005  
FXUS63 KILX 242011  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
311 PM CDT FRI OCT 24 2014  
   
SHORT TERM
 
(TONIGHT)  
ISSUED AT 309 PM CDT FRI OCT 24 2014  
 
19Z/2PM SATELLITE IMAGERY SHOWS LOW CLOUDS THAT PERSISTED FOR MUCH  
OF THE DAY ACROSS WEST-CENTRAL ILLINOIS HAVE FINALLY DISSIPATED,  
WITH JUST ONE SMALL PATCH REMAINING FROM SOUTH OF LINCOLN TO NEAR  
TAYLORVILLE. BASED ON SATELLITE TRENDS, THIS PATCH WILL DISSIPATE  
OVER THE NEXT HOUR OR SO AS WELL, LEADING TO MOSTLY CLEAR SKIES LATE  
THIS AFTERNOON INTO THE EARLY EVENING. MAIN SHORT-TERM FORECAST  
CONCERN WILL BE THE POTENTIAL RE-DEVELOPMENT OF LOW CLOUDS/FOG  
TONIGHT AS A WEAK TROUGH OF LOW PRESSURE MOVES THROUGH THE AREA.  
WHILE THE OVERALL DEPTH OF THE ATMOSPHERE WILL BE VERY DRY, A  
SHALLOW SURFACE-BASED MOIST LAYER WILL REMAIN IN PLACE. WITH NO  
DEEP-LAYER MOISTURE TO WORK WITH, PRECIP IS NOT EXPECTED TO DEVELOP  
ALONG THE TROUGH DESPITE THE NAM HINTING AT SOME OVERNIGHT. AS WINDS  
BECOME LIGHT/VARIABLE AND CLOUD COVER ASSOCIATED WITH THE PASSING  
TROUGH BEGINS TO CLEAR FROM NORTHWEST TO SOUTHEAST AFTER MIDNIGHT,  
FOG WILL BEGIN TO DEVELOP. HRRR IS SHOWING WIDESPREAD FOG ONCE  
AGAIN FORMING ACROSS CENTRAL/EASTERN IOWA, THEN SPREADING INTO THE  
ILLINOIS RIVER VALLEY TOWARD DAWN. AS A RESULT, WILL CARRY AREAS OF  
FOG ALONG/WEST OF THE ILLINOIS RIVER, WITH PATCHY FOG AS FAR EAST AS  
CHAMPAIGN/DANVILLE. DUE TO CLOUD COVER AND LIGHT SOUTHERLY WINDS,  
LOW TEMPERATURES WILL BE QUITE A BIT WARMER THAN IN RECENT NIGHTS,  
WITH READINGS REMAINING IN THE LOWER TO MIDDLE 50S.  
 

 
   
LONG TERM
 
(SATURDAY THROUGH FRIDAY)  
ISSUED AT 309 PM CDT FRI OCT 24 2014  
 
SATURDAY WILL START OFF WITH SOME MORNING FOG, MAINLY N OF I-70. THE  
FOG SHOULD BURN OFF AROUND MID-MORNING, AS A COLD FRONT PUSHES EAST  
ACROSS IL. SOME COOLER AIR ASSOCIATED WITH THE FRONT WILL BE MAINLY  
CONFINED TO NORTHERN IL, WITH OUR 850MB TEMPS STILL REMAINING THE  
12-14C RANGE IN THE POST-FRONTAL AIRMASS. DRY-ADIABATIC WARMING OF  
THAT LAYER TO THE SURFACE, COUPLED WITH SOME SUNSHINE SHOULD HELP  
PUSH HIGH TEMPS INTO THE LOW 70S N OF I-74 WITH UPPER 70S S OF  
I-70. NW WINDS WILL STILL DEVELOP BEHIND THE FRONT, SO A BRIEF  
CHILL MAY BE ADDED TO THE AIR AT TIMES.  
 
MID LEVEL WARMING WILL DEVELOP SATURDAY NIGHT INTO SUNDAY, AS 850MB  
TEMPS CLIMB TOWARD +16C. THAT WARM LAYER WILL LINGER INTO MONDAY.  
SOUTHERLY WINDS WILL DEVELOP SUNDAY AFTERNOON ONCE THE SURFACE RIDGE  
AXIS MOVES EAST OF IL, SO HIGHS SHOULD ONCE AGAIN CLIMB INTO THE 70S  
ACROSS THE BOARD. ON MONDAY, A FEW 80 DEGREE READINGS WILL POSSIBLE  
ON MONDAY ACROSS SOUTHWEST AND SOUTHEAST PORTIONS OF THE FORECAST  
AREA, WHICH WOULD BE NEARLY 20 DEGREES ABOVE NORMAL FOR LATE  
OCTOBER. RECORD HIGHS FOR MONDAY ARE IN THE MID 80S AND CURRENTLY  
APPEAR SAFE.  
 
