507  
FXUS63 KLOT 182021  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
321 PM CDT THU JUL 18 2019  
   
SHORT TERM
 
 
313 PM CDT  
 
THROUGH SUNDAY...  
 
THE ONLY ADDITIONAL CHANGE MADE TO THE GOING HEADLINES WAS TO PUSH  
OFF THE START TIME OF LAKE AND PORTER IN UNTIL 15Z FRIDAY TO MATCH  
THE TIMING WE MADE EARLIER IN NORTHEAST IL.  
 
OVERALL, THE MORNING MCS PRODUCED A WAKE LOW WHICH SIGNIFICANTLY  
DISRUPTED THE LARGER SCALE SURFACE PRESSURE PATTERN OVER THE AREA.  
AS A RESULT, WE HAVE CONTINUED TO EXPERIENCE GUSTY EAST-  
SOUTHEASTERLY WINDS OVER MUCH OF NORTHEASTERN IL. THE REMNANT  
OUTFLOW BOUNDARY CURRENTLY RESIDES OVER FAR SOUTHERN BENTON AND  
IROQUOIS COUNTIES IN MY SOUTHEAST. TO THE NORTH OF THIS, WINDS  
ARE GENERALLY SOUTH-SOUTHEASTERLY. CLEARING SKIES HAS ALLOWED FOR  
SOME DECENT RECOVERY, WITH TEMPERATURES WARMING INTO THE LOWER TO  
MID 80S AT THE TIME OF THIS WRITING. IT STILL APPEARS THAT THIS  
TREND OF MODIFICATION WILL CONTINUE THROUGH LATE THIS AFTERNOON AS  
THE WINDS GRADUALLY VEER MORE SOUTH-SOUTHWESTERLY. BECAUSE OF  
THIS IT IS EXPECTED THAT OUR HIGH TEMPERATURES FOR THE DAY WILL  
HIT VERY LATE THIS AFTERNOON, OR EARLY THIS EVENING OVER NORTHERN  
IL.  
 
HEAT INDICES OVER FAR NORTHEASTERN IL AND NORTHWESTERN IN COULD  
CLIMB INTO THE 90S, TO POSSIBLY NEAR 100 IN A FEW AREAS BEFORE  
SUNSET AS TEMPERATURES RECOVER INTO THE MID TO UPPER 80S. HOWEVER,  
THE MORE EXTREME HEAT INDICES ARE LIKELY TO REMAIN SOUTH AND WEST  
OF THE CHICAGO AREA. FOR THIS REASON THE GOING START TIME OF 21Z  
SEEMS GOOD FOR AREAS OUTSIDE THE CHICAGO METRO AREA.  
 
THERE IS ANOTHER THREAT FOR SOME THUNDERSTORMS TONIGHT, BUT THIS  
THREAT WILL MAINLY RESIDE TO OUR NORTH IN WI AS THE LOW-LEVEL JET  
RAMPS UP AGAIN. THESE STORMS COULD AGAIN TREND TO THE EAST-  
SOUTHEAST, POSSIBLY REACHING FAR NORTHERN IL OVERNIGHT. IT DOES  
APPEAR THAT CAPPING WILL BE STRONGER TONIGHT OVER MUCH OF OUR  
AREA, SO IT APPEARS UNLIKELY THAT THESE STORMS WOULD SURVIVE TO  
FAR SOUTH INTO IL.  
 
OTHERWISE, THE HEAT WILL BE ON FOR THE ENTIRE AREA FOR BOTH FRIDAY  
AND SATURDAY. NOT MUCH HAS CHANGED WITH THE FORECAST FOR THESE TWO  
DAYS. OVERALL, WE ARE EXPECTING SIMILAR CONDITIONS EACH DAY, WITH  
HIGH TEMPERATURES IN THE MID TO POSSIBLY UPPER 90S, AND HEAT  
INDICES AROUND 110 TO POSSIBLY AS HIGH AS 115 IN SOME AREAS.  
OVERNIGHT LOWS BOTH TONIGHT AND FRIDAY NIGHT WILL REMAIN VERY WARM  
AND HUMID, SO LITTLE TO NO RELIEF IS EXPECTED AT NIGHT.  
 
A COLD FRONT IS EXPECTED TO DROP SOUTHWARD OVER NORTHERN IL LATER  
SATURDAY AFTERNOON AND EVENING. THIS FRONTAL PASSAGE WILL MARK  
THE END OF THE DANGEROUS HEAT ACROSS THE AREA, THOUGH IT WILL COME  
AT THE PRICE OF MORE STORMS. THUNDERSTORMS LOOK LIKE A GOOD BET  
OVER FAR NORTHERN IL AS EARLY AS LATE AFTERNOON SATURDAY, BUT  
MOST LIKELY OVER THE AREA SATURDAY NIGHT INTO SUNDAY EVENING.  
THESE STORMS ARE LIKELY TO BE VERY HEAVY RAIN PRODUCERS, AND SOME  
FLASH FLOOD RISK COULD DEVELOP AS THE EASTERLY STORM MOTION COULD  
RESULT IN TRAINING CELLS. THIS POSSIBILITY WILL NEED TO BE  
MONITORED. SOME OF THESE STORMS COULD ALSO BE ON THE STRONG SIDE,  
WITH STRONG WIND GUSTS.  
 
