURE TRANSPORT INTO THE REGION ON A STRENGTHENING LLJ...IN ADVANCE OF A WAVE PUSHING OUT OF THE ROCKIES. MODEL DIFFERENCES BECOME RATHER SIGNIFICANT BY THE END OF THE EXTENDED... WITH GFS/ECMWF DIFFERING ABOUT 6 HOURS IN REGARD TO TIMING OF COLD FRONT SOME TIME IN THE LATE FRIDAY NIGHT TO SATURDAY TIME FRAME. THIS WILL ULTIMATELY MAKE A BIG DIFFERENCE IN TEMPERATURES ON SATURDAY...BUT WENT WITH THE SLOWER/WARMER SOLUTION AT THIS POINT. /JM && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && $$ SCHUMACHER
