606  
FXUS63 KLOT 270147 AAC  
AFDLOT  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
847 PM CDT FRI MAY 26 2017  
   
UPDATE
 
 
847 PM CDT  
 
THE FINAL SHOWERS, ALONG WITH A COUPLE ELEVATED STORMS, SHOULD  
DEPART THE EASTERN CWA SHORTLY. ATTENTION FOR THE REST OF TONIGHT  
THEN TURNS TO FOG POTENTIAL. APART FROM THE PRESENT CLOUD COVER,  
IT'S A FAIRLY GOOD SETUP GIVEN EARLIER RAIN, LOW TEMPERATURE/DEW  
POINT SPREADS, AND LIGHT WINDS. GOES-16 SHORT WAVE INFRARED  
CHANNEL IS INDICATING SOME HOLES IN THE CLOUD COVER. DIFFICULT TO  
SAY HOW LONG ANY WILL PERSIST OR HOW THEY WILL EVOLVE, BUT IT MAY  
NOT TAKE ANY LENGTHY CLEARING FOR AT LEAST SHALLOW FOG TO DEVELOP.  
PATCHY FOG HAS BEEN ADDED TO THE FORECAST FOR MOST OUTLYING  
AREAS. WHILE CLIMATOLOGICALLY NOT FAVORED IN LATE MAY, CANNOT RULE  
OUT SOME POCKETS OF DENSE SHALLOW FOG, MAYBE MOST FAVORED IN THE  
SOUTHERN CWA.  
 
GIVEN THE AFOREMENTIONED UNCERTAINTY WITH CLOUD COVER, IT IS  
POSSIBLE THAT SATURDAY MORNING STARTS MOSTLY CLOUDY, OR WITH FOG,  
THAT SHOULD ERODE QUICKLY GIVEN THE SHALLOW NATURE OF THE LOW-  
LEVEL MOISTURE.  
 
MTF  
 

 
   
SHORT TERM
 
 
300 PM CDT  
 
TONIGHT THROUGH SATURDAY...  
 
FOR NEAR TERM CONVECTIVE/SEVERE THUNDERSTORM TRENDS, CHECK FOR THE  
LATEST MESOSCALE DISCUSSIONS ABOVE. THE WEATHER WILL QUIET DOWN  
TONIGHT WITH THE EFFECTIVE WARM FRONT SHUNTED WELL SOUTH BEHIND  
THE MCV. SHOWERS AND THUNDERSTORMS SHOULD EXIT QUICKLY BY THE  
EARLY TO MID EVENING HOURS. THIS WILL SET THE STAGE FOR A QUIET  
AND PLEASANT START TO THE MEMORIAL DAY WEEKEND, AT LEAST FOR THE  
DAYLIGHT PERIOD. STRONG HEATING WILL TAKE PLACE AWAY FROM LAKE  
INFLUENCE ON SATURDAY WITH PLENTY OF SUN FOLLOWED BY INCREASING  
MID AND HIGH CLOUDS DURING THE AFTERNOON. LOW LEVEL THERMAL PROGS  
SUPPORT HIGHS IN THE MID 70S TO AROUND 80 AWAY FROM THE LAKESHORE  
AND FEW MILES INLAND, WHICH WILL BE KEPT IN THE 60S.  
 
CASTRO  
 

 
   
LONG TERM
 
 
300 PM CDT  
 
SATURDAY NIGHT THROUGH FRIDAY...  
 
THE EFFECTIVE WARM FRONT WILL GRADUALLY LIFT NORTH IN ADVANCE OF A  
LIKELY ROBUST MCS, BUT MAINLY STAY CONFINED TO THE SOUTHERN CWA OR  
POINTS SOUTH. THERE IS UNCERTAINTY ON TIMING AND TRAJECTORY OF  
THIS MCS, WITH THE AN INCREASING LIKELIHOOD FOR MOST SIGNIFICANT  
IMPACTS TO REMAIN WELL SOUTH OF I-80 OR EVEN SOUTH OF THE CWA  
COUNTIES. PORTIONS OF THE AREA ARE LIKELY TO REMAIN FOR OUTDOOR  
ACTIVITIES DURING THE EVENING HOURS WITH LIKELY POPS FOR MOST  
WIDESPREAD SHOWER AND THUNDER COVERAGE AFTER MIDNIGHT (AND HIGHEST  
THUNDER COVERAGE ALONG/SOUTH OF I-80). DEEP LAYER SHEAR AND MUCAPE  
MAY BE SUFFICIENT TO SUPPORT AN ISOLATED HAIL THREAT AND PERHAPS  
LOCALIZED STRONG TO DAMAGING WINDS.  
 
A SURFACE LOW WILL TAKE SHAPE AND DRAG A COLD FRONT ACROSS THE  
AREA ON SUNDAY WITH PERHAPS AN ISOLATED RISK FOR GUSTY TO DAMAGING  
THUNDERSTORM WINDS AND MARGINALLY SEVERE HAIL SOUTHEAST OF I-55.  
THERE IS PLENTY OF UNCERTAINTY WITH THE CONVECTIVE SCENARIO ON  
SUNDAY AND MUCH OF THE AFTERNOON COULD CERTAINLY BE DRY NORTHWEST  
OF I-55 OR I-57. EXPECTING BREEZY WEST-NORTHWEST WINDS IN THE  
AFTERNOON BEHIND THE FRONT, WITH ONLY MODEST COOL ADVECTION SO  
HIGHS SHOULD REACH THE LOWER TO MID 70S.  
 
