257  
FXUS63 KLOT 242332  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
632 PM CDT THU SEP 24 2020  
   
SHORT TERM
 
 
155 PM CDT  
 
THROUGH FRIDAY NIGHT...  
 
AN UPPER LEVEL TROUGH ACROSS NE IA INTO SOUTHERN WI WILL CONTINUE TO  
DAMPEN AS IT MOVES ACROSS NORTHERN IL AND NORTHWEST IN THIS EVENING  
AND OVERNIGHT. A NARROW BAND OF SPRINKLES/BRIEF SHOWERS EXTENDS  
SOUTH FROM WI INTO IL AND COULD GRAZE AREAS ALONG AND WEST OF  
I-39. OTHERWISE, WITH THIS FEATURE WEAKENING EXPECT MAINLY AN  
INCREASE IN CLOUDS.  
 
OUR MILD WEATHER WILL CONTINUE INTO FRIDAY WITH BREEZY SOUTH-  
SOUTHWESTERLY WINDS AND MOSTLY CLEAR SKIES (WITH THE EXCEPTION OF  
THE PERSISTING ELEVATED WILDFIRE SMOKE) EXPECTED. HIGH  
TEMPERATURES WILL BE SLIGHTLY WARMER THAN THURSDAY'S HIGHS THANKS  
TO LOW LEVEL WARM ADVECTION IN SOUTHWESTERLY WINDS UNDER THE  
STRENGTHENING UPPER RIDGE. WITH READINGS IN THE MID TO UPPER 70S  
TODAY, EXPECT HIGHS AROUND 80 OR SO IN MOST LOCATIONS. THE UPPER  
JET WILL REMAIN FOCUSED TO OUR NORTH FRIDAY NIGHT KEEPING MILD  
CONDITIONS IN PLACE THROUGH THE NIGHT AND SETTING THE STAGE FOR A  
WARM SATURDAY.  
 
KMD  
 

 
   
LONG TERM
 
 
241 PM CDT  
 
SATURDAY THROUGH THURSDAY...  
 
THE PERIOD STARTS WITH A SUMMER-LIKE, BUT BREEZY, FEEL ON  
SATURDAY, BUT A ROBUST PATTERN CHANGE IS EXPECTED INTO NEXT WEEK,  
AND THIS WILL CERTAINLY MAKE FOR MORE OCTOBER-LIKE WEATHER ACROSS  
THE AREA.  
 
ON SATURDAY AN UPPER LEVEL IMPULSE IS EXPECTED TO SHIFT EASTWARD  
ACROSS THE DAKOTAS AS THE EXIT REGION OF AN UPPER LEVEL JET NOSES  
INTO THE UPPER MIDWEST. THE LOWER-LEVEL MASS RESPONSE TO THIS WILL  
RESULT IN STRENGTHENING SOUTH-SOUTHWESTERLY FLOW ACROSS THE  
MIDWEST AND INTO THE GREAT LAKES DURING THE DAY. THIS WILL IN  
RETURN SET UP SOME STRONG WARM AIR ADVECTION ACROSS THE AREA, WITH  
A THERMAL RIDGE FEATURING 850 (925) MB TEMPERATURES IN THE LOW  
(MID) 20S CELCIUS SHIFTING OVERHEAD SATURDAY AFTERNOON. THIS AIR  
MASS SHOULD BE WARM ENOUGH TO SUPPORT MID TO POSSIBLY EVEN SOME  
UPPER 80 DEGREE HIGH TEMPERATURES SATURDAY AFTERNOON. SURFACE  
WINDS ALSO LOOK TO BE GUSTY UP TO AROUND 35 MPH OUT OF THE  
SOUTHWEST.  
 
