000 FXUS63 KPAH 110139 AFDPAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PADUCAH KY 839 PM CDT SAT MAY 10 2008 .UPDATE... SURFACE COLD FRONT WAS OVER EXTREME WESTERN MISSOURI AT 01Z...JUST EAST OF A KANSAS CITY TO JOPLIN LINE. 21Z RUC RACES THE FRONT EASTWARD ACROSS THE LOWER OHIO VALLEY BY 09Z. SURFACE BASED INSTABILITY IS STILL LACKING OVER OUR REGION...WITH SBCAPES BARELY REACHING 200 J/KG ALONG THE TENNESSEE BORDER. IT APPEARS UNLIKELY THAT SURFACE BASED INSTABILITY WILL INCREASE OVERNIGHT...AS CONVECTIVE OUTFLOW WILL IMPEDE THE NORTHWARD PROGRESS OF A WARM FRONT VICINITY OF I 40. THEREFORE...MAIN SEVERE WEATHER HAZARD SHOULD BE ELEVATED HAILERS. VERY STRONG MID LEVEL WIND FIELDS ASSOCIATED WITH POWERFUL 500 MB SHORTWAVE WILL FAVOR SOME ELEVATED SUPERCELLS AND RISK OF ISOLATED DAMAGING WINDS. POTENTIAL FOR A STRONG WIND EVENT APPEARS TO EXIST LATE TONIGHT AND SUNDAY. ISALLOBARIC CONTRIBUTION WILL BE SIGNIFICANT DUE TO THE EXTREMELY FAST MOVEMENT OF THE FRONT. 21Z RUC SHOWED 850 MB WINDS AROUND 60 KNOTS BY 09Z. WHILE MIXING HEIGHTS WILL NOT BE THAT HIGH...THESE LOW LEVEL WIND FIELDS SUGGEST THAT WIND ADVISORY CRITERIA MAY BE MET. WIND GUSTS FROM 35 TO 45 MPH ARE BEING REPORTED BEHIND THE FRONT OVER ERN KANSAS/FAR WEST MISSOURI. A WIND ADVISORY MAY BE REQUIRED FOR THE FORECAST AREA LATER TONIGHT OR SUNDAY. && .PREVIOUS DISCUSSION /ISSUED 255 PM CDT SAT MAY 10 2008/... SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... MAIN FORECAST CONCERNS WITH THIS PACKAGE CONTINUE TO LIE WITH THE SEVERE WEATHER POTENTIAL TONIGHT. THE ECMWF/NAM/GFS CONTINUE IN VERY GOOD AGREEMENT WITH THE SPEED/PLACEMENT/INTENSIFICATION OF THE DEEPENING MID LEVEL SHORT WAVE THAT RAPIDLY BECOMES A CLOSED LOW OVER IL BY LATER TONIGHT. IN RESPONSE...THE SURFACE LOW WILL ALSO BE DEVELOPING VERY QUICKLY TONIGHT AS IT MOVES THROUGH SRN IL. THE SURFACE FRONT SHOULD BEGIN SWEEPING QUICKLY EAST LATE THIS AFTERNOON AS MID LEVEL JET PUNCHES IN FROM THE WEST. LOOK FOR AN INCREASING CHANCE OF SHOWERS AND THUNDERSTORMS LATE THIS AFTERNOON ACROSS OUR WESTERN MOST COUNTIES...SHIFTING RAPIDLY EAST ACROSS THE FA IN THE DURING THE FIRST 1/2 OF TONIGHT. MODELS CONTINUE TO PROG STRENGTHENING WIND FIELDS ALOFT AS THE EVENING WEARS ON...INCREASING 0-1 KM HELICITY VALUES INTO THE 400 TO 600 RANGE AHEAD OF THE FRONT. ONE POSSIBLE INHIBITOR TO WIDESPREAD SEVERE OUTBREAK MAY LIE WITH MARGINAL INSTABILITIES. HOWEVER...WILL NOT NEED A TREMENDOUS AMOUNT OF INSTABILITY TO PRODUCE SEVERE STORMS IN SUCH AN ENVIRONMENT. ANY CELLS THAT DO FORM WILL LIKELY HAVE A TENDENCY TO ROTATE...SO A FEW TORNADOES ARE A DISTINCT POSSIBILITY...ESP IN THE MORE UNSTABLE AIR OF SE MO/WRN KY AND THE SRN TIP OF IL. DRY SLOT SEEN IN THE MODELS REACHES AS FAR EAST AS PAH BY 06Z...AND SPREADS EAST ACROSS THE REST OF THE FA 06-09Z. WILL RAPIDLY DECREASE POPS FROM WEST TO EAST IN THE 06-12Z TIME FRAME. SUNDAY...THE CLOSED LOW WILL MOVE EAST ACROSS THE OHIO VALLEY. AS