033  
FXUS63 KLOT 181127  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
627 AM CDT WED SEP 18 2019  
   
SHORT TERM
 
 
203 AM CDT  
 
THROUGH THURSDAY...  
 
DRIER AIR JUST OFF THE SURFACE HAS LIMITED MUCH OTHER THAN SOME  
PATCHY FOG EARLY THIS MORNING, AND WE'VE NOTED EVEN AHEAD OF THE  
CIRRUS SOME DEWPOINT LOWERING WITH THE LIMITED TEMPERATURE FALLS.  
NIGHTIME MICROPHYSICS SATELLITE IS PICKING UP A SLIGHTLY MORE  
FOCUSED AREA OF FOG IN WI THAT EXTENDS INTO MCHENRY COUNTY,IL, SO  
SOME BRIEF EXPANSION IS POSSIBLE.  
 
THE UPPER RIDGE IS STILL IN PLACE OVERHEAD AS A STRONGER UPPER LOW  
SPINS ACROSS THE NORTHERN PLAINS. SEVERAL WAVES ARE NOTED IN THE  
SOUTHWEST FLOW, THE ONES CLOSER TO OUR REGION ONLY RESULTING IN  
SOME CIRRUS, WITH A STRONGER WAVE AND MOISTURE TRANSPORT AXIS  
DRIVING WHAT SHOULD BE INCREASED THUNDERSTORM ACTIVITY ACROSS THE  
UPPER MIDWEST. EXPECT SOME WEAKENING OF THIS OVERNIGHT ACTIVITY  
BEFORE STORMS ACROSS THIS CORRIDOR REFORM AHEAD OF AN ADVANCING  
COLD FRONT. LOCALLY THIS WILL SLOWLY PUSH THE SURFACE HIGH  
RESPONSIBLE FOR OUR PLEASANT WEATHER THE LAST FEW DAYS TO  
EASTWARD. BUT FOR TODAY, EXPECT OCCASIONAL PASSING CIRRUS,  
ESPECIALLY THIS MORNING. WE WILL STILL FEEL THE INFLUENCE OF THE  
HIGH WITH DRY SOUTHEAST WINDS. INCREASING 925 MB TEMPS SHOULD  
SUPPORT EVEN FURTHER WARMING TODAY, WITH 80S AGAIN COMMON INLAND,  
AND MID 70S AT THE LAKE. COULD EVEN HAVE A LITTLE LAKE BREEZE.  
 
THE MAIN MOISTURE AXIS WILL PUSH CLOSE TO THE MISSISSIPI VALLEY  
OVERNIGHT. MODEL GUIDANCE FOR DAYS HAS SUGGESTED THE DEVELOPMENT  
OF ANOTHER COMPLEX OF THUNDERSTORMS AS THE LOW LEVEL JET INCREASES  
OVERNIGHT. DRY AIR AND SOME LINGERING SURFACE HIGH INFLUENCE  
SHOULD LARGELY KEEP THIS ACTIVITY OFF TO OUR WEST TONIGHT. IN  
SPITE OF THE INITIAL HIGHER CLOUD COVER, THURSDAY SHOULD BE  
EQUALLY WARM IF NOT WARMER, AND COULD PUSH 80 EVEN AT THE LAKE  
BEFORE ANY LAKE BREEZE INFLUENCE DEVELOPS. LOW TO MID 80S WILL  
RULE INLAND AREAS, WARMEST SOUTHERN LOCALES.  
 
KMD  
 

 
   
LONG TERM
 
 
314 AM CDT  
 
THURSDAY NIGHT THROUGH TUESDAY...  
 
THURSDAY NIGHT AND FRIDAY: A RATHER PRONOUNCED MID-LEVEL RIDGE WILL  
REMAIN ENTRENCHED ACROSS THE GREAT LAKES REGION DURING THIS PERIOD,  
WITH CONTINUED UNSEASONABLY WARM CONDITIONS INTO FRIDAY, WHEN TEMPS  
IN THE MID TO POTENTIALLY UPPER 80S RUN 10F+ ABOVE NORMAL.  
 
