141  
FXUS63 KILX 221746  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
1246 PM CDT FRI OCT 22 2021  
   
SYNOPSIS
 
 
ISSUED AT 1053 AM CDT FRI OCT 22 2021  
 
A BUSY WEEK IS FORTHCOMING AS A PAIR OF STRONG AUTUMN STORM  
SYSTEMS LIFT ACROSS CENTRAL ILLINOIS. PERIODS OF HEAVY RAINFALL  
AND STRONG THUNDERSTORMS ARE ANTICIPATED ON SUNDAY, AND AGAIN ON  
WEDNESDAY. MEANWHILE, TEMPERATURES WILL REMAIN ON THE MILD SIDE AS  
FROST AND FREEZE CONCERNS DELAY UNTIL EARLY NOVEMBER.  
 

 
   
UPDATE
 
 
ISSUED AT 1053 AM CDT FRI OCT 22 2021  
 
SATELLITE IMAGERY SHOWS BREAKS IN THE LOW CLOUDINESS TOWARD THE  
ILLINOIS RIVER VALLEY AND NORTHWEST, THOUGH THE BREAKS ARE FILLING  
IN WITH CUMULUS SO EVEN THERE ANTICIPATE MORE CLOUDS THAN SUN  
THROUGH THIS AFTERNOON. ESPECIALLY EAST OF I-55, LOW CLOUDS ARE  
MORE ENTRENCHED WITH EVEN PERIODS OF STEADY DRIZZLE OBSERVED THIS  
MORNING. DRIZZLE, CURRENTLY MOST PRONOUNCED FROM NEAR CHAMPAIGN  
DOWN TOWARD DECATUR AND TAYLORVILLE, WILL GRADUALLY MOVE OFF TO  
THE EAST OVER THE NEXT FEW HOURS BUT WITH COOL TEMPERATURES AND  
MOSTLY CLOUDY SKIES CONTINUING.  
 
A FEW MINOR CHANGES WERE MADE INCLUDING TO BUMP UP CLOUD COVER  
THROUGH THIS EVENING, BUT OTHERWISE THE GOING FORECAST LOOKS GOOD.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 237 AM CDT FRI OCT 22 2021  
 
LOW-LEVEL STRATUS WILL KEEP SKIES MURKY THIS MORNING AS PARCELS  
REMAIN ADEQUATELY SATURATED IN THE LOWEST 5 KFT. THIS IS A GOOD  
DRIZZLE PATTERN WITH THE ABSENCE OF CLOUD ICE AND INCREASING OMEGA  
AHEAD OF A MID-LEVEL WAVE EMBEDDED IN CYCLONIC FLOW. PATCHY  
DRIZZLE WILL END FROM WEST TO EAST THIS AFTERNOON AS A WEDGE OF  
LOW-LEVEL DRY AIR ADVECTS ACROSS THE ILLINOIS RIVER VALLEY.  
STILL, SKIES WILL REMAIN MOSTLY CLOUDY LATER THIS AFTERNOON INTO  
EARLY EVENING AS ADDITIONAL WAVES RIPPLE THROUGH MID-LEVEL FLOW.  
THIS ALL ADDS UP TO A SEASONABLY COOL DAY, WITH AFTERNOON HIGHS  
STRUGGLING TO WARM ABOVE THE MID 50S.  
 
THERE IS A LOW-END CHANCE FOR PATCHY FROST LATE TONIGHT, MAINLY  
ACROSS THE NORTHERN THIRD OF THE STATE. IF SKIES BECOME CLEAR FOR  
A COUPLE HOURS OVERNIGHT, TEMPERATURES WILL FALL INTO THE MIDDLE  
30S, IF NOT LOWER. THERE IS REASON TO BELIEVE, HOWEVER, THAT HIGH  
CLOUDS WILL LINGER ALL NIGHT AS AN UPPER-LEVEL SPEED MAX MOVES  
ACROSS THE REGION. THIS WOULD MITIGATE THE FROST THREAT. BOTTOM  
LINE, WE'RE NOT ADVERTISING FROST/FREEZE HEADLINES THIS FAR SOUTH  
ACROSS CENTRAL ILLINOIS WHERE OVERNIGHT LOWS ARE FORECAST TO BE IN  
THE UPPER 30S TO LOWER 40S; THE GALESBURG AND LACON AREAS BEAR  
WATCHING, THOUGH.  
   
LONG TERM
 
(SATURDAY THROUGH THURSDAY)  
ISSUED AT 237 AM CDT FRI OCT 22 2021  
 
THIS PERIOD WILL FOCUS ON:  
 
(1) THE HEAVY RAINFALL AND SEVERE STORM POTENTIAL ON SUNDAY  
(2) ADDITIONAL STRONG-TO-SEVERE POTENTIAL ON WEDNESDAY  
 
BY SATURDAY MORNING, GLOBAL MODELS ARE IN EXCELLENT AGREEMENT IN  
DEVELOPING A SURFACE LOW IN THE LEE OF THE ROCKIES WITH A BROAD  
WARM SECTOR DEVELOPING ACROSS THE SOUTHERN PLAINS. THE SURFACE LOW  
WILL BEGIN TO DEEPEN AND LIFT NORTHEASTWARD LATE SATURDAY NIGHT  
AS A ROBUST 500-MB SHORTWAVE TROUGH PUSHES ACROSS THE ROCKIES. BY  
SUNDAY MORNING, THE CENTER OF LOW PRESSURE WILL BE POSITIONED  
OVER NE KANSAS WITH A WARM FRONT EXTENDING EASTWARD INTO MISSOURI  
AND ILLINOIS ALONG THE I-70 CORRIDOR.  
 
