128 FXUS63 KLSX 302343 AFDLSX AREA FORECAST DISCUSSION...UPDATED AVIATION NATIONAL WEATHER SERVICE ST LOUIS MO 643 PM CDT THU AUG 30 2012 .SHORT TERM... ISSUED AT 316 PM CDT THU AUG 30 2012 (TONIGHT) LEADING EDGE OF RAIN ASSOCIATED WITH ISAAC WILL BEGIN TO ENTER S SECTIONS OF THE AREA OVERNIGHT. N EDGE OF RAIN CURRENTLY OVER CENTRAL AR AND EXTRAPOLATION OVER THE LAST FEW HOURS SUGGESTS RAIN COULD MOVE INTO FAR S SECTION OF OUR FA AS EARLY AS 03Z...HOWEVER THINK DRY AIR N OF SYSTEM MAY SLOW DOWN THE NWD EXPANSION INTO OUR AREA OVERNIGHT. AS A RESULT...HAVE PLACED N EDGE OF RAIN JUST S OF THE I-70 CORRIDOR BY DAYBREAK...WITH POPS INCREASING TO AROUND 50% OVER OUR S COUNTIES BY THAT TIME. TRUETT && .LONG TERM... ISSUED AT 316 PM CDT THU AUG 30 2012 (FRIDAY THROUGH SUNDAY) TROPICAL STORM ISAAC CONTINUES TO MOVE SLOWLY NWWD THROUGH NRN LA. NHC FORECAST TRACK STILL HAS THE WEAKENING REMNANT OF ISAAC MOVING INTO SWRN MO FRIDAY EVENING THEN NEWD THROUGH OUR FORECAST AREA SAT AND SAT NGT...FROM NEAR JEF TO 3LF. NAM MODEL APPEARS TOO WEAK AND TOO FAR WEST WITH ISAAC. PREFER THE GFS AND ECMWF MODELS WHICH ARE INITIALLY A LITTLE WEST OF THE NHC FORECAST TRACK THEN BRINGS ISAAC NEWD TO STL BY 12Z SUN. STILL SOME UNCERTAINTY WITH THE EXACT TRACK OF ISAAC AS IT MOVES NWD TOWARDS THE UPPER LEVEL RIDGE OVER OUR AREA. RAIN SHOULD SPREAD NWD THROUGH OUR ENTIRE AREA ON FRI AS SLY WINDS AHEAD OF ISAAC BRING ABUNDANT MOISTURE INTO OUR AREA. WIDESPREAD RAINFALL WILL CONTINUE FRI NGT AND SAT. WITH PRECIPITABLE WATER VALUES QUITE HIGH...MAY BE NEAR 2 INCHES AND DEEP WARM CLOUD LAYER DEPTH RAINFALL RATES MAY BE HIGH. WITH HIGH RAINFALL RATES AND A PROLONGED PERIOD OF RAINFALL THERE MAY BE URBAN FLOODING AND SMALL CREEKS AND STREAMS MAY ALSO FLOOD SAT OR SAT NGT NEAR THE END OF THIS POTENTIALLY HEAVY RAINFALL EVENT. WILL CONTINUE THE HYDROLOGIC OUTLOOK FOR FRI NGT AND SAT WHEN THE HEAVIEST RAINFALL IS EXPECTED. TOTAL RAINFALL AMOUNTS OF 3 TO 5 INCHES ARE STILL EXPECTED WITH LOCALLY HIGHER AMOUNTS. WILL HOLD OFF ON AN FFA AS THE ANTECEDENT CONDITIONS ARE DRY WITH RIVERS AND STREAMS RUNNING QUITE LOW. THE RAINFALL WILL CONTINUE SAT NGT AND SUN BUT SHOULD BECOME LIGHTER AS THE POST TROPICAL REMNANT LOW MOVES EWD INTO SRN IL AND TAPERS OFF FROM W TO E. HIGH TEMPERATURES WILL BE COOLER FRI THROUGH SUN DUE TO LOW LEVEL CLOUD COVER AND PRECIPITATION. GKS (SUNDAY NIGHT - THURSDAY) ISAAC'S REMNANTS WILL BE SLOW TO MOVE OUT SUNDAY NIGHT WITH SFC LOW PER LATEST NHC GUIDANCE STILL IN EASTERN ILLINOIS. EXPECT CLOUDS TO BE SLOW TO MOVE OUT...ESPECIALLY OVER OUR EASTERN