A LONG WAVE TROUGH IS FORECAST TO MOVE ACROSS THE NORTHERN  
PLAINS ON MONDAY NIGHT, WITH COLD FRONT PROGRESSING ACROSS IL  
TUESDAY MORNING AND EARLY AFTERNOON. THE ECMWF INDICATES A MORE  
DYNAMIC SYSTEM DEVELOPING IN THE WESTERN GREAT LAKES ON TUESDAY,  
WHILE THE GFS REMAINS A BIT MORE PROGRESSIVE AND LESS STRONG WITH  
THE FRONTAL PASSAGE IN OUR AREA OF IL. WE DID MAINTAIN WIDESPREAD  
CHANCE POPS MONDAY NIGHT, AS MOISTURE POOLING AND LIFT STILL APPEAR  
TO BE SUFFICIENT A BAND OF RAIN TO AFFECT CENTRAL IL. WE CONTINUED  
THE LIKELY POPS IN SE ILLINOIS FOR TUESDAY, BUT CHANCES SHOULD  
DIMINISH TUE AFTERNOON AS THE MAIN FORCING FOR PRECIP DEPARTS INTO  
INDIANA, AND DRY AIR QUICKLY FILTERS INTO THE AREA ALOFT.  
 
A SIGNIFICANT COOL DOWN IS AGREED UPON BY THE GFS AND ECMWF FOR  
TUESDAY AND TUESDAY NIGHT, AS 850MB TEMPS PLUMMET TO 0 TO -3C BY  
MIDDAY WEDNESDAY. THAT WILL BRING TEMPS BACK BELOW NORMAL FOR HIGHS  
WED, WITH UPPER 50S NORTH OF I-74, WITH LOW 60S SOUTH NEAR  
JACKSONVILLE TO LAWRENCEVILLE.  
 
ANOTHER COLD FRONT IS INDICATED FOR THURSDAY, WITH BETTER AGREEMENT  
ON TIMING OF THE FRONT BETWEEN THE GFS AND ECMWF. CONFIDENCE IS  
INCREASING THAT A BAND OF LIGHT RAIN SHOWERS MAY ACCOMPANY THAT  
FRONT. SO LOW CHANCES FOR RAIN WAS ADDED TO THE THURS FORECAST,  
MAINLY FROM THE ILLINOIS RIVER TO I-55.  
 
THE GFS IS A ABOUT 4-5 DEGREES COLDER THAN THE ECMWF BEHIND THE  
FRONT, WITH 850MB READINGS IN THE -2 TO -4C RANGE FRIDAY AFTERNOON.  
WE WILL CONTINUE WITH THE COOLING TREND FOR LATE WEEK. SOME FREEZING  
TEMPS COULD DEVELOP FOR FRIDAY NIGHT N OF I-74 IF THE GFS SCENARIO  
PANS OUT.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)  
ISSUED AT 1257 PM CDT FRI OCT 24 2014  
 
LOW CLOUDS ARE RAPIDLY DISSIPATING ACROSS THE AREA EARLY THIS  
AFTERNOON, WITH 1730Z VISIBLE SATELLITE IMAGERY SHOWING ONE  
PERSISTENT BAND FROM KGBG TO KTAZ. BASED ON SATELLITE TRENDS,  
WILL HOLD ON TO IFR CEILINGS AT KSPI FOR ONE MORE HOUR BEFORE  
CLEARING THINGS OUT BY 19Z. ONCE THESE CLOUDS DISSIPATE, ONLY  
FEW-SCT DIURNAL CU AND HIGH/THIN CIRRUS WILL BE NOTED FOR THE  
BALANCE OF THE DAY. MAIN AVIATION QUESTION WILL BE HOW LOW  
CEILINGS WILL GO TONIGHT AS TROUGH AXIS APPROACHES FROM THE  
NORTHWEST. NAM FORECAST SOUNDINGS AND LATEST HRRR BOTH SUGGEST AT  
LEAST MVFR CEILINGS SPREADING IN FROM THE NW BETWEEN 02Z AND 05Z.  
THIS BAND OF LOW CLOUDS WILL BEGIN CLEARING OUT AFTER MIDNIGHT,  
WHICH WILL LIKELY LEAD TO FOG DEVELOPMENT TOWARD DAWN. GIVEN A  
SIMILAR AIRMASS TO LAST NIGHT AND WINDS EXPECTED TO BECOME  
LIGHT/VARIABLE IN THE VICINITY OF THE TROUGH, HAVE REDUCED VISBYS  
TO BETWEEN 1 AND 3 MILES AT THE TERMINALS. ONCE THE TROUGH PASSES,  
WINDS WILL VEER TO THE W/NW AND ANY LOW CLOUDS/FOG WILL CLEAR OUT  
BY SATURDAY MORNING.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...BARNES  
LONG TERM...SHIMON  
AVIATION...BARNES  
 
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