THE SURFACE LOW DEPARTS WITH IT...A DECENT PRESSURE GRADIENT WILL FOLLOW ON THE BACKSIDE OF THE SYSTEM...SO GUSTY W/NW WINDS ARE A CERTAINTY IN THE WAKE OF THE SYSTEM SUNDAY. MANY AREAS WILL LIKELY SEE WIND GUSTS FROM 30 TO 45 MPH. WRAP AROUND SHOWERS WILL BE LIKELY AS WELL N AND NE AREAS...WITH BEST CHANCE EVV TRI-STATE. WILL END THE SHOWER CHANCE BY MID EVENING SUNDAY NIGHT ACROSS OUR EASTERN COUNTIES AS THE LOW DEPARTS. MONDAY AND MONDAY NIGHT SHOULD BE DRY AND GENERALLY CLOUD FREE AS HIGH PRESSURE MAKES A BRIEF APPEARANCE. WILL SEE SOME CHILLY 40S AT NIGHT...BUT HIGHS SHOULD BE BACK UP AROUND 70 OR SO BY MON AFTERNOON. LONG TERM /TUESDAY THROUGH SATURDAY/... PRECIPITATION POTENTIAL WILL NOT ABATE FOR LONG AS THE UPPER LEVEL RIDGE RESPONSIBLE FOR THE DRY START TO THE WORK WEEK SHIFTS EAST OF THE REGION BY TUESDAY. THIS WILL ALLOW FOR A RETURN OF MOISTURE ON INCREASING SOUTHERLY FLOW...AND EVENTUALLY CHANCES FOR SHOWERS AND THUNDERSTORMS AS AN UPPER-LEVEL WAVE PIVOTS AROUND LOW PRESSURE OVER ONTARIO CANADA. THE PASSAGE OF THIS WAVE AND ITS ASSOCIATED COLD FRONT WILL LEAD TO AN INCREASING CHANCE FOR SHOWERS AND STORMS BEGINNING TUESDAY AND LASTING INTO WEDNESDAY. BEYOND WEDNESDAY...THE FORECAST BECOMES LESS CLEAR. SUCCESSIVE RUNS OF THE ECMWF AND GFS HAVE WAVERED SIGNIFICANTLY ON THE EVOLUTION OF THE LARGE-SCALE SYNOPTIC PATTERN OVER THE CENTRAL AND EASTERN PART OF THE NATION. ONE POSSIBLE SCENARIO IS THE DEVELOPMENT OF A CLOSED UPPER LOW OVER THE GREAT LAKES REGION WHICH WOULD PLACE THE IMMEDIATE AREA IN CYCLONIC FLOW. ANOTHER MORE LIKELY SCENARIO IS THE DEVELOPMENT OF A LONGWAVE TROUGH OVER THE CENTRAL AND EASTERN PART OF THE NATION AS THE NORTHERN AND SOUTHERN STREAMS ATTEMPT TO PHASE. GIVEN THE MODEL UNCERTAINTY AT THIS TIME...WE WILL MAINTAIN A CHANCE OF SHOWERS THROUGH FRIDAY...WITH A RETURN TO DRY CONDITIONS HEADING INTO NEXT WEEKEND. USED A BLEND OF HPC AND GFS GUIDANCE FOR THE EXTENDED. THIS RESULTED IN FEW CHANGES TO EXISTING FORECAST. && .AVIATION... LOW PRESSURE WILL RAPIDLY INTENSIFY AS IT TRACKS ACROSS MISSOURI AND ILLINOIS TONIGHT. AS THE LOW DEEPENS AND MOVES EAST...WINDS WILL STRENGTHEN FROM THE SOUTHEAST THIS EVENING...THEN SHIFT TO THE WEST WITH THE PASSAGE OF A COLD FRONT OVERNIGHT. WINDS BEHIND THE FRONT WILL BECOME VERY STRONG...ESPECIALLY ON SUNDAY. SUSTAINED WINDS WILL AVERAGE 15 TO 25 KNOTS...WITH GUSTS TO AT LEAST 35 KNOTS AT TIMES. SHOWERS AND THUNDERSTORMS WILL ACCOMPANY THE PASSAGE OF THE COLD FRONT TONIGHT...MOST LIKELY THIS EVENING AT KCGI AND KPAH...THEN WITHIN A FEW HOURS OF MIDNIGHT AT KEVV AND KOWB. VFR CONDITIONS WILL PREVAIL PRIOR TO FRONTAL PASSAGE...WITH THE EXCEPTION OF REDUCED CEILINGS AND VISIBILITIES ASSOCIATED WITH THUNDERSTORM ACTIVITY. MVFR CEILINGS ARE EXPECTED BEHIND THE FRONT LATE TONIGHT INTO SUNDAY. && .PAH WATCHES/WARNINGS/ADVISORIES... KY...NONE. MO...NONE. IL...NONE. IN...NONE. && $$ .UPDATE...MY .PREVIOUS...MEFFERT/RJP .AVIATION...RJP