277  
FXUS63 KLOT 270818  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
318 AM CDT MON MAR 27 2017  
   
SHORT TERM
 
 
243 AM CDT  
 
THROUGH TONIGHT...  
 
EARLY THIS MORNING, FOGGY CONDITIONS ARE IN PLACE AS A WEAK  
SURFACE TROUGH MOVES ACROSS THE AREA RESULTING IN WEAK FLOW. TO  
OUR SOUTHWEST, WATER VAPOR IMAGERY SHOWS AN UPPER LOW SPINNING  
OVER EASTERN KS WHILE A SURFACE LOW IS ANALYZED OVER FAR  
SOUTHEASTERN KS. AS THE LOW MOVES EAST ACROSS MISSOURI TODAY, A  
COL AREA WILL MOVE OVER NORTHERN ILLINOIS AND NORTHWEST INDIANA  
RESULTING IN LIGHT AND VARIABLE OR CALM WINDS THROUGH MUCH OF THE  
MORNING OVER THE CWA WHICH WILL DELAY OR SLOW IMPROVEMENT OF  
VISIBILITY POSSIBLY INTO THE AFTERNOON FOR SOME AREAS. THIS  
AFTERNOON, SURFACE LOW IS PROGGED TO MOVE EAST ACROSS THE MID  
MISSISSIPPI VALLEY INTO FAR DOWNSTATE ILLINOIS WITH A  
NORTHEASTERLY GRADIENT DEVELOPING OVER NORTHERN ILLINOIS. ONSHORE  
FLOW AND FOG OVER LAKE MICHIGAN WILL SUPPRESS TEMPERATURES NEAR  
THE LAKE FRONT. EXPECT HIGH TEMPERATURES IN THE MID TO UPPER 50S  
WITH A FEW SPOTS SOUTH OF I-80 TAGGING 60. NEAR THE LAKE,  
TEMPERATURES ARE EXPECTED TO TOP OUT IN THE MID TO UPPER 40S.  
 
PRECIPITATION OUT AHEAD OF THE LOW IS EXPECTED TO BEGIN  
OVERSPREADING THE CWA SOUTH OF I-80 BY LATE MORNING OR EARLY  
AFTERNOON, THEN OVERSPREAD THE I-88 TO I-90 CORRIDOR MID  
AFTERNOON. MODELS HAVE TRENDED SLIGHTLY FARTHER SOUTH, AND IT  
NOW APPEARS THE NORTHERN TIER AND POSSIBLY TWO TIERS OF COUNTIES  
IN ILLINOIS COULD STAY DRY WITH PRECIPITATION MOST LIKELY ACROSS  
THE SOUTH HALF OF THE CWA. VERY WEAK INSTABILITY ONLY CLIPS THE  
FAR SOUTHERN COUNTIES IN THE CWA SO HAVE KEPT THUNDER MENTION  
ALONG AND SOUTH OF THE KANKAKEE RIVER VALLEY.  
 
DEUBELBEISS  
 

 
   
LONG TERM
 
 
243 AM CDT  
 
TUESDAY THROUGH SUNDAY...  
 
A SPRAWLING AREA OF HIGH PRESSURE WILL SPREAD SOUTH FROM THE  
CANADIAN PRAIRIES INTO THE UPPER MIDWEST AND WESTERN GREAT LAKES  
REGION TUESDAY AND WEDNESDAY BRINGING DRY CONDITIONS AND SOