Issued by NWS Central Illinois
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000 FXUS63 KILX 070132 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 832 PM CDT WED MAY 6 2009 .DISCUSSION... ISSUED 832 PM CDT WED MAY 6 2009 SCATTERED THUNDERSTORMS HAVE LINGERED ALONG OLD INSTABILITY AXIS NORTH OF PEORIA/BLOOMINGTON THIS EVENING. ACTIVITY IS BECOMING MORE ELEVATED WITH TIME...BUT SHOULD CONTINUE CONTINUE FOR A FEW MORE HOURS AS SATELLITE IMAGERY INDICATES MOISTURE ABOVE THE DE-COUPLING BOUNDARY LAYER. FURTHER SOUTH TOWARD I-72 AND BEYOND...MID LEVEL MOISTURE NOT QUITE AS RICH...SO MOST OF THE CONVECTION HAS DIED OUT WITH THE LOSS OF SURFACE HEATING. OUT WEST...THE NEXT UPPER WAVE IS ENTERING CENTRAL IOWA AND WILL BE BRUSHING ACROSS THE NORTHERN HALF OF ILLINOIS OVERNIGHT. THERE WILL BE ANOTHER RISK OF SCATTERED ELEVATED STORMS WITH THIS FEATURE...AND THE GOING FORECAST HAS THIS IN HAND PRETTY WELL. HAVE ALREADY TWEAKED PRE-06Z GRIDS FOR THE ACTIVITY THIS EVENING...AND WILL CONTINUE TO MONITOR RADAR TRENDS OVER IOWA FOR POSSIBLE ADJUSTMENTS AFTER MIDNIGHT. 04 && .AVIATION... ISSUED 615 PM CDT WED MAY 6 2009 SCT TSTMS DVLPD THIS AFTN NRN HALF OF IL WITHIN WK INSTABILITY AXIS...AND ISOLD STORMS CONT TO DVLP EARLY THIS EVE. WL INDICATE A TEMPO 00Z-02Z PIA...AND VCTS FOR SPI/BMI. PCPN WL LKLY CONT THRU THIS EVE OVR NRN IL WHERE SUFFICIENT MOISTURE ABV THE BNDRY LYR WL RESIDE FOR ELEVATED ACTVTY LATER ON. FURTHER S OVR CNTL IL...MOST OF THE CONVECTION SHUD EITHER DIE OUT OR BCM VRY ISOLD AT BEST. NEXT UPR WV WL MOV EWD FM WRN IA ACRS NRN IL AFT 06Z...SO WL INDICATE ANOTHER PD OF VCTS FOR PIA/BMI 07Z-10Z. SOME MDL DATA SUGGESTS THAT THE PCPN MAY EXTEND SWD AS FAR AS SPI/DEC...BUT THIS IS NOT CERTAIN AND WL KEEP POST-06Z PCPN OUT OF THESE AREAS FOR NOW. ANOTHER UPR WAVE AND SFC TROF EXPCTD TO COME INTO WRN IL AFT 18Z THU...BRINGING A PROB30 CHC FOR TSTMS TO PIA/SPI AFT 21Z. AS FOR FOG TNGT...SFC DWPTS ARE HIGHER THAN THEY WERE THIS TIME YESTERDAY AND NOT QUITE AS MUCH CLD CVR EXPCTD TNGT. WL THEREFORE INDICATE SOME TEMPO 5SM BR 08Z-12Z THU. 04 && .PREV DISCUSSION... ISSUED 239 PM CDT WED MAY 6 2009 SHORT TERM...TONIGHT THROUGH SATURDAY PRECIP COVERAGE AND TIMING THIS EVENING AND AGAIN FOR THE REMAINDER OF THE WEEK ARE THE MAIN FORECAST CHALLENGES. NW FRINGE OF MCS CLIPPED OUR SRN AND ERN COUNTIES LATE THIS MRNG BUT THAT SYSTEM HAS PUSHED OFF TO OUR EAST. MEANWHILE