000 FXUS63 KFSD 240318 AFDFSD AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 918 PM CDT THU APR 23 2009 .DISCUSSION... COLD FRONT MOVING ACROSS THE AREA FASTER THAN ANY MODELS EARLIER INDICATED. MADE UPDATES TO GRIDS ACCORDING...SPEEDING UP THE WIND DIRECTION CHANGE AND DROPPING TEMPERATURES FURTHER AND FASTER. LATEST 00Z NAM AND RUC STILL TO SLOW...BUT DO EXPECT FRONT TO SLOW SOME AS IT MOVES ACROSS THE AREA TONIGHT. DIFFICULT TO SAY EXACTLY HOW FAR THE FRONT WILL MAKE IT TONIGHT...BUT LOWERED LOWS IN ALL BUT NW IA. BASED ON UPSTREAM TEMPERATURES...SHOULD DROP INTO THE LOWER TO MID 40S OVER MUCH OF THE NORTHERN AND WESTERN CWA TONIGHT. AT ANY RATE...NO REPEAT OF THE WIDESPREAD RECORD TEMPERATURES WHICH WERE EXPERIENCED ACROSS THE AREA TODAY. SOME ELEVATED INSTABILITY HAS BEEN TRYING TO PRODUCE ISOLATED CONVECTIVE ACTIVITY JUST N OF SUX EARLIER THIS EVENING. DO NOT EXPECT THEN ANY MOISTURE MADE IN TO THE GROUND PROVIDED THE VERY DRY LOW/MID LEVELS. CONVECTIVE ACTIVITY IN WRN SD WANING AS IT MOVES EAST. MODELS DO INDICATE STEEP ELEVATED LAPSE RATES AND SOME UPPER LEVEL MOISTURE...SO WOULD NOT BE SURPRISED TO SEE SOME RADAR ECHOS SLIDE THE CWA TONIGHT...BUT REALLY NOT EXPECTING MUCH IF ANY RAIN TO REACH THE GROUND. ADDED A CHANCE OF SPRINKLES FOR THIS POSSIBLE CONVECTIVE ACTIVITY. && .AVIATION... SFC CDFNT HAS PUSHED SEWD THROUGH KHON AS OF 02Z...AND TIMING OF CDFNT THROUGH THE REMAINDER OF THE FA IS CHALLENGE FOR THE REST OF TONIGHT. TIMING THROUGH ERN SD THUS FAR HAS BEEN QUITE A BIT FASTER THAN ANY MODELS HAD INDICATED. 01Z RUC TRYING TO CATCH UP TO REALITY BUT STILL A COUPLE OF HOURS SLOW. SEEING A COUPLE OF FINE LINES ON KFSD AND KLNX 88D LOOPS THAT ARE MOVING TO THE WEST/NORTHWEST. THIS COULD BE INDICATIVE OF SOUTHERLY LOW LEVEL JET BEGINNING TO INCREASE ACROSS THE REGION...WHICH CAN ALSO BE SEEN IN REGIONAL PROFILER AND RADAR VWP DISPLAYS INCREASING TO 40-50 KNOTS IN LOWEST GATES AS OF 02Z. THINK LOW LEVEL JET WILL HELP SLOW THE SEWD PROGRESSION OF THE FRONT SOME THIS EVENING...THO WILL GO WITH TIMING IN THE TAFS THAT IS STILL A TOUCH FASTER THAN MOST MODEL GUIDANCE...BRINGING A SWITCH TO NORTHERLY WINDS INTO KFSD BY 10Z. KSUX TRICKIER AS MUCH OF THE GUIDANCE POINTS TO FRONT STALLING NEAR OR JUST SHY OF KSUX. HOWEVER 00Z NAM SHOWS THE FRONT PUSHING THROUGH KSUX 15Z-18Z WINDOW PRIOR TO STALLING NEAR SOUTHEAST EDGE OF OUR FA. WITH FASTER TIMING SEEN ALREADY...THIS MAY BE