ISENTROPIC ASCENT NORTH OF THE WARM FRONT WILL LEAD TO SHOWERS  
AND ELEVATED THUNDERSTORMS LATE SATURDAY NIGHT INTO SUNDAY MORNING  
FOR PORTIONS OF CENTRAL AND WEST CENTRAL ILLINOIS. RAINFALL RATES  
MAY BE HEAVY IN SPOTS, BUT THE HEAVIER RAINFALL RATES WILL COME  
LATER SUNDAY MORNING ONCE THE WARM FRONT LIFTS NORTHWARD ACROSS  
CENTRAL ILLINOIS. AS UNSEASONABLY HIGH PWATS IMPINGE ON THE  
SHARPENING WARM FRONT, THERE WILL LIKELY BE SOME FRONTOGENETIC  
FORCING INVOLVED TO HELP ENHANCE RAINFALL RATES TO 1.00" +/HR AT  
TIMES. THIS MAY LEAD TO SOME FLASH FLOODING, AS COLLABORATED AND  
MESSAGED BY WPC.  
 
THE SEVERE RISK APPEARS TO COME LATER IN THE EVENING ON SUNDAY AS  
A 40-50 KT LLJ VEERS INTO THE REGION AHEAD OF THE SURFACE COLD  
FRONT. PLENTY OF FORCING AND UPPER-LEVEL SUPPORT WILL BE PRESENT  
BY THAT TIME AS THE LEFT EXIT REGION OF THE UPPER-LEVEL SPEED MAX  
NOSES ACROSS THE MID-MISSISSIPPI VALLEY IN TANDEM WITH A STRONG  
500-MB SHORTWAVE TROUGH. ALL SEVERE WEATHER THREATS WILL BE  
POSSIBLE ACROSS CENTRAL ILLINOIS GIVEN THE HIGHLY SHEARED  
ENVIRONMENT JUXTAPOSED TO A MOIST AND MODESTLY UNSTABLE BOUNDARY  
LAYER. WITH THE TRIPLE POINT OF THE FRONTAL SYSTEM NEARBY,  
FORECAST HODOGRAPHS EXHIBIT SIGNIFICANT TURNING IN THE LOWEST FEW  
KILOMETERS, FURTHER SUPPORTING THE NOTION OF ORGANIZED SEVERE  
CONVECTION. THE SPC HAS COLLABORATED AND MESSAGED A SLIGHT RISK  
ACROSS MUCH OF THE FORECAST AREA SUNDAY EVENING.  
 
GUSTY WINDS AND SCATTERED SHOWERS WILL LINGER INTO MONDAY AS THE  
DYNAMIC STORM SYSTEM MAKES ITS DEPARTURE. LARGE SCALE SUBSIDENCE  
WILL BEGIN TO WORK IN BEHIND THE DEPARTING WAVE, AS AN AMPLIFIED  
RIDGE OF HIGH PRESSURE QUICKLY BUILDS ACROSS THE REGION ON  
TUESDAY.  
 
ANOTHER DYNAMIC STORM SYSTEM LOOKS TO LIFT ACROSS THE MISSISSIPPI  
VALLEY ON WEDNESDAY, WITH NOTABLE DIFFERENCES AMONG GLOBAL AND  
ENSEMBLE GUIDANCE. REGARDLESS OF THE TRACK OF THE SURFACE LOW,  
THERE WILL LIKELY BE ANOTHER GOOD SURGE OF GULF MOISTURE INTO  
SOUTHERN AND/OR CENTRAL ILLINOIS AHEAD OF THE COLD FRONT.  
INSTABILITY IS THE BIGGEST QUESTION AT THIS JUNCTURE, BUT THE  
SHEAR WILL BE THERE TO SUPPORT A FEW STRONG-TO-SEVERE STORMS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)  
ISSUED AT 1235 PM CDT FRI OCT 22 2021  
 
OBSERVATIONAL TRENDS AND SHORT-TERM GUIDANCE INDICATE THAT CLOUD  
BASES SHOULD GRADUALLY INCREASE THROUGHOUT THE AFTERNOON INTO THE  
EVENING. SUB-VFR CEILINGS MAY PERSIST AS LATE AS 00Z AT CMI AND  
OTHER LOCATIONS NEAR THE IN STATE LINE. OTHERWISE, AT LEAST SOME  
PERIODS OF VFR CIG/VSBY ARE EXPECTED FROM THIS AFTERNOON  
ESPECIALLY NEAR/WEST OF A LINE FROM KBMI-KDEC. VFR CONDITIONS ARE  
EXPECTED OVERNIGHT INTO SATURDAY MORNING EXCEPT PERHAPS FOR SOME  
MVFR/IFR VISIBILITY IN THE VICINITY OF KOLY/KAJG.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
UPDATE...AAT  
SYNOPSIS...AAT  
SHORT TERM...MJA  
LONG TERM...MJA  
AVIATION...AAT  
 
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