OTHERWISE, EXPECT MUCH COOLER CONDITIONS OVER THE AREA FOR SUNDAY  
WITH THE STORMS AND THE SHIFT TO NORTHERLY WINDS.  
 
KJB  
 

 
   
LONG TERM
 
 
320 PM CDT  
 
SUNDAY NIGHT THROUGH THURSDAY...  
 
A PERIOD OF MUCH QUIETER AND PLEASANT WEATHER IS EXPECTED FOR  
MUCH OF NEXT WEEK FOLLOWING THE SATURDAY NIGHT COLD FRONT PASSAGE.  
NORTHWEST FLOW ALOFT WILL SET UP OVER THE REGION FOR MUCH OF THE  
WEEK AS A LARGE UPPER RIDGE BUILDS IN THE WEST AND A TROUGH SETS  
UP OVER THE EAST. A LARGE AREA OF SURFACE HIGH PRESSURE IS LIKELY  
TO DROP SOUTHWARD OVER THE REGION EARLY NEXT WEEK AND THIS SHOULD  
RESULT IN MAINLY DRY AND COOL CONDITIONS OVER THE AREA.  
TEMPERATURES IN THIS PATTERN ARE LIKELY TO ONLY BE IN THE LOW TO  
MID 80S INLAND AND POSSIBLY INTO THE UPPER 70S ALONG THE LAKE  
SHORES. TEMPERATURES SHOULD BEGIN TO MODERATE BACK INTO THE MID TO  
UPPER 80S LATER IN THE WEEK.  
 
KJB  
 

 
   
AVIATION
 
 
FOR THE 18Z TAFS...  
 
LAST OF THE SHRA/TSRA ACTIVITY EXITING TO THE EAST AT THIS TIME.  
CEILINGS WILL QUICKLY IMPROVE OVER THE NEXT 1-2 HOURS AS WELL.  
SOUTHEAST WINDS TRAIL THE PRECIPITATION WITH SOME 20-25 KT GUSTS  
SHOWING UP IN THE CHICAGO METRO BUT THESE SHOULD BE SHORT LIVED.  
WINDS WILL TURN MORE SOUTH-SOUTHEAST AND EVENTUALLY SOUTH THROUGH  
MID TO LATE AFTERNOON. THERE MAY BE A LULL IN THE GUSTS PRIOR TO  
20Z BUT WITH INCREASING SUNSHINE DO EXPECT GUSTS INTO THE 20 TO  
PERHAPS 25 KT RANGE TO DEVELOP ACROSS THE TERMINALS. GUSTS WILL  
EASE THIS EVENING WITH A LIGHT SOUTH-SOUTHWEST BREEZE OVERNIGHT.  
GUSTS WILL INCREASE TO AROUND 20 KT LATER FRIDAY MORNING.  
 
ONE OTHER CONCERN IS FOR ANOTHER ROUND OF THUNDERSTORMS TO  
DEVELOP OVERNIGHT. AT THIS POINT, THEY ARE FAVORED TO REMAIN NORTH  
OF THE TERMINALS, BUT WILL INCLUDE A PROB30 FOR THUNDER AT RFD  
TOWARD DAYBREAK. WILL ALSO NEED TO WATCH FOR A WIND SHIFT TO  
SPREAD IN FROM THE NORTH IN CONJUNCTION WITH THE STORMS TO THE  
NORTH AND THEIR OUTFLOW BUT THIS IS A LOW PROBABILITY SCENARIO SO  
WILL NOT INCLUDE ANY MENTION IN THE TAFS.  
 
MDB  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...EXCESSIVE HEAT WARNING...ILZ008-ILZ010-ILZ011-ILZ019-ILZ020-  
ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 7 PM  
SATURDAY.  
 
EXCESSIVE HEAT WARNING...ILZ012-ILZ013-ILZ014...10 AM FRIDAY TO  
7 PM SATURDAY.  
 
HEAT ADVISORY...ILZ003 UNTIL 11 PM FRIDAY.  
 
HEAT ADVISORY...ILZ004-ILZ005-ILZ006...10 AM FRIDAY TO 11 PM  
FRIDAY.  
 
IN...EXCESSIVE HEAT WARNING...INZ001-INZ002...10 AM FRIDAY TO 7 PM  
SATURDAY.  
 
EXCESSIVE HEAT WARNING...INZ010-INZ011-INZ019 UNTIL 7 PM  
SATURDAY.  
 
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS  
UNTIL 7 PM THURSDAY.  
 

 
 

 
 
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