CWFA. ALSO KEPT SLIGHT CHANCE SHOWERS OVER FAR EAST FOR ANY LINGERING EFFECTS FROM THE SLOW MOVING ISAAC. MONDAY/TUESDAY SHOULD BE QUITE A BIT WARMER THAN THIS UPCOMING WEEKEND AS CLOUDS DECREASE...850-HPA TEMPS INCREASE TO BETWEEN ROUGHLY 18 AND 22 C...AND 500-HPA HEIGHTS RISE AS THE MIDLEVEL FLOW REGIME TRANSITIONS TO A QUASI-ZONAL/WNW FLOW PATTERN. WENT ABOVE CENTRAL REGION INIT WITH RESPECT TO TEMPERATURES...ESPECIALLY FOR HIGHS MON/TUE. ASSOCIATED MEDIUM RANGE MODELS ARE FORECASTING SUBTLE SHORTWAVES/VORTICITY MAXIMA TO QUICKLY TRANSVERSE THE MID/UPPER MISSISSIPPI RIVER VALLEY. GIVEN MODEL TO MODEL TEMPORAL CONSISTENCIES...ELECTED TO KEEP SHOWER/THUNDERSTORM CHANCES THROUGH THURSDAY BELOW CHANCE CATEGORY. TEMPERATURES WILL COOL SLIGHTLY WED/THU WITH AN EXPECTED INCREASE IN CLOUD COVER. HOWEVER...DID NOT GO QUITE AS COOL AS INITIALIZATION DUE TO THE AFOREMENTIONED UNCERTAINTY IN POPS/TIMING OF INDIVIDUAL SHORTWAVES. UPPER-LEVEL FLOW REGIME LOOKS TO GET MORE AMPLIFIED LATE IN THE PERIOD WITH MORE NORTHERLY FLOW DEVELOPING...POSSIBLY SIGNIFYING A TRANSITION TO A COOLER WX PATTERN. GOSSELIN && .AVIATION... ISSUED AT 627 PM CDT THU AUG 30 2012 HIGH CLOUDS WILL BE ADVANCING NORTHWARD INTO THE AREA THIS EVENING AHEAD OF ISAAC...WITH EXTENSIVE MID/HI CLOUD COVER BY DAYBREAK ON FRIDAY. IT STILL LOOKS REASONABLE THAT THE LEADING/ NORTHERN EDGE OF THE RAIN SHIELD/RAIN BANDS WITH ISAAC WILL ADVANCE TO NEAR THE INTERSTATE 70 CORRIDOR BY MID-MORNING ON FRIDAY AND INTO NORTHERN MO AND WEST CENTRAL IL BY MID AFTERNOON. THE RAINFALL INTENSITY IS EXPECTED TO RAMP UP ON FRIDAY AFTERNOON INTO THE EVENING WITH A CONCURRENT DETERIORATION IN VSBYS/CIGS. THERE COULD BE SOME OCCASIONAL IFR CONDITIONS DURING THE LATE AFTERNOON BUT BELIEVE MORE PERSISTENT IFR WILL HOLD OFF UNTIL FRIDAY EVENING. EAST-SOUTHEAST SURFACE WINDS WILL ALSO INCREASE AND BECOME GUSTY IN THE AFTERNOON. SPECIFICS FOR KSTL... VFR CONDITIONS STILL EXPECTED TO PREVAIL THROUGH DAYBREAK FRIDAY WITH HIGH CLOUDS SPREADING INTO THE AREA TONIGHT IN ADVANCE OF ISAAC. THE ONSET OF RAIN BY MID-MORNING FRIDAY STILL LOOKS ON TRACK. CONDITIONS SHOULD BEGIN WITH VFR VSBYS/CIGS...HOWEVER FLIGHT CONDITIONS SHOULD DETERIORATE TO MVFR ON FRIDAY AFTERNOON AND EVENING AS HEAVIER RAIN MOVES INTO THE REGION. THERE COULD BE SOME OCCASIONAL IFR CONDITIONS DURING THE LATE AFTERNOON BUT BELIEVE MORE PERSISTENT IFR WILL HOLD OFF UNTIL FRIDAY EVENING. EAST-SOUTHEAST SURFACE WINDS WILL ALSO INCREASE AND BECOME GUSTY IN THE AFTERNOON. GLASS && .LSX WATCHES/WARNINGS/ADVISORIES... MO...NONE. IL...NONE. && $$ WFO LSX