000 FXUS63 KFSD 131547 AFDFSD AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 1045 AM CDT THU SEP 13 2007 .DISCUSSION... HAVE TWEAKED THE GRIDS AND UPLOADED...AND WL UPDATE THE ZFP SOON. GOING FCST IS GOING WELL HOWEVER. BASED ON CURRENT READINGS... ADJUSTED A FEW HIGHS ONLY A COUPLE OF DEGS AS OVERALL MIXING THRU THE FSD FA IS SLIGHTLY ABOVE H85 TODAY BEHIND THE STRONG CDFNT PASSAGE. SPEAKING OF WHICH...AT 15Z THE LEADING EDGE OF THE FRONT WAS WELL INTO NW IA...JUST ABOUT ON TOP OF A KSUX TO KSPW LINE. STRATOCU DEEPER BEHIND THE FRONT HAS BEEN DRYING UP RECENTLY DUE TO SUBSIDENCE AND MIXING. BUT A NEW LINE OF CAA STRATOCU HAS FORMED JUST BEHIND THE FRONT. BELIEVE IN TIME...THE SAME THING MAY HAPPEN TO THAT AREA OF CLOUDS ALSO. WIND WISE...ADJUSTED SOME SPEEDS DOWNWARD IN OUR NW QUARTER. TOOK A GOOD LOOK AT THE 12Z NAM WIND TRENDS. IT LOOKS AS THOUGH THE STRONGEST LOW LEVEL CAA AND SFC PRS RISES ARE WEAKENING DRAMATICALLY BEHIND THE FRONT BY 18Z. SO WE ARE MAINLY LEFT WITH JUST MIXING WINDS. THE WINDS OFF THE SFC IN THE DRY ADIABATIC LAYER ARE NOT ALL THAT BRUTALLY STRONG...BUT IT WL STILL BE BREEZY TO WINDY AT ALL LOCATIONS. FINALLY...NOTCHED BACK OUR 20 POPS IN OUR SERN CWFA TO JUST SCT SPRINKLES ALONG THE LOW LEVEL FRONTOGENESIS ZONE. ATTM...DO NOT BELIEVE ANYTHING WL MEASURE AND CURRENT INSTABILITY ALOFT FIELDS INDICATE THAT THERE IS NOT A THREAT FOR TS. && .AVIATION... SHOULD BE PRIMARILY VFR CONDS. THERE COULD BE SOME SHREDS OF MVFR CIGS IN THE KSUX AREA EARLY THIS AFTN BEFORE THEIR LINE OF POST FRONTAL CU BEGINS TO DRY OUT. BUT OVERALL...WERE LOOKING AT VFR THE NEXT 24 HRS. && .PREV DISCUSSION... A COUPLE OF ACCAS SHRA/TSRA HAVE POPPED UP IN AXIS OF ELEVATED INSTABILITY SOUTHEAST OF YKN-FSD LINE EARLY THIS MORNING. MAIN AXIS OF INSTABILITY QUICKLY SHIFTS SOUTHEAST OF THE CWA BETWEEN 12Z-15Z BUT WILL CARRY MENTION OF ISOLATED SHRA/TSRA ACROSS NORTHWEST IOWA IN THE ZFP FOR THE EARLY MORNING. AS OF 09Z...STRONG COLD FRONT IS NEAR A KBKX-KONL LINE...AND MODELS IN PRETTY GOOD AGREEMENT ON TIMING BOUNDARY TO NEAR KMJQ-KSUX LINE BY MIDDAY. FRONT SHOULD BE MOVING FAST ENOUGH TO PRECLUDE ANY ADDITIONAL DEVELOPMENT DURING THE AFTERNOON IN OUR CWA...BUT WITH SOME LINGERING ELEVATED INSTABILITY IN EXTREME SOUTHEAST CORNER...THOUGHT IT WORTH A SLIGHT CHANCE FOR KSPW/KSLB AREAS DURING THE EARLY AFTN. AS FAR AS SCATTERED BAND OF SPRINKLES SEEN ON REGIONAL RADAR MOSAIC ACROSS FAR NRN