MEMORIAL DAY MONDAY COULD BE FAIRLY SIMILAR TO SUNDAY TEMPERATURE  
WISE. MAIN FEATURE OF NOTE IS A LARGE UPPER LOW OVER THE NORTHERN  
GREAT LAKES, FROM WHICH SOME ISOLATED DIURNALLY DRIVEN SHOWERS  
AND POSSIBLY THUNDERSTORMS COULD FORM DURING THE AFTERNOON. AGAIN,  
MOST OF THE DAY SHOULD BE DRY, SO NO NEED TO CANCEL OUTDOOR  
PLANS- JUST KEEP AN EYE ON THE FORECAST AND THE RADAR. THE UPPER  
LEVEL LOW PRESSURE WILL ONLY SLOWLY SLIDE EAST THROUGH THE WEEK,  
KEEPING AREA UNDER NORTHWEST FLOW ALOFT AND GENERALLY SLIGHTLY  
BELOW NORMAL TEMPERATURES FOR THE END OF MAY AND BEGINNING OF  
JUNE. CAN'T COMPLETELY RULE OUT ANY SHOWER ACTIVITY IN THE MID TO  
LATE WEEK, BUT IT LOOKS TO BE AN OVERALL DRIER REGIME.  
 
CASTRO  
 

 
   
AVIATION
 
 
FOR THE 00Z TAFS...  
 
701 PM...MAIN FORECAST CONCERNS ARE SCATTERED SHOWERS THIS  
EVENING AND CIGS THROUGH SATURDAY MORNING.  
 
SCATTERED SHOWERS WILL LIKELY CONTINUE ACROSS NORTHEAST IL  
THROUGH MID EVENING AND CONFIDENCE REGARDING HOW LONG THESE MAY  
PERSIST IS LOW. WEAK LOW PRESSURE WILL MOVE ACROSS THE REGION  
LATER TONIGHT AND MVFR CIGS ARE EXPECTED THIS EVENING AND THESE  
MAY PERSIST OVERNIGHT AND POSSIBLY LOWER INTO IFR BUT CONFIDENCE  
IS LOW AND TRENDS WILL NEED TO BE MONITORED THIS EVENING AND  
THROUGH THE NIGHT.  
 
EAST/NORTHEAST WINDS AROUND 10KT WILL SLOWLY DIMINISH LATER THIS  
EVENING AND POSSIBLY TURN MORE NORTHERLY OVERNIGHT...THOUGH SPEEDS  
WILL BE LIGHT. WINDS ARE EXPECTED TO TURN MORE EASTERLY SATURDAY  
MORNING AND INCREASE UP TO 10KTS SATURDAY AFTERNOON WITH A  
POSSIBLE LAKE BREEZE. CMS  
 

 
   
MARINE
 
 
227 PM CDT  
 
WILL KEEP THE MARINE FOG ADVISORY GOING AS WEB CAMS INDICATE  
HAZE/FOG REMAINS OVER THE OPEN WATERS.  
 
A HIGH PRESSURE RIDGE OVER THE LAKE WILL CONTINUE EAST. A WEAK  
SURFACE LOW OVER THE PLAINS WILL PASS SOUTH OF THE LAKE TONIGHT AND  
CONTINUE ACROSS THE OHIO VALLEY SATURDAY. THE LOW MAY CAUSE WIND  
SPEEDS TO INCREASE TO 10-20 KT OVER THE FAR SOUTHERN END OF THE LAKE  
THIS EVENING. ONE MODEL WOULD SUGGEST GUSTS UP TO 25 KT, BUT DO NOT  
HAVE ENOUGH CONFIDENCE TO GO THAT HIGH. HIGH PRESSURE PASSES OVER  
THE LAKE EARLY SATURDAY MORNING AND LIGHT WINDS WILL VARY IN  
DIRECTION ACROSS THE LAKE. VARIABLE WINDS ARE EXPECTED OVER THE  
SOUTHERN END AND SOUTHERLY WINDS OVER THE NORTHERN END.  
 
THE NEXT LOW FORMS OVER THE PLAINS SATURDAY AND REACHES THE GREAT  
LAKES REGION SUNDAY MORNING. THE LOW MOVES OVER MICHIGAN SUNDAY  
AFTERNOON AND WINDS BECOME WEST 10-20 KT BEHIND THE LOW. THE LOW  
OVER MICHIGAN MERGES WITH ANOTHER CANADIAN LOW TO THE NORTH OVER  
ONTARIO SUNDAY NIGHT. THE LOW IS FORECAST TO REMAIN RELATIVELY  
STATIONARY OVER ONTARIO EARLY NEXT WEEK WHICH MAY LEAD TO A AN  
EXTENDED PERIOD OF WESTERLY WINDS OF 15-25 KT. HIGH PRESSURE MOVES  
IN BEHIND THE LOW MID TO LATE NEXT WEEK.  
 
JEE  
 

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

 
 

 
 
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