880  
FXUS63 KLOT 222354  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
654 PM CDT TUE JUN 22 2021  
   
SHORT TERM
 
 
317 PM CDT  
 
THROUGH WEDNESDAY NIGHT...  
 
IT WAS ANOTHER PLEASANT - COOLER THAN NORMAL - SUMMER DAY TODAY  
WITH HIGHS IN THE LOWER TO MID 70S WITH THE LOCAL AREA UNDER THE  
SURFACE RIDGE AXIS.  
 
OFF AND ON WARM ADVECTIVE SHOWERS ARE EXPECTED TO PUSH INTO THE  
AREA OVERNIGHT ALONG THE NOSE OF THE LOW-LEVEL JET, POTENTIALLY  
AIDED BY A WEAK MID-LEVEL DISTURBANCE. THESE SHOWERS ARE EXPECTED  
TO EXPAND IN COVERAGE OVERNIGHT INTO WEDNESDAY MORNING BUT SHOULD  
BE RATHER INTERMITTENT, RATHER THAN RAINING ALL NIGHT AND THROUGH  
THE MORNING. THERE IS A PERIOD WHERE GUIDANCE SHOWS A WEAK AXIS  
OF MUCAPE MOVES OVERHEAD WHICH WOULD SUPPORT AT LEAST MENTION OF  
EMBEDDED THUNDER POSSIBLE.  
 
THE UPPER TROUGH AXIS SHIFTS OFF TO THE EAST ON WEDNESDAY WITH  
WARMER AIR LIFTING BACK INTO THE AREA BEHIND THE SHOWERS. THIS  
WILL ALLOW TEMPERATURES TO WARM BACK INTO THE LOWER 80S FOR MOST  
AREAS. THIS WILL ALSO BE AIDED BY MIXING DOWN OF GUSTY WINDS  
THROUGH THE AFTERNOON WITH GUSTS UP TO 25-30 MPH POSSIBLE. THERE  
COULD BE A FEW ISOLATED SHOWERS THAT LINGER INTO THE AFTERNOON  
PERIOD, BUT FOR NOW WILL MAINTAIN A DRY FORECAST FOR THAT PERIOD.  
THE STRONG LOW LEVEL JET REMAINS OVERHEAD INTO WEDNESDAY NIGHT  
WHICH COULD ALLOW FOR SPORADIC STRONGER GUSTS TO PERSIST INTO THE  
EVENING AND OVERNIGHT HOURS.  
 
PETR  
 

 
   
LONG TERM
 
 
333 PM CDT  
 
THURSDAY THROUGH TUESDAY...  
 
MAIN LONG TERM FORECAST FOCUS CONTINUES TO BE ON THUNDERSTORM  
CHANCES AND COVERAGE THURSDAY INTO SATURDAY ALONG WITH THE POTENTIAL  
FOR LOCALLY HEAVY RAINFALL AND SEVERE WEATHER.  
 
AREAS OF CONVECTION ARE LIKELY WEST AND NORTHWEST OF THE CWA LATER  
WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING. GUIDANCE CONTINUES TO  
INDICATE A MINOR AMPLITUDE SHORT WAVE TROUGH WILL RIPPLE THROUGH  
WESTERLY MID-LEVEL FLOW, WHILE THE NOSE OF A SOUTHWESTERLY LOW LEVEL  
JET ORIENTS WARM/MOIST ADVECTION INTO FAR NORTHERN IL/SOUTHERN WI  
THURSDAY MORNING. THIS SUGGESTS AT LEAST SOME POTENTIAL FOR UPSTREAM  
CONVECTION TO WORK INTO ESPECIALLY NORTH CENTRAL IL AND THE IL/WI  
STATE LINE AFTER SUNRISE THURSDAY, THOUGH PERHAPS IN A DECAYING MODE  
BY THAT TIME. CONFIDENCE REMAINS FAIRLY LOW ON EVOLUTION INTO THE  
CWA, BUT CHANCE POPS CONTINUE TO APPEAR WARRANTED FOR THE NORTHWEST  
CWA THURSDAY. ITS POSSIBLE THAT PRECIP CHANCES WILL REMAIN  
ISOLATED/SCATTERED THURSDAY AFTERNOON/EVENING.  
 
MEDIUM-RANGE GUIDANCE IS IN REASONABLY GOOD AGREEMENT IN BRINGING  
ANOTHER SOMEWHAT MORE AMPLIFIED MID-LEVEL TROUGH ACROSS THE AREA  
LATE THURSDAY NIGHT INTO FRIDAY, BEFORE A LARGE UPPER TROUGH DIGS  
ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION INTO THE WEEKEND. A  
PAIR OF SURFACE LOWS ACCOMPANY THESE UPPER FEATURES, WHICH SLOWLY  
TRAIL A SURFACE COLD FRONT INTO THE AREA FRIDAY NIGHT THROUGH  
SUNDAY. SOME TIMING/LOCATIONS DIFFERENCES REMAIN, WHICH ALONG WITH  
ANY MODULATION OF MCS OUTFLOW BOUNDARIES AND EFFECTS ON INSTABILITY  
DURING THE THE PERIOD, BUT STRONG, POSSIBLY SEVERE THUNDERSTORMS ARE  
CERTAINLY POSSIBLE. IN ADDITION, PRECIPITABLE WATER VALUES APPROACH  
2 INCHES ON THURSDAY BUT ON FRIDAY WITH LOWER 70S DEWPOINTS,  
POSSIBLE MID 70S DEWPOINTS POOLING ALONG THE FRONTAL BOUNDARY,  
PRECIPITABLE WATER VALUES PUSH INTO THE 2 TO 2.30 INCH RANGE. THUS,  
TORRENTIAL RAIN AND LOCALIZED FLOODING WOULD BE POSSIBLE. MODEL QPF  
AMOUNTS VARY QUITE A BIT REGARDING THE PLACEMENT OF THE HEAVIEST  
AXIS, BUT IN GENERAL, THE MODELS ARE SHOWING THE POTENTIAL FOR  
SEVERAL INCHES OF RAIN NEARBY. HIGH POPS FROM THE BLENDED GUIDANCE  
STILL LOOK FINE FOR THIS TIME PERIOD.  
 
WITH THE UPPER TROUGH EXPECTED TO BE OVER THE REGION THROUGH AT  
LEAST EARLY NEXT WEEK, POSSIBLY CLOSING OFF AS AN UPPER LOW FOR A  
TIME AS THE ECMWF AND GEM ARE INDICATING, AT LEAST CHANCE POPS ARE  
NEEDED FOR THE REST OF THE EXTENDED PERIOD. ITS LIKELY THAT AS THESE  
TIME PERIODS APPROACH, POPS CAN BE TRIMMED AT NIGHT WITH MAINLY  
DIURNALLY DRIVEN ACTIVITY BUT TOO EARLY FOR THAT DETAIL YET. AND THE  
FRONT MAY BE STRONG ENOUGH TO CLEAR PRECIP FROM THE AREA FOR PART OF  
THE TIME THIS WEEKEND.  
 
BETTER MOISTURE AND FRONTAL FOCUS MOVES EAST/SOUTHEAST OF THE AREA  
INTO EARLY NEXT WEEK, THOUGH UPPER LOW WOBBLING IN THE VICINITY AS  
INDICATED IN EC/GEM SOLUTIONS MAY WARRANT AT LEAST SOME CHANCE  
POPS INTO MONDAY/TUESDAY.  
 
CMS/RATZER  
 
RATZER  
 

 
   
AVIATION
 
 
FOR THE 00Z TAFS...  
 
AVIATION FORECAST CONCERNS:  
 
* SHOWERS AND PERHAPS AN ISOLATED THUNDERSTORM OR TWO DEVELOPING  
LATE TONIGHT AND PERSISTING INTO WEDNESDAY MORNING.  
 
* SOUTH-SOUTHWEST WINDS BECOME SOMEWHAT GUSTY LATE TONIGHT AND  
MORE SO WEDNESDAY, WITH GUSTS NEAR 30 KTS POSSIBLE WEDNESDAY  
AFTERNOON.  
 
* BREEZY CONDITIONS PERSIST WEDNESDAY EVENING, MAINTAINING SOME  
DEGREE OF SURFACE GUSTS. 40-45 KT LOW LEVEL JET WILL RESULT IN  
LLWS POTENTIAL ESPECIALLY IF SURFACE GUSTS REMAIN ON THE LOWER  
SIDE.  
 
A MID-LEVEL DISTURBANCE DIGGING SOUTHEAST FROM THE UPPER MISSOURI  
VALLEY WAS INDUCING SOUTH-SOUTHWESTERLY RETURN FLOW WEST OF THE  
MISSISSIPPI RIVER LATE THIS AFTERNOON. THE RESULTING LOW LEVEL JET  
WAS PRODUCING ELEVATED SHOWERS AND THUNDERSTORMS WITHIN THE REGION  
OF MOIST ASCENT FOCUSED ACROSS IA EARLY THIS EVENING. THIS  
ACTIVITY IS EXPECTED TO DEVELOP EAST-SOUTHEAST INTO PARTS OF  
NORTHERN IL LATER THIS EVENING, WITH SHOWERS AND A FEW ISOLATED  
THUNDERSTORMS PERSISTING THROUGH WEDNESDAY MORNING AS THE LOW  
LEVEL AXIS SHIFTS EAST. THE BEST CHANCE OF THUNDERSTORMS IS EXPECTED  
TO REMAIN MAINLY TO THE WEST AND SOUTHWEST OF THE TERMINALS DURING  
THIS PERIOD, THOUGH AN ISOLATED THUNDERSTORM CAN'T BE RULED OUT  
ESPECIALLY EARLY WEDNESDAY MORNING. KRFD MAY HAVE THE BEST  
POTENTIAL FOR ISOLATED THUNDER, AND HAVE INCLUDED A TEMPO MENTION  
THERE LATER TONIGHT. IT DOES APPEAR THAT A PERIOD OF SCATTERED  
SHOWERS WILL AFFECT THE TERMINALS HOWEVER. CLOUD BASES AND  
PREVAILING VISIBILITIES ARE EXPECTED TO REMAIN VFR.  
 
LIGHT WINDS WILL BACK SOUTH-SOUTHWEST THIS EVENING, AND WILL  
INCREASE A BIT OVERNIGHT AS WARM ADVECTION STRENGTHENS. SOME GUSTS  
AROUND 20 KTS ARE POSSIBLE LATE DESPITE THE NOCTURNALLY STABILIZED  
BOUNDARY LAYER AS FLOW INCREASES ALOFT. SOUTHWEST WINDS WILL  
INCREASE WEDNESDAY, WITH GUSTS AROUND 30 KT POSSIBLE BY AFTERNOON  
AS THE SURFACE PRESSURE GRADIENT TIGHTENS AND 850 MB FLOW  
INCREASES INTO THE 30-35 KT RANGE. WINDS WILL LIKELY REMAIN  
SOMEWHAT GUSTY EVEN AFTER SUNSET WEDNESDAY NIGHT, THOUGH SOME  
POTENTIAL FOR LLWS WILL EXIST AS THE LOW LEVEL JET INCREASES TO  
40-45 KTS.  
 
RATZER  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...NONE.  

 
 

 
 
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