524  
FXUS63 KLOT 211134  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
634 AM CDT SUN OCT 21 2018  
   
SHORT TERM
 
 
212 AM CDT  
 
TODAY AND TONIGHT...  
 
QUIET WEATHER RETURNS TO THE REGION TODAY, IN THE WAKE OF  
SATURDAY'S GUSTY COLD FRONT. TEMPERATURES WILL REMAIN BELOW  
NORMAL, DESPITE PLENTIFUL SUNSHINE.  
 
SURFACE HIGH PRESSURE CENTERED OVER THE MID-MISSISSIPPI VALLEY  
EARLY THIS MORNING WILL SPREAD SOUTHEAST ACROSS THE OHIO AND  
TENNESSEE RIVER VALLEYS BY EVENING. LIGHT WINDS WILL BACK  
SOUTHWEST AS THE RIDGE MOVES AWAY FROM THE REGION, WITH A MODEST  
INCREASE IN SPEEDS AS THE GRADIENT TIGHTENS. IT WILL BECOME MORE  
BREEZY DURING THE AFTERNOON, ESPECIALLY ACROSS THE NORTHWEST HALF  
OF THE CWA, AS GUSTS DEVELOP AND INCREASE TO AROUND 20 MPH BEFORE  
DIMINISHING WITH SUNSET. OTHER THAN A LITTLE CIRRUS CLIPPING THE  
AREA IN ASSOCIATION WITH AN UPPER LEVEL JET STREAK TO OUR NORTH,  
SKIES WILL BE SUNNY TODAY. THIS, COMBINED WITH A DEEPENING OF THE  
MIXED LAYER, SHOULD SUPPORT TEMPS REBOUNDING TO NEAR THE 50 DEGREE  
MARK IN MANY AREAS, THOUGH THE DEEPEST MIXING LOOKS TO COME LATE  
IN THE DAY.  
 
AN AREA OF LOW PRESSURE WILL TRACK FROM THE CANADIAN PRAIRIES TO  
NORTH OF THE GREAT LAKES TONIGHT AND MONDAY, AND WILL TRAIL A COLD  
FRONT ACROSS THE UPPER MIDWEST OVERNIGHT. SURFACE WINDS WILL  
REMAIN SOUTHWESTERLY IN ADVANCE OF THE FRONT TONIGHT, HELPING TO  
KEEP TEMPS UP IN THE LOW-MID 30S TONIGHT.  
 
RATZER  
 

 
   
LONG TERM
 
 
212 AM CDT  
 
MONDAY THROUGH SATURDAY...  
 
DRY WEATHER WILL PERSIST THROUGH MID-WEEK, WHILE TEMPERATURES  
CONTINUE TO AVERAGE COOLER THAN NORMAL THROUGH MOST OF THE PERIOD.  
PRECIPITATION LOOKS TO BE NON-EXISTENT UNTIL FRIDAY/SATURDAY.  
 
FAIRLY STRONG SHORT WAVE AND ITS ASSOCIATED SURFACE LOW PROPAGATE  
THROUGH NORTHWEST FLOW ACROSS ONTARIO AND THE GREAT LAKES REGION  
MONDAY, TRAILING A COLD FRONT ACROSS THE FORECAST AREA DURING THE  
DAY. DRY LOW AND MID LEVELS AS INDICATED BY NAM/GFS SOUNDINGS  
INDICATE A DRY COLD FROPA, AND ONLY A PERIOD OF PATCHY HIGH CLOUDS  
ARE EXPECTED. SOUTHWEST WINDS AHEAD OF THE FRONT IN THE WARM  
SECTOR WILL SUPPORT A MODEST WARM-UP, DEPICTED BY PROGGED 925 MB  
TEMPERATURES OF +7/+8 C SUPPORTIVE OF UPPER 50S/LOWER 60S SURFACE  
TEMPS. COLD FRONT SETTLES ACROSS THE SOUTH/SOUTHEAST COUNTIES OF  
THE FORECAST AREA MONDAY EVENING.  
 
SURFACE HIGH PRESSURE EXPANDS SOUTHEASTWARD FROM CENTRAL CANADA  
AND THE NORTHERN PLAINS ON TUESDAY, AS THE LARGER SCALE UPPER  
TROUGH OVER THE EASTERN CONUS SHIFTS EASTWARD. UPPER RIDGING  
DEVELOPS ALOFT, ALLOWING THE SURFACE HIGH TO LINGER ACROSS THE  
AREA THROUGH THE MID-WEEK PERIOD, BEFORE EVENTUALLY DRIFTING OFF  
TO THE EAST BY THURSDAY. DRY AND COOLER THAN AVERAGE WEATHER, BUT  
WITH GENERALLY CLEAR SKIES, WILL BE THE RULE TUESDAY AND  
WEDNESDAY.  
 
EVENTUALLY, THE CUT-OFF LOW CURRENTLY ALONG THE SOUTHERN  
CALIFORNIA COAST IS PROGGED TO LIFT SLOWLY OUT ACROSS THE PLAINS  
AND INTO THE MIDWEST TOWARD THE REGION LATE IN THE WEEK. MODEL  
PRECIP OUTPUT IS HIT AND MISS INITIALLY AS THE APPROACHING WAVE  
WORKS AGAINST DEEP DRY AIR MASS ACROSS THE MIDWEST, WITH THE GULF  
BLOCKED BY SPRAWLING SURFACE HIGH PRESSURE. LIGHT RAIN POTENTIAL  
DOES LOOK TO EVENTUALLY INCREASE BY THE END OF THE PERIOD HOWEVER,  
AS THE HIGH MOVES OFF TO THE EAST AND SOME DEGREE OF LOW LEVEL  
MOISTURE RETURN DEVELOPS INTO THE LOWER-MIDDLE MISSISSIPPI VALLEY.  
 
RATZER  
 

 
   
AVIATION
 
 
FOR THE 12Z TAFS...  
 
634 AM...ONLY FORECAST CONCERN THIS PERIOD REMAINS THE WINDS.  
LIGHT WESTERLY WINDS WILL TURN SOUTHWESTERLY THIS MORNING AND  
INCREASE IN SPEEDS TO 10-15KTS BY EARLY AFTERNOON. SOME GUSTS TO  
20KTS WILL BE POSSIBLE THIS AFTERNOON INTO SUNSET. THERE REMAINS  
UNCERTAINTY REGARDING HOW STRONG THE LOW LEVEL WINDS WILL BECOME  
THIS EVENING AND WHETHER LOW LEVEL WIND SHEAR WILL MATERIALIZE BUT  
MAINTAINED MENTION WITH THIS FORECAST. THESE LOW LEVEL WINDS DO  
APPEAR TO DIMINISH TOWARD SUNRISE MONDAY MORNING. CMS  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...SMALL CRAFT ADVISORY...WINTHROP HARBOR TO GARY IN UNTIL 10 AM  
SUNDAY.  
 
SMALL CRAFT ADVISORY...GARY TO MICHIGAN CITY IN UNTIL 1 PM SUNDAY.  
 

 
 

 
 
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