BETTER CHOICE AND WILL TAKE A CLOSER LOOK AT THIS FOR THE UPCOMING 06Z TAF ISSUANCE. LOCATIONS AHEAD OF THE CDFNT COULD SEE PERIOD OF LLWS OVERNIGHT AS BOUNDARY LAYER DECOUPLES FURTHERN AND LOW LEVEL JET INCREASES TO 50+ KTS JUST ABOVE THE INVERSION. LOCATIONS FARTHER BEHIND THE BOUNDARY WILL SEE SOME STRONGER NORTHERLY GUSTS AS DEEPER PORTION OF THE BOUNDARY ALLOWS FOR MIXING 25-30KT GUSTS DOWN TO THE SURFACE. THIS MOST LIKELY TO AFFECT KHON...AS DO NOT EXPECT FRONT TO MOVE FAR ENOUGH SOUTHEAST FOR THIS DEEPER MIXING TO GET INTO KFSD/KSUX. && .PREV DISCUSSION... WARM AND BREEZY CONDITIONS WILL CONTINUE THROUGH THE OVERNIGHT HOURS AS A COLD FRONT APPROACHES FROM THE NORTH. AT THIS POINT...IT APPEARS THAT IT IS FAR TOO DRY ALONG AND AHEAD OF THIS FRONT...SO WILL ONLY INCLUDE LOW POPS...LESS THAN 20...IN THE FAR NORTH AS SOME WEAK UPPER LEVEL SUPPORT MOVES THROUGH. OTHERWISE...VERY MILD AHEAD OF THE FRONT WITH LOWS IN THE LOWER 60S IN MUCH OF NORTHWEST IOWA...FALLING TO LOWS IN THE MID 40S NORTH TOWARDS HURON WHERE THE COLDER AIR WILL BEGIN TO LEAK IN SHORTLY AFTER ABOUT 11-12Z. CLEAR SKIES AHEAD OF THE FRONT WILL LEAD TOWARDS MOSTLY CLOUDY MID TO HIGH CLOUDS BEHIND THE FRONT. WILL LET THE RED FLAG WARNING AND WIND ADVISORY DIE AT 00Z AND 01Z AS THE SUN SETS...WINDS DECREASE...DEW POINTS POP UP A FEW DEGREES AND THE TEMPERATURES BEGINS TO FALL. /08 STRONG FRONTAL BNDRY THE FOCUS FOR THE SHORT TERM. ELEVATED INSTABILITY AND A LITTLE WEAK DISTURBANCE EARLY IN THE DAY COULD YIELD ISOLD HIGH BASED SHRA/TSRA ACRS FAR NRN/NERN CWA BEFORE THREAT PULLS OUT BY MID MORNING. WITH THE VERY WARM AND MIXED LYR ALFT... WL HAVE TO WAIT UNTIL MID LVL BNDRY 750-650 HPA STARTS TO DROP SWRD TO INCREASE PCPN THREAT TOWARD EVENING. NOT AS CONCERNED WITH FIRE WX THREAT ON FRIDAY AS SHUD GET ANOTHER BOOST IN LOW LVL MOISTURE OVER TODAY WITH 50S EXPECTED...WHILE PREFRONTAL MIXING ALLOWS INTO THE LOWER TO MID 80S. FRONT IS EXPECTED TO CLEAR FAR SERN CWA BY VERY LATE AFTN. STILL FEEL THAT FOR MOST PART THE MODELS ARE OVERFORECASTING LOW LVL DWPTS NEAR BNDRY ON FRIDAY AFTN AND MAKING THINGS MORE UNSTABLE AND EASIER FOR IMPRESSIVE CAP TO BREAK. THEREFORE...WL ONLY KEEP MINIMAL CONVECTIVE THREATS VERY LATE AFTN...AS STILL LACK MORE THAN SHALLOW LOW LVL FRONTAL FORCING TO INCITE CONVECTION...AND LKLY NOT STRONG ENOUGH ALONE TO OVERCOME CAP...AND ANY SVR THREAT IS EXTREMELY CONDITIONAL LTR FRI AFTN/EVNG. IF DO GET