A SURFACE COLD FRONT IS EXPECTED TO SHIFT INTO NORTHERN IL ON  
SUNDAY MORNING, BEFORE SETTLING OVER CENTRAL IL AND IN IN THE  
AFTERNOON. TEMPERATURES IN THE WAKE OF THE FRONT WILL BE COOLER,  
ESPECIALLY OVER FAR NORTHERN IL WHERE READINGS WILL LIKELY BE IN  
THE LOWER TO MIDDLE 70S. AT THIS TIME THE FRONT LOOKS TO MOVE  
THROUGH PRECIPITATION FREE DURING THE MORNING SUNDAY. HOWEVER, IT  
APPEARS OUR CHANCES FOR SOME RAIN SHOWERS WILL INCREASE A BIT  
LATER SUNDAY INTO SUNDAY EVENING AS A ROBUST UPPER TROUGH DIGS  
OVER THE AREA AND INTERACTS WITH THE LOWER-LEVEL BAROCLINIC ZONE  
OVERHEAD. THESE SHOWERS MAY CONTINUE INTO MONDAY AS WELL AS  
ANOTHER SURFACE LOW TRIES TO DEVELOP JUST TO OUR SOUTHEAST IN THE  
VICINITY OF THE SURFACE BOUNDARY. CONFIDENCE IS A BIT LOW,  
HOWEVER, WITH THE EXTENT OF RAIN SHOWERS OVER OUR AREA ON MONDAY,  
AS THERE ARE SOME QUESTIONS AS TO HOW THIS POTENTIAL SURFACE LOW  
MAY EVOLVE. ONE THING THAT IS OF HIGHER CONFIDENCE IS THE MUCH  
COOLER CONDITIONS ON MONDAY, WITH HIGHS IN THE 60S AREAWIDE.  
 
FOLLOWING MONDAY IT APPEARS THAT THE AREA COULD BE IN FOR A PERIOD  
OF EVEN COOLER WEATHER FOR THE MIDDLE TO END OF THE WEEK. THIS AS  
THE LARGE SCALE UPPER-LEVEL PATTERN BECOMES AMPLIFIED ACROSS  
NORTH AMERICA. THIS PATTERN LOOKS TO FEATURE A MEAN TROUGH OVER  
MUCH OF THE UPPER MIDWEST AND GREAT LAKES REGIONS AND A DOMINATE  
UPPER RIDGE OVER WESTERN NORTH AMERICA. IN ADDITION TO THE MUCH  
BELOW NORMAL TEMPERATURES NEXT WEEK, WE COULD ALSO EXPERIENCE SOME  
PERIODS OF SHOWERS ASSOCIATED WITH SMALLER SCALE DISTURBANCES  
SHIFTING OVERHEAD IN THE CYCLONIC FLOW ALOFT. THE DETAILS OF THESE  
DISTURBANCES AND ANY ASSOCIATED RAIN ARE UNCLEAR AT THIS TIME.  
FOR THIS REASON, I DID NOT STRAY FROM THE NATIONAL BLEND GUIDANCE,  
WHICH GIVES LOWER CHANCE POPS THROUGH MUCH OF THE PERIOD.  
 
KJB  
 

 
   
AVIATION
 
 
FOR THE 00Z TAFS...  
 
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. MID TO HIGH  
LEVEL CLOUDS WILL LINGER THROUGH THE EVENING HOURS BEFORE  
GRADUALLY CLEARING OUT OVERNIGHT. SOUTH TO SOUTHWESTERLY WINDS  
WILL CONTINUE OVERNIGHT AND THROUGH THE DAY TOMORROW, WITH  
OCCASIONAL GUSTS TO 18 TO 20 KT POSSIBLE BY LATE MORNING.  
 
PETR  
 

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

 
 

 
 
VISIT US AT WEATHER.GOV/CHICAGO  
 
FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:  
WWW.FACEBOOK.COM/NWSCHICAGO  
WWW.TWITTER.COM/NWSCHICAGO  
WWW.YOUTUBE.COM/NWSCHICAGO  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab IL Page
The Nexlab IN Page Main Text Page