Issued by NWS Central Illinois
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000 FXUS63 KILX 201119 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 619 AM CDT SAT SEP 20 2008 .DISCUSSION... ISSUED 215 AM CDT SAT SEP 20 2008 WATER VAPOR IMAGERY SHOWING WEAK UPPER DISTURBANCE ACROSS SOUTH CENTRAL MISSOURI OVERNIGHT. SHOWERS AND THUNDERSTORMS DEVELOPED WITH THIS FEATURE...AND A FEW SHOWERS HAVE PIVOTED NORTHWARD TOWARD THE SALEM AND FLORA AREAS OF SOUTH CENTRAL ILLINOIS. OUTFLOW BOUNDARY FROM THIS FEATURE HAS PUSHED ALL THE WAY NORTH TO A HAVANA TO TUSCOLA LINE. MAIN FORECAST ISSUES WILL BE WITH RAIN CHANCES OVER THE NEXT COUPLE DAYS. SHORT TERM...TODAY THROUGH MONDAY... UPPER LOW EXPECTED TO VERY SLOWLY LIFT NORTHEAST ACROSS SOUTHERN ILLINOIS THIS WEEKEND. WITH RELATIVELY COOL AIR ALOFT FROM THE UPPER LOW...A FEW SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE DURING THE AFTERNOON HEATING. THIS WILL BE MAINLY ACROSS THE SOUTHERN PORTIONS OF THE CWA ON SATURDAY...AND OVER THE ENTIRE AREA ON SUNDAY. RAIN TOTALS EXPECTED TO BE RELATIVELY LIGHT...DESPITE THE MORE BULLISH TOTALS SHOWN BY THE GFS ON SUNDAY. PRECIP THREAT TO DIMINISH SUNDAY NIGHT...AS UPPER LEVEL HIGH PRESSURE AXIS SHIFTS EAST ACROSS THE CENTRAL PART OF NORTH AMERICA. WENT CLOSE TO FWC GUIDANCE ON TEMPERATURES TODAY AND TONIGHT...BUT USED THE MAV NUMBERS FOR THE SOUTHEAST CWA...WHERE CLOUD COVER WILL BE MORE PREVALENT. MAV GUIDANCE USED FOR SUNDAY. LONG TERM...TUESDAY AND WEDNESDAY... NEXT FEATURE OF INTEREST WILL BE A STORM SYSTEM MOVING ACROSS THE NORTHERN PLAINS EARLY IN THE WEEK. NEW GFS HAS THIS SYSTEM CROSSING ILLINOIS ON WEDNESDAY. THIS MAY BE A BIT FAST...WITH HIGH PRESSURE ANCHORED ON THE EAST COAST. RAINFALL WITH THIS SYSTEM IS EXPECTED TO BE JUST BEYOND THE EDITABLE FORECAST PERIOD. GEELHART && .AVIATION... ISSUED 619 AM CDT SAT SEP 20 2008 UPPER LOW OVR SERN MO WILL MOVE SLOWLY NWD INTO WEST-CENTRAL IL BY 12Z SUN. A FEW PATCHES OF SHOWERS ON THE NE PERIPHERY OF THE LOW WILL COME CLOSE TO SPI AND PERHAPS DEC BEFORE 15Z TODAY BEFORE DIMINISHING. THEN EXPECT REGENERATION OF CONVECTION AFT 18Z ON A SCT BASIS...BUT LESS NUMEROUS TWD PIA/BMI. AS THE CENTER OF THE UPPER LOW APPROACHES AFT 06Z SUN...NOCTURNAL CONVECTION WILL INCREASE NEAR SPI/DEC AS WAS THE CASE OVR SERN MO THIS MORNING. REGARDING CIGS/VSBYS...CIGS WILL SLOWLY DECREASE WITH INCREASING ATMOSPHERIC MOISTURE...BUT SHOULD REMAIN VFR OUTSIDE OF PRECIP THRU 00Z SUN. MVFR CIGS WILL THEN SPREAD NWD AND ENVELOP AT LEAST SPI/DEC. AFTER SOME PERIODIC VSBYS 3-5SM EARLY TODAY...EXPECT P6SM UNTIL AFT 06Z SUN...WHEN MVFR VSBYS WILL LIKELY BE MORE WIDESPREAD THAN THIS MORNING. WEAK SURFACE PATTERN WILL RESULT IN LGT/VRBL SFC FLOW THRU THE TAF PD. 04 && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