DEVELOPMENT...WOULD LKLY BE RAPID AND WITH CAPES NRG 2000 J/KG AND SHEAR CONCENTRATED IN LOWER 3KM AS LLJ INCREASES...EXPECT WIND TO BE PRIMARY THREAT WITH STORMS WITH SOME POTENTIAL FOR LARGE HAIL. MUCH MORE LIKELY THAT TS BEGIN TO DEVELOP JUST ELEVATED OF BNDRY DURING THE EVNG HOURS AS LLJ INCREASES IN RESPONSE TO APPROACHING PV IMPULSE WHICH MOVES THROUGH LATE NIGHT AND EARLY SATURDAY. BEST PCPN COVERAGE SHUD OCCUR THRU MAIN MID LVL BNDRY...AND AGAIN IN FAR SERN CWA. WHILE TMPS SUGGEST THAT IT MAY GET A BIT DICEY TO KEEP ALL LIQUID IN FCST ACRS FAR NRN/NWRN AREAS...WL KEEP ALL RAIN FOR NOW WITH MID LVL TMPS REMAINING NEAR ZERO...DESPITE A SHADE COOLER BLO. ON SATURDAY...THE WAVE WL CONTINUE TO PRODUCE AREAS OF PRECIP IN THE MORNING...BUT SHUD BE DIMINSHING AS ISENTROPIC UPGLIDE TO THE SOUTH WKNS AND LOSS OF UPR SUPPORT ALG MID LVL BNDRY. POTENTIAL TO GET LITTLE INCREASE AGAIN LATE IN FAR S...BUT HOLDING AT MIDDLE CHC POPS FOR THE TIME IN THE LATE AFTN. A MUCH COOLER DAY EXPECTED...AND TMPS DID NOT APPEAR TO NEED A GREAT DEAL OF ALTERATION FROM BLO NORMAL NUMBERS. HEADING THRU SAT NIGHT...ANOTHER STRONG IMPULSE WL EJECT INTO THE PLAINS AND LIFT NORTH SUNDAY. IN RESPONSE...INCREASE IN LLJ AND LOW LVL BNDRY SUGGESTED TO LIFT NWRD...AND WHILE IN REALITY MAY NOT DO QUITE AS MUCH AS FCST...WL GET DECENT ISENTROPIC LIFT AND ELEVATED INSTABILITY BACK INTO AREA. THIS SHUD BE PERIOD OF HEAVIEST PCPN AS WL NOT GET A STRONG CLEARING OF BNDRY FAR FROM AREA WITH FRIDAY NIGHT/SAT PUSH. PRECIPITATION COULD BE HEAVY SAT NIGHT INTO EARLY SUNDAY...BUT LOOKS TO BE FOCUSED MAINLY SERN HALF OF AREA WHICH IS IN MORE NEED OF PCPN. ANOTHER WELL BLO NORMAL DAY ON SUNDAY...WITH HIGHS MAINLY UPPER 40S AND 50S...CREEPING TOWARD 60 IN THE FAR SE. FOR THE EXTENDED RANGE /SUN NIGHT THRU THU/ SOME MORE BROAD AGREEMENT ON THE LARGER SCALE WITH MUCH LESS ENSEMBLE HEARTBURN...BUT DETAILS IN THE VARIOUS OPERATIONAL RUNS MUCH MORE DIFFICULT TO DIGEST. THE GENERAL PHILOSOPHY OF WRN TROUGH AND CNTRL/ERN U.S. RIDGE YIELDING WEST TO SW FLOW. TMPS SHUD HOVER FAIRLY CLOSE TO NORMALS OVERALL... WITH BETTER MIXING IN THE NE LOW LVL FLOW ON MONDAY INTO TUE. STARTED TO INTRODUCE THUNDER BY LATER WEDNESDAY AS STRONGER LLJ RETURN...AND BEST CHC PCPN BY THU MOST AREAS AS ANOTHER WAVE PUSHES THRU UPSTREAM SIDE OF BROAD RIDGE. /CHAPMAN && .FSD WATCHES/WARNINGS/ADVISORIES... IA...NONE MN...NONE. NE...NONE. SD...NONE. && $$ UPDATE...97/JH