WEAK DISTURBANCES WILL CONTINUE TO ROUND THE WESTERN EXTENT OF THIS  
RIDGE OVER A MODERATELY UNSTABLE AIR MASS. CONVECTION OVER IOWA ON  
THURSDAY AFTERNOON MAY SNEAK INTO THE NW CWA IN A DECAYING MODE AS  
IT OUTRUNS MUCH BETTER INSTABILITY AND INTO A MORE CAPPED  
ENVIRONMENT. DEPENDING ON HOW FAR EAST THIS CONVECTION REACHES, A FEW  
STORMS MAY DEVELOP ON A RESULTANT OUTFLOW BOUNDARY OVER THE NW CWA  
FRIDAY AS CAPPING WEAKENS FROM MINOR COOLING IN THE 925-850 HPA  
LAYER. OVERALL, DRY WEATHER FOR MUCH OF THE AREA FOR A SIGNIFICANT  
PORTION OF THIS TIME PERIOD CAN BE EXPECTED.  
 
SATURDAY THROUGH SUNDAY: DEEP TROUGHING CURRENTLY OVER THE PACIFIC  
NORTHWEST WILL QUICKLY ERODE THE RIDGE ACROSS THE GREAT LAKES THIS  
WEEKEND. A COLD FRONT WELL REMOVED FROM ITS PARENT LOW OVER HUDSON  
BAY WILL THEN APPROACH THE AREA ON SATURDAY, SLOWLY CROSSING THE CWA  
ON SUNDAY. THIS OCCURS AS ABUNDANT MOISTURE ASSOCIATED NOW TROPICAL  
DEPRESSION IMELDA IS ADVECTED INTO THE REGION AHEAD OF THE FRONT.  
PWAT VALUES OF AROUND 1.8" WILL BE NEAR THE CLIMATOLOGICAL MAX FOR  
THE THIRD WEEK OF SEPTEMBER. PUTTING ALL THIS TOGETHER, MULTIPLE  
ROUNDS OF HEAVY SHOWERS AND/OR THUNDERSTORMS WILL BE POSSIBLE  
SATURDAY NIGHT THROUGH SUNDAY, THOUGH ISOLATED TO SCATTERED ACTIVITY  
MAY PRECEDE THE FRONT ON SATURDAY. WILL CONTINUE TO MONITOR THIS  
PERIOD FOR A RENEWED FLOODING RISK.  
 
BY EARLY NEXT WEEK, GUIDANCE DIVERGES WITH THE HANDLING OF A WESTERN  
CONUS TROUGH, THOUGH IT LOOKS AS IF IT WILL BECOME CUTOFF BEFORE  
REACHING THE GREAT PLAINS. MODEST MID-LEVEL RIDGING WOULD THEN BE  
THE DOMINATE FEATURE ACROSS THE AREA, PRODUCING GENERALLY QUIET  
CONDITIONS.  
 
KLUBER  
 

 
   
AVIATION
 
 
FOR THE 12Z TAFS...  
 
VFR CONDITIONS WITH PASSING UPPER-LEVEL CLOUDS ARE EXPECTED  
THROUGHOUT THE PERIOD. WIND DIRECTION WILL LIKELY SETTLE AROUND 170  
THROUGH AT LEAST MID AFTERNOON AT ORD/MDW. HOWEVER, SOME TEMPORARY  
VEERING TO 190 OR POSSIBLY 200 AT AROUND 10 KNOTS IS EXPECTED MID  
MORNING INTO EARLY AFTERNOON AS STRONGER SSW WINDS AT 1-2 KFT ARE  
MIXED DOWN TO THE SURFACE. A LAKE-INDUCED BACKING OF THE WINDS TO  
SE/ESE SHOULD THEN OCCUR MID TO LATE AFTERNOON AT ORD/MDW.  
 
KLUBER  
 

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

 
 

 
 
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