SD/SRN ND THIS MORNING...EXPECT THIS TO SHEAR EAST WITH THE UPPER WAVE AND REMAIN NORTH OF OUR CWA. TEMPS REMAINED PRETTY MILD OVERNIGHT WITH STOUT SOUTH WIND...SO UPPED MORNING TEMPS EVEN BEHIND THE COLD FRONT WHERE STRONG MIXING IS EXPECTED. STRONGEST PUSH OF 850MB COLD ADVECTION THROUGH MOST AREAS BY 18Z...SO STILL LOOKING FOR MOST AREAS TO REACH THEIR DAYTIME HIGH AROUND MIDDAY. MUCH WEAKER COLD ADVECTION WITH MODEL 850MB TEMPS HOLDING PRETTY STEADY THROUGH THE AFTERNOON...AND WOULD EXPECT WELL MIXED SURFACE TEMPS TO DO THE SAME. SURFACE RIDGE AXIS REMAINS WEST OF OUR CWA TONIGHT...SO WHILE SOME WESTERN PARTS OF THE CWA COULD SEE TEMPS DROP INTO THE 36-38F RANGE IN COLD AIRMASS BY DAYBREAK...EXPECT WINDS TO STAY UP ENOUGH TO PREVENT FROST DEVELOPMENT IN OUR CWA TONIGHT. COLDEST PORTION OF THE AIRMASS MOVING ACROSS THE CWA DURING DAYTIME HOURS FRIDAY...WITH GFS/NAM/ECMWF/UKMET ALL IN GOOD AGREEMENT SHOWING SUBZERO 850MB TEMPS ACROSS THE NORTHEAST HALF OF THE CWA AT 18Z...WARMING TO A SHADE ABOVE ZERO BY 00Z. THIS WILL BE COLDEST DAY BY FAR...WITH MOST AREAS LIKELY NOT TOPPING 60F...EVEN WITH PLENTIFUL SUNSHINE AND DECENT MIXING. CORE OF COOL SURFACE HIGH REALLY MOVES THROUGH THE CWA DURING THE EVENING HOURS...ALLOWING MOST AREAS TO SEE SLIGHT RECOVERY IN WINDS BY LATE NIGHT. SHOULD SEE VERY QUICK DROP FROM ALREADY COOL TEMPS DURING THE EVENING...WITH GENTLE FALL THE REMAINDER OF THE NIGHT. STILL LOOKS COOL AND DRY ENOUGH FOR FROST DEVELOPMENT...AND COULD BE FAIRLY WIDESPREAD AROUND RADIATIONALLY FAVORED AREA AROUND THE IOWA GREAT LAKES. TOO EARLY TO PIN DOWN ADVISORY POTENTIAL...BUT WILL CONTINUE TO HIGHLIGHT IN HWO. HIGH QUICKLY SHIFTS EAST WITH INCREASING SOUTHERLY FLOW AND WARM ADVECTION ON SATURDAY. GFS AND NAM BOTH SHOWING STRONG ISENTROPIC LIFT AND RESPECTABLE RH LEVELS MOVING ACROSS THE SOUTHEAST PORTIONS OF THE CWA SATURDAY AFTERNOON...WITH SOME ELEVATED INSTABILITY INDICATED AS WELL. HAVE ADDED SMALL CHANCE OF SHRA/ISOLATED TSRA TO FROM AROUND KYKN INTO NORTHWEST IOWA FOR THE AFTERNOON...LINGERING IN FAR EAST EARLY SATURDAY EVENING. WARMUP CONTINUES THROUGH THE EARLY PART OF THE NEXT WEEK...AND MODELS TRENDING WARMER WITH LOW LEVEL TEMPS BENEATH WEAK UPPER LEVEL RIDGING...SO HAVE BEGUN TO NUDGE SUNDAY NIGHT LOWS AND MONDAY HIGHS WARMER...THOUGH DAY SHIFT WILL WANT TO EXAMINE MORE CLOSELY AND POSSIBLY INCREASE MORE. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && $$ MJF