756  
FXUS63 KLOT 071954  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
254 PM CDT TUE JUL 7 2020  
   
SHORT TERM
 
 
248 PM CDT  
 
THROUGH WEDNESDAY NIGHT...  
 
A GENERALLY UNCAPPED ENVIRONMENT HAS BEEN COMMON ACROSS MUCH OF  
THE CWA EARLY THIS AFTERNOON, THOUGH SOURCES OF LIFT, LOW-LEVEL  
MIXING AND MID-LEVEL DRY AIR ENTRAINMENT HAVE LIMITED CUMULUS  
GROWTH FOR MOST AREA. A SUBTLE AND SMALL KINK IN THE MID-LEVELS  
EVIDENT IN WV IMAGERY WAS THE APPARENT EXTRA TRIGGER FOR STRONG  
CONVECTION OVER NORTHWEST INDIANA OVER THE PAST TWO HOURS. SINCE  
SURFACE MOISTURE WAS A LITTLE HIGHER (DEW POINTS AROUND 70F)  
COMPARED TO MOST OF THE ILLINOIS PORTION OF THE CWA (MID TO UPPER  
60S DEW POINTS), DEEPER VERTICAL GROWTH WAS ACHIEVED THERE.  
ADDITIONAL POCKETS OF TOWERING CUMULUS CONTINUE TO SHOW UP ON  
SATELLITE ACROSS THE REMAINDER OF THE CWA, MOST NOTABLY ON THE  
LAKE BREEZE IN COOK COUNTY. WITH A LACK OF DEEPER FORCING FOR THE  
NEXT COUPLE HOURS, DEVELOPMENT SHOULD BE SOMEWHAT LIMITED AWAY  
FROM THE LAKE BREEZE AND ANY REMNANT OUTFLOW BOUNDARIES FROM  
STORMS OVER THE PAST COUPLE HOURS.  
 
RAPID DEVELOPMENT OF CONVECTION AHEAD OF A PRONOUNCED MCV ACROSS  
NORTHEAST IOWA HAS OCCURRED IN THE PAST HOUR ACROSS SOUTHEAST MN  
AND SOUTHWEST WI. THIS ACTIVITY IS EXPECTED TO SLOWLY DRIFT EAST  
THROUGH THE REMAINDER OF THE AFTERNOON AMIDST WEAK DEEP-LAYER  
FLOW. WHILE SUBSTANTIAL COLD POOL DEVELOPMENT IS NOT EXPECTED,  
OUTFLOW FROM THIS ACTIVITY COMBINED WITH A TRAILING TROUGH INTO  
EASTERN IOWA WILL BECOME A RENEWED FOCUS FOR CONVECTION MOVING  
INTO THE CWA EARLY THIS EVENING. WITH MID-LEVEL LAPSE RATES  
BECOMING MORE UNFAVORABLE WITH EASTWARD EXTENT, OVERALL COVERAGE  
AND INTENSITY OF THE ACTIVITY SHOULD DIMINISH WITH TIME.  
ULTIMATELY, RESIDUAL THUNDERSTORMS MAY REACH NORTH-CENTRAL IL  
PRIOR TO SUNSET, WITH POSSIBLY SOME REMNANT SHOWERS SURVIVING INTO  
THE CHICAGO METRO CLOSE TO MIDNIGHT.  
 
A MID-LEVEL RIDGE AXIS DRIFTING OVER THE CWA WEDNESDAY MORNING  
WILL SHIFT FAR ENOUGH EAST BY THE AFTERNOON TO ALLOW CAPPING FROM  
THE SUBSIDENCE INVERSION TO WEAKEN. WHILE SLIGHT CAPPING SHOULD  
REMAIN, ISOLATED CONVECTION COULD DEVELOP WHERE FOCUSED  
CONVERGENCE EXISTS. PRIMARILY THIS WOULD BE ALONG THE LAKE  
MICHIGAN LAKE BREEZE AND ANY POTENTIAL REMNANT OUTFLOW BOUNDARIES  
FROM CONVECTION THIS EVENING.  
 
LITTLE CHANGE WAS MADE TO THE TEMPERATURE FORECAST FOR WEDNESDAY  
AS THE WARM STRETCH CONTINUES. WITH WEAKER CAPPING IN PLACE,  
DAYTIME MIXING SHOULD AT LEAST LOWER AFTERNOON DEW POINTS A COUPLE  
DEGREES FROM THE MORNING HOURS AS HAS BEEN THE CASE FOR SEVERAL  
DAYS NOW. MAX TEMPS IN THE 92-94 RANGE INLAND COMBINED WITH  
AFTERNOON DEW POINTS IN THE UPPER 60S WILL PRODUCE HEAT INDEX  
VALUES IN THE 95- 100F RANGE.  
 