TO OUR NORTHWEST...SATELLITE AND PROFILER DATA INDICATES ANOTHER SHORTWAVE AFFECTING THE MISSOURI VALLEY WITH SCATTERED CONVECTION NOTED AHEAD OF THAT FEATURE IN IOWA AND SRN MN. DAYTIME HEATING ALONG WITH SOME WEAK INSTABILITY HAVE PRODUCED SOME ISOLD SHOWERS AND THUNDERSTORSM TO OUR NORTH AND WEST WITH THE BEST COVERAGE AXCRS NRN/NWRN IL. MODELS TEND TO KEEP PRECIP GOING AHEAD OF THE NRN STREAM WAVE THIS EVENING AND WITH INSTABILITY ON THE WANE AFTR SUNSET...WE SHOULD SEE AN OVERALL DECREASE IN COVERAGE OF SHOWERS LATE TNT. MODELS SUGGEST MORE OF A DIURNAL MODE TO ANY CONVECTION TMRW WITH SOME WEAK INSTABILITY AGAIN NOTED DURING THE AFTN AND EARLY EVENING HOURS. HOWEVER...THERE ARE SOME DIFFERENCES IN THE WAY MODELS HANDLE A POSSIBLE MCS PUSHING ACRS PARTS OF OUR AREA EITHER LATE THU NIGHT OR FRIDAY MRNG. THE NAM IS MUCH MORE BULLISH WITH THIS FEATURE WITH SOME FAIRLY DECENT 850 THETA-E ADVECTION NOTED TO OUR SOUTH ON THE NOSE OF THE LOW LEVEL JET...WHILE THE GFS DOES NOT DEVELOP MUCH CONVECTION TO OUR SOUTH THU NIGHT...IN FACT THE MODEL TENDS TO BECOME VERY AGGRESSIVE WITH THE DEVELOPMENT OF A CONVECTIVE COMPLEX FRIDAY MRNG. FOR NOW WL TEND TO SIDE MORE WITH THE NAM-WRF IN THE DEVELOPMENT OF A COMPLEX TO OUR SOUTH THU NIGHT INTO FRIDAY MRNG. AFTER THAT...MODELS SUGGEST A SOUTHWARD DISPLACEMENT IN THE LOW LEVEL BAROCLINIC ZONE WHICH WOULD INDICATE THE BEST CHANCES FOR ORGANIZED CONVECTION WILL BE TO THE SOUTH OF OUR AREA OVER THE WEEKEND. PREVIOUS FORECAST HAD TRENDED IN THAT DIRECTION STARTING ON SATURDAY AND WILL CONTINUE WITH THAT TREND AS WELL. LONG TERM...SUNDAY THROUGH WEDNESDAY LATEST ECWMF SIDING MORE WITH THE OPERATIONAL GFS IN SHIFTING THE MAIN BAROCLINIC ZONE AND CONVECTION CHANCES TO OUR SOUTH LATE SATURDAY INTO SUNDAY WITH CANADIAN HIGH PRESSURE SETTLING IN FOR THE RMDR OF THE WEEKEND. RATHER FAST ZONAL FLOW STILL FORECAST ACRS THE LOWER 48 FOR THIS PERIOD SO CONFIDENCE WITH TIMING OF SHORTWAVES AND PRECIP EVENTS INTO OUR AREA NOT THAT GREAT. UPPER LEVEL RIDGING SHOULD BUILD ACRS THE AREA INTO EARLY NEXT WEEK AHEAD OF THE NEXT SIGNIFICANT WAVE AND COLD FRONT FOR WED INTO WED NIGHT. RAIN CHANCES START AS EARLY AS TUE NIGHT IN THE WARM ADVECTION PATTERN AHEAD OF THE SHORTWAVE. RAIN CHANCES WL CONTINUE INTO WED NIGHT AS THE AND WL CONTINUE ACTUAL COLD FRONT IS EXPECTED TO PUSH ACRS THE AREA THEN. SMITH && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
