000 FXUS63 KLSX 141147 AFDLSX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE ST LOUIS MO 645 AM CDT SAT JUL 14 2007 .DISCUSSION... CHALLENGING FORECAST FOR THE NEXT FEW DAYS AS YET ANOTHER WEAK FRONT DRIFTS INTO THE CWFA FROM THE NORTH. RAIN POTENTIAL IS NOT EASY TO DISCERN AS THE FRONT WILL HAVE ONLY VERY WEEK CONVERGENCE ALONG IT AND UPPER LEVEL DYNAMICS ARE TOO FAR NORTH ASSOCIATED WITH THE SHORTWAVE. BOTH GFS AND NAM ARE FORECASTING MODERATE AMOUNTS OF INSTABILITY...MLCAPE ABOVE 2000 J/KG...WITH THE NAM HAVING THE HIGHEST MLCAPE VALUES WELL ABOVE 3000 J/KG. AM LEANING TOWARD THE LESS ENTHUSIASTIC GFS SOLUTION WITH THIS FRONT AS THE NAM HAS NOT HANDLED THE THERMODYNAMIC FIELDS ALL THAT WELL FOR THE PAST COUPLE OF SYSTEMS TO AFFECT THE AREA. SPC NMM 4KM WRF MODEL BREAKS OUT A LINE OF CONVECTION AROUND 00Z UP IN EXTREME SOUTHERN IOWA ALONG THE FRONT AND THEN ROLLS IT SOUTHWARD INTO OUR AREA. THE LINE BREAKS APART THE FURTHER SOUTH IT GOES OVERNIGHT...WITH SCATTERED CONVECTION CONTINUING INTO CENTRAL MISSOURI AFTER MIDNIGHT WHERE THE INSTABILITY IS HIGHEST...AND ANOTHER LINE SEGMENT CONTINUING EAST INTO CENTRAL AND EASTERN ILLINOIS WHERE THE DYNAMICS IS STRONGER. THIS WOULD LEAVE THE CENTRAL PORTION OF THE CWFA...THE ST. LOUIS METRO AREA AND POINTS SOUTH...PRETTY MUCH HIGH AND DRY. IF THE MUCH MORE ENERGETIC NAM TURNS OUT TO BE MORE CORRECT THAN THE GFS WE COULD SEE SOME SEVERE STORMS FORM...PRIMARILY OVER NORTHWEST PORTIONS OF THE CWFA AS THE SWODY1 SUGGESTS. HOWEVER...DEEP SHEAR IS LESS THAN IMPRESSIVE...SO EVERY BIT OF THE HIGHER CAPE WILL BE NEEDED TO FORCE STRONG UPDRAFTS. IF THE LOWER-CAPE GFS IS MORE CORRECT...SEVERE STORMS WILL BE DIFFICULT TO COME BY. DEPENDING ON WHAT HAPPENS WITH OVERNIGHT CONVECTION THE EFFECTIVE FRONT COULD END UP JUST ABOUT ANYWHERE ACROSS MISSOURI ON SUNDAY. NAM IS AGAIN MUCH MORE ENERGETIC THAN THE GFS...AND HAS LITTLE OR NO CAP SUNDAY AFTERNOON TO HOLD DOWN UPDRAFTS. ONLY HAVE SLIGHT CHANCES GOING IN SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS FOR SUNDAY FOR THIS PACKAGE...BUT WILL KEEP IN MIND THE POSSIBILITY OF INCREASING POPS ON SUNDAY ON LATER UPDATES. OF COURSE...WIDESPREAD CONVECTION COULD MESS UP THE TEMPERATURE FORECAST FOR SUNDAY AFTERNOON...SO CONFIDENCE IS NOT REALLY HIGH FOR SUNDAY. WEAK NORTHWEST FLOW AT 500MB CONTINUES TO HANG OVER THE AREA INTO THE BEGINNING OF THE WEEK AS THE STRONG LONGWAVE TROF PERSISTS OVER THE EASTERN 1/3 OF THE COUNTRY AND A STRONG UPPER RIDGE BUILDS IN TO THE NATIONSS MIDSECTION. LOWER LEVEL WEST-SOUTHWESTERLY FLOW DEVELOPS OVER THE MIDWEST AND THE PLAINS WHICH USHERS SUMMER HEAT AND HUMIDITY BACK INTO THE AREA. NORTHERN PORTIONS OF THE AREA COULD SEE SOME RAIN AS THE TAIL ENDS OF SEVERAL MCSS WHICH COULD FORM OVER PORTIONS OF THE UPPER MIDWEST MOVE ACROSS ILLINOIS...BUT IT LOOKS LIKE MOST OF THE AREA WILL STAY HOT...HUMID...AND PRECIP FREE EXCEPT FOR THE OCCASIONAL AFTERNOON THUNDERSTORM THROUGH THE END OF THE WEEK. CARNEY && .AVIATION... FOR THE 12Z TAFS...VFR CONDITIONS WILL PREVAIL ACROSS THE FORECAST AREA THRU THE VALID TAF PERIOD. MAIN PCPN CHANCES WILL REVOLVE AROUND CDFNT PUSHING S INTO NERN MO/CNTRL IL EARLY THIS EVENING...REACHING SOUTHERN MO AND IL BY SUNDAY MORNING. HAVE PROB30S FOR TSRA/SHRA FOR THE KUIN/KCOU TAFS...BUT LEFT MENTION OF PCPN OUT OF KSTL AREA. SWLY FLOW EXPECTED AHEAD OF CDFNT TODAY WILL VEER NWLY BEHIND CDFNT TONIGHT. SDT && .LSX WATCHES/WARNINGS/ADVISORIES... MO...NONE. IL...NONE. && $$ WFO LSX