KLUBER  
 

 
   
LONG TERM
 
 
254 PM CDT  
 
THURSDAY THROUGH TUESDAY...  
 
THURSDAY WILL BE SIMILAR TO WEDNESDAY WITH HOT AND HUMID CONDITIONS  
REMAINING, WITH HIGH TEMPS PERHAPS A SMIDGE LOWER THAN BEFORE DUE TO  
INCREASING CLOUD COVER. THURSDAY EVENING INTO FRIDAY, SHOWER AND  
THUNDERSTORM CHANCES WILL INCREASE AS AN UPPER-LEVEL WAVE AND  
PERHAPS A CONVECTIVELY-GENERATED MCV APPROACHES FROM THE WEST.  
DEPENDING ON THE TIMING OF THE WAVE, A FEW "PULSEY" STRONG TO SEVERE  
STORMS LOOK POSSIBLE WITH FREQUENT LIGHTNING, TORRENTIAL DOWNPOURS,  
SMALL HAIL, AND WIND GUSTS STRONG ENOUGH TO DOWN TREE LIMBS AS THE  
MAIN RISKS.  
 
THIS WEEKEND, THE GREAT LAKES WILL BE POSITIONED BENEATH WEAK UPPER-  
LEVEL TROUGHING LEADING TO A BREAK IN THE HOT AND HUMID  
CONDITIONS. SUNDAY APPEARS TO BE THE COOLEST DAY WITH HIGHS  
TOPPING OFF IN THE MID TO UPPER 80S AS A SECONDARY COLD FRONT  
SNEAKS IN FROM THE NORTH. HAZARDOUS SWIMMING CONDITIONS MAY  
DEVELOP IN THE WAKE OF THE FRONT FOR LAKE MICHIGAN BEACHES SUNDAY  
AFTERNOON AND EVENING.  
 
BORCHARDT  
 

 
   
AVIATION
 
 
FOR THE 18Z TAFS...  
 
DEEP CONVECTION IS ATTEMPTING TO DEVELOP ON VARIOUS SURFACE  
BOUNDARIES ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA AT TAF  
ISSUANCE, PRIMARILY ON A LAKE BREEZE IN NORTHWEST INDIANA AND A  
WEAK SURFACE TROUGH FROM NORTH-CENTRAL TO WEST-CENTRAL ILLINOIS.  
ISOLATED TO WIDELY SCATTERED ACTIVITY IS EXPECTED TO CONTINUE TO  
DEVELOP THROUGH THE AFTERNOON ON THESE FEATURES. CONFIDENCE IN TS  
DIRECTLY AFFECTING A GIVEN TERMINAL REMAINS LOW ENOUGH TO PRECLUDE  
A TEMPO TS GROUP IN THE TAF, BUT COVERAGE SHOULD BE HIGH ENOUGH  
THAT AIRSPACES AROUND THE TERMINALS MINIMALLY SEE SOME IMPACTS.  
WHILE MID-LEVEL DRY AIR ENTRAINMENT WILL LIMIT INTENSITY OF MOST  
CELLS, A FEW COULD BECOME DEEP ENOUGH TO PRODUCE GUSTY DOWNDRAFTS  
OF 20-30 KNOTS IMMEDIATELY UNDER AND NEAR THE CELL.  
 
A LOW TO MID-LEVEL WAVE MOVING SOUTHEAST ACROSS SOUTHEAST MN AND  
NORTH-CENTRAL IA IS EXPECTED TO FORCE SCATTERED CONVECTION THROUGH  
THIS AFTERNOON. IF COVERAGE BECOME HIGH ENOUGH TO FORM LARGER  
CLUSTERS OF STORMS OR ANY EXISTING STORMS ARE MAINTAINED INTO THE  
EVENING, RESIDUAL SHOWERS AND OUTFLOW WINDS MAY AFFECT THE  
CHICAGO- AREA TERMINALS MID TO LATE EVENING.  
 
OTHERWISE, CONDITIONS SHOULD BE RELATIVELY QUIET THROUGH THE  
MORNING HOURS ON WEDNESDAY, WITH VRB WINDS 5 KNOTS OR LESS  
(FAVORING THE SE QUADRANT THIS EVENING AND SW QUADRANT OVERNIGHT  
INTO WEDNESDAY MORNING.) ENOUGH CAPPING SHOULD EXIST FOR ORD/MDW  
ON WEDNESDAY AFTERNOON TO LIMIT CONVECTIVE POTENTIAL ON A LAKE  
BREEZE, BUT A WIDELY ISOLATED THUNDERSTORM CANNOT BE RULED OUT.  
 
KLUBER  
 

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

 
 

 
 
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