976  
FXUS63 KILX 201128  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
628 AM CDT THU SEP 20 2018  
   
SHORT TERM
 
(TODAY THROUGH FRIDAY)  
ISSUED AT 317 AM CDT THU SEP 20 2018  
 
MAJORITY OF THE SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE NEXT  
WEATHER SYSTEM TO IMPACT CENTRAL IL ARE CURRENTLY NORTH OF THE  
AREA. WINDS INCREASING OUT OF THE SOUTHWEST TODAY WILL PICK UP AND  
PUSH THE DIFFUSE SFC REFLECTION OF A WARM FRONT FURTHER NORTH  
QUICKLY TODAY. CENTRAL IL WILL REMAIN FIRMLY IN A WARM SECTOR  
ENVIRONMENT, WITH HOT AND HUMID AIR IN PLACE. TEMPS WILL WARM  
QUICKLY TODAY, WITH GUSTY SOUTHWESTERLY WINDS. EARLY LLVL  
MOISTURE WILL RESULT IN SOME HEAT INDEXES IN THE UPPER 90S/LOW  
100S BY THE EARLY AFTERNOON BEFORE MIXING OUT TO A CERTAIN EXTENT.  
WITH THE STRONG WARM AIR ADVECTION MOVING INTO THE REGION,  
DIURNAL DEVELOPMENT WILL BE ISOLATED AT BEST WITH RATHER LACKING  
LAPSE RATES. HOWEVER, YESTERDAYS AFTERNOON ACTIVITY WAS ENOUGH TO  
WARRANT A VERY LOW POP AHEAD OF THE APPROACHING COLD FRONT LATER  
TONIGHT.  
 
THE NEXT LOW WILL MOVE ACROSS THE PLAINS AND INTO THE MIDWEST  
TONIGHT AND INTO TOMORROW MORNING, DRAGGING A COLD FRONT THROUGH  
THE REGION. EVEN THIS CLOSE TO THE ARRIVAL OF THE FRONT, THE  
MODELS ARE STILL HAVING INCONSISTENT TIMING. THE GFS IS MORE QUICK  
WITH THE PASSAGE OF THE BOUNDARY, THE ECMWF AND NAM SLIGHTLY  
SLOWER. BOTH, HOWEVER, BRING THE FRONT THROUGH MAINLY IN THE  
OVERNIGHT HOURS, LIMITING THE CONVECTIVE ACTIVITY OVER CENTRAL IL  
AND ALSO THE SEVERE WEATHER THREAT. WITH THE POTENTIALLY SLOWER  
PROGRESSION OF THE BOUNDARY, THE POTENTIAL FOR SOME SEVERE WEATHER  
MAY OCCUR TOMORROW ON A REFIRE OF THE BOUNDARY SOUTH OF I-70. THAT  
AREA IS IN A MARGINAL RISK FOR FRIDAY AFTERNOON. IN THE MEANTIME,  
MUCH OF THE INITIAL CONVECTION ALONG AND AHEAD OF THE BOUNDARY  
FALLS APART IN THE CAMS AS THE PRECIP APPROACHES THIS EVENING.  
 
EVEN SO, BUFKIT SOUNDINGS HAVE ENOUGH WIND BELOW 5KFT TO BRING  
SOME VERY GUSTY WINDS WITH EVEN WEAKER SHOWERS THIS EVENING,  
SHOULD THEY TRANSLATE TO THE SURFACE. TEMPS TOMORROW CONSIDERABLY  
COOLER BEHIND THE BOUNDARY AND DIMINISHING PRECIP. LOCATION OF  
THAT FRONT IS QUESTIONABLE, AND COULD RESULT IN SOME CONTINUED HOT  
AND MUGGY CONDITIONS SOUTH OF A LINE ROUGHLY FROM EFFINGHAM TO  
PARIS.  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 317 AM CDT THU SEP 20 2018  
 
FRONT STALLS SOMEWHAT IN THE OHIO RIVER VALLEY, BUT HOLDS MOST OF  
THE PRECIP CHANCES SOUTH OF THE REGION. WEEKEND FORECAST IS THEN  
LOOKING INCREASINGLY DRIER AND TEMPS MUCH COOLER ON SATURDAY. BY  
SUNDAY, HOWEVER, THOSE MIDLEVELS THAT DID NOT QUITE GET THE COOLER  
TEMPS WITH THE FRONT START TO DOMINATE AGAIN, AND SOUTHWESTERLY  
FLOW HELPS PICK UP YET ANOTHER WARMING TREND FOR TEMPS IN THE  
UPPER 70S BY SUNDAY IN WESTERN IL...SPREADING ACROSS CENTRAL IL  
FOR MONDAY.  
 
ANOTHER PATTERN SHIFT TO MORE FALL LIKE TEMPERATURES SETTING UP  
FOR EARLY IN THE WEEK. MODELS HAVING TROUBLE WITH RESOLVING THE  
POPS/SPEED OF THE PRECIP AHEAD OF THE SHOWERS OVERNIGHT MONDAY  
INTO TUESDAY NIGHT. BUT HIGH TEMPERATURES ON THE OTHER SIDE OF THE  
PRECIP DROP INTO THE LOW 70S BY MIDWEEK.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)  
ISSUED AT 615 AM CDT THU SEP 20 2018  
 
PATCHY 5-6SM IN GROUND FOG TIL 13Z, OTHERWISE, VFR CONDITIONS  
EXPECTED THIS FORECAST PERIOD. MAIN FORECAST CHALLENGE WILL BE  
WITH COVERAGE OF ANY TSRA TODAY AND ESPECIALLY AFTER 03Z TONIGHT  
AS A COLD FRONT PUSHES TOWARDS OUR AREA. SCATTERED CUMULUS EXPECTED  
TODAY WITH BASES AROUND 5000 FEET WITH FORECAST SOUNDINGS INDICATING  
SOUTHERLY WINDS SHOULD START TO INCREASE BY LATE MORNING INTO THE  
AFTERNOON HOURS WITH GUSTS UP TO AROUND 20 KTS AT PIA, BMI AND SPI  
WITH DEC AND CMI HAVING THE GUSTS MAINLY THIS AFTERNOON. NOT MUCH,  
IF ANY DROP OFF IN THE GUSTY SOUTH WINDS TONIGHT AS A COLD FRONT  
APPROACHES THE AREA FROM THE WEST. IT APPEARS COVERAGE OF ANY TSRA  
THIS AFTERNOON WILL ONCE AGAIN BE TOO LIMITED TO INCLUDE IN THE  
TAFS.  
 
WILL CONTINUE TO INCLUDE LLWS IN THE WESTERN TAF SITES THIS EVENING  
WITH 1500-2000 FOOT WINDS FROM THE SOUTH TO SOUTHWEST INCREASING  
TO 45 KTS. HOWEVER, AT THE SAME TIME, CONVECTION CHANCES AHEAD OF  
THE COLD FRONT WILL START TO INCREASE AFTER 03Z WEST OF THE MISSISSIPPI  
RIVER. HOWEVER, LATEST MODEL GUIDANCE CONTINUES TO WEAKEN THE BAND OF  
STORMS BEFORE IT GETS INTO OUR AREA LATE TONIGHT SO WILL NOT INCLUDE  
IN THIS SET OF TAFS AND HIGHLIGHT THE LLWS THREAT IN PIA, BMI AND SPI  
LATE THIS EVENING.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...HJS  
LONG TERM...HJS  
AVIATION...SMITH  
 
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