365 FXUS63 KLSX 091750 AFDLSX AREA FORECAST DISCUSSION...UPDATED AVIATION NATIONAL WEATHER SERVICE ST LOUIS MO 1250 PM CDT TUE JUL 9 2013 .SHORT TERM...(THROUGH LATE THIS AFTERNOON) ISSUED AT 304 AM CDT TUE JUL 9 2013 FORECAST FOCUS FOR TODAY CONTINUE TO CENTER AROUND PRECIP TRENDS...WITH A SUBTLE INCREASE IN DEWPOINTS ALSO CAUSING CONCERN FOR HIGH AFTERNOON HEAT INDEX READINGS. IN REGARDS TO PRECIP...BROAD BUT NOT PARTICULARLY STRONG WAA IN PLACE ACROSS THE REGION EARLY TODAY. LATEST HI-RES DATA SUGGESTS NO REAL CHANGE IN THIS LIFTING MECHANISM THROUGHOUT MUCH OF THE MORNING...AND THINK THIS WILL ALLOW SOME THREAT OF ELEVATED CONVECTION OVER ABOUT THE NE HALF OF THE CWA AT ANY TIME. HOWEVER...IT WOULD APPEAR THAT THE GREATEST THREAT WILL BE OVER OUR N COUNTIES...AND THINKING THAT PERSISTENT WAA SHOULD ALLOW SOME INCREASE IN COVERAGE ON S EDGE OF CONVECTION CURRENTLY APPROACHING FAR NW MO. DURING THE AFTERNOON WEAK WAA IS FORECAST TO PERSIST ACROSS THE REGION...WITH SOME SUBTLE SIGNS IN THE MODEL DATA OF A WEAK VORT MAX PROPAGATING INTO THE AREA. OBVIOUSLY...THERE IS PLENTY OF INSTABILITY TO SUPPORT CONVECTION BUT FORECAST SOUNDINGS IN A FEW SPOTS ARE ALSO INDICATING ENOUGH OF A CAP THAT SURFACE BASED CONVECTION WOULD BE INHIBITED. DONT BELIEVE THE THREAT OVER MOST OF THE AREA IS ALL THAT HIGH...BUT BECAUSE THERE ARE SOME PARAMETERS THAT WOULD SUPPORT CONVECTION WILL CONTINUE WITH GOING TRENDS FOR THE AFTERNOON HOURS...GENERALLY LOW POPS OVER ALL BUT OUR FAR SW COUNTIES. ITS CERTAINLY GOING TO BE A VERY HUMID DAY...ESPECIALLY BY THIS SUMMER'S STANDARD. USED SEVERAL METHODS FOR CALCULATING DEWPOINTS TODAY...AND EACH YIELD SIMILAR READINGS OF 70-75 DURING THE AFTERNOON. THIS COUPLED WITH TEMPERATURES IN THE LM90S SHOULD ALLOW HEAT INDEX READINGS TO CLIMB JUST ABOVE THE CENTURY MARK ALONG AND WEST OF THE MISSISSIPPI RIVER. STILL NOT SEEING ANY AREA OF 105 OR GREATER IN THE CALCULATED APPARENT TEMP GRIDS SO WILL NOT ISSUE ANY HEADLINES ATTM...HOWEVER WILL REISSUE SPS CALLING ATTENTION TO THE OPPRESSIVE CONDITIONS. TRUETT .LONG TERM...(TONIGHT THROUGH MONDAY) ISSUED AT 304 AM CDT TUE JUL 9 2013 THE SHORTWAVE THAT WAS OVER MONTANA EARLY THIS MORNING /PER WATER VAPOR IMAGERY AND ANALYSIS OF THE 1.5 PVU SFC/ WILL MOVE THROUGH THE NRN PLAINS TOWARDS THE WRN GRTLKS TONIGHT...DRAGGING A TRAILING CDFNT INTO THE NORTH CENTRAL CONUS. FORCING ALONG THE SFC FRONT WITHIN THE PRESENCE OF A MOIST AND UNSTABLE AIR MASS WILL SUPPORT TSRA DVLPMT ACROSS THE REGION TONIGHT. TSRA SHOULD CONGEAL INTO A LINE SOMEWHERE UPSTREAM AND THEN MOVE INTO THE CWA LATE TONIGHT OR EARLY TOMORROW MORNING. IF A LINE DEVELOPS OVERNIGHT THEN THERE MAY BE A CONCERN FOR DAMAGING WINDS ACROSS THE NRN CWA. THE EXISTENCE OF SUCH A LINE AND ITS OVERNIGHT TIMING WILL HAVE A LARGE IMPACT ON CONVECTIVE TRENDS AND POTENTIAL SEVERITY FOR THE REST OF THE DAY ON WEDNESDAY. ONE POSSIBILITY IS THAT THE OVERNIGHT CONVECTION COULD MOVE THROUGH THE ENTIRE CWA OVERNIGHT...THEREBY LIMITING THE OVERALL TSRA THREAT ON WED AFTN. ANOTHER POSSIBILITY IS THAT THE OVERNIGHT CONVECTION COULD MOVE THROUGH MOST OF THE CWA BEFORE PEAK HEATING ON WED AND THEN REINTENSIFY AS IT MOVES SEWD INTO AN AREA OF GREATER INSTABILITY...SHIFTING THE TSRA THREAT TO EARLIER IN THE DAY AND LIMITING THE SEVERE WX THREAT TO THE FAR SERN CWA. YET ANOTHER POSSIBILITY IS THAT THE OVERNIGHT CONVECTION COULD REACH ONLY THE EXTREME NRN PARTS OF THE CWA OVERNIGHT...IN WHICH CASE TSRA ALONG THE FRONT WOULD PROBABLY REINTENSIFY AND/OR REDEVELOP ACROSS THE CWA DURING THE AFTN AS THE ATMOSPHERE DESTABILIZES DURING PEAK HEATING. THE POP/WX FCST FOR TONIGHT AND TOMORROW GENERALLY REFLECTS A BLEND OF THESE POSSIBILITIES. HIGH PRESSURE BUILDING IN BEHIND THE CDFNT WILL PUSH THE BDRY THROUGH THE CWA ON WED/WED NIGHT...UNLESS OF COURSE THE SWD PUSH OF THE EFFECTIVE BDRY HAPPENED SOONER DUE TO PRIOR CONVECTION. ASSUMING THAT THE SYNOPTIC FNT IS APPROXIMATELY BISECTING THE CWA BY PEAK HEATING ON WED AND THAT LOW LEVEL MOISTURE HAS NOT BEEN SHUNTED SWD...INSOLATION AND MOISTURE POOLING AHEAD OF THE FRONT BENEATH FAVORABLE H7-H5 LAPSE RATES WILL CONTRIBUTE TO INCREASING INSTABILITY ACROSS THE SERN HALF OF THE CWA ON WED AFTN. SREF SHOWS HIGH PROBABILITIES OF AT LEAST 2000 J/KG OF SBCAPE IN THIS AREA AFTER 18Z HOWEVER THE 0-6 KM BULK SHEAR VALUES ARE ONLY AROUND 15-20 KTS /PERHAPS 25 KTS AT BEST/ ON THE MOST RECENT RUNS FROM HALF A DOZEN DIFFERENT MODELS. SEVERE WX IS POSSIBLE ON WED AFTN/EVE IF SUFFICIENT INSTABILITY CAN COMPENSATE FOR THE WEAKER SHEAR VALUES. THE CDFNT THEN STALLS NEAR THE MO/AR BORDER ON THU NIGHT/FRI WHILE THE WRN PORTION OF THE BDRY BECOMES REORIENTED AS A N-S WMFNT OVER THE CENTRAL PLAINS. THIS WILL LEAD TO COOLER TEMPERATURES ON THU/THU NIGHT ACROSS OUR AREA. ALTHOUGH THE CURRENT FCST FOR THU NIGHT REMAINS DRY...THERE ARE SEVERAL FACTORS THAT POINT TOWARDS MCS DVLPMT ACROSS SD OR NEB INCLUDING A CHANNEL OF VORTICITY...NW FLOW PATTN...STRONG H85 WAA...AND 925-850MB MOISTURE CONVERGENCE. SINCE CORFIDI VECTORS POINT STRONGLY SEWD...PCPN POTENTIAL WILL NEED TO BE MONITORED. MEANWHILE...THE SWRN CONUS HIGH PRESSURE CENTER WILL LIFT INTO THE SRN PLAINS WITH THE RIDGE AXIS TILTING TOWARDS THE GRTLKS IN RESPONSE TO A STRONG LOW PRESSURE SYSTEM MOVING THROUGH CANADA. THIS WOULD SUPPORT A RETURN OF WARMER WEATHER TO MISSOURI AND ILLINOIS LATE THIS WEEKEND AND EARLY NEXT WEEK. KANOFSKY && .AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON) ISSUED AT 1224 PM CDT TUE JUL 9 2013 PRIMARY CONCERN FOR THE NEXT 24 TO 36 HOURS IS THUNDERSTORM CHANCES. ISOLATED TO WIDELY SCATTERED STORMS ARE POSSIBLE AGAIN THIS AFTERNOON ACROSS MUCH OF THE AREA. STORMS MAY PRODUCE IFR VSBYS AND WIND GUSTS IN EXCESS OF 35KTS. AFTERNOON STORM ACTIVITY SHOULD SUBSIDE DURING THE EARLY EVENING...BUT ANOTHER ROUND OF STORMS IS EXPECTED DURING THE OVERNIGHT HOURS AS A COLD FRONT MOVES SOUTH OUT OF IOWA INTO MISSOURI AND SOUTHERN ILLINOIS. STRONG STORMS CAPABLE OF WIND GUSTS IN EXCESS OF 40KTS AND HEAVY RAIN REDUCING VSBYS TO IFR ARE POSSIBLE WITH THESE STORMS. THE COLD FRONT WILL DRIFT SOUTH OF THE I-70 CORRIDOR BY 18Z WEDNESDAY. AREAS SOUTH OF THE FRONT WILL REMAIN WARM AND UNSTABLE...WITH THE THREAT OF THUNDERSTORMS CONTINUING WEDNESDAY AFTERNOON. VFR FLIGHT CONDITIONS AND NORTHERLY FLOW IS EXPECTED BEHIND THE FRONT. SPECIFICS FOR KSTL... EXPECT VFR FLIGHT CONDITIONS AT LAMBERT THIS AFTERNOON AND THIS EVENING. THERE'S AN OUTSIDE CHANCE THAT AN ISOLATED THUNDERSTORM OR TWO MAY DEVELOP IN THE AREA THIS AFTERNOON...BUT THINK MOST OF THE ACTIVITY SHOULD BE EITHER SOUTH OF THE TERMINAL OVER THE EASTERN OZARKS OR OVER NORTHERN MISSOURI NEARER THE COLD FRONT. EXPECT A COMPLEX OF STORMS TO DEVELOP THIS EVENING OVER IOWA AND MOVE SOUTH WITH THE COLD FRONT...POSSIBLY AFFECTING THE TERMINAL BEFORE SUNRISE WEDNESDAY. UNSURE OF TIMING AND STRENGTH AT THIS TIME...BUT SOME GUSTY WINDS AND IFR CONDITIONS WILL CERTAINLY BE POSSIBLE WITH THE STRONGER STORMS. COLD FRONT SHOULD BE SOUTH OF THE TERMINAL BY 18Z WEDNESDAY BRINGING THE THUNDERSTORM THREAT TO AN END. CARNEY && .LSX WATCHES/WARNINGS/ADVISORIES... MO...NONE. IL...NONE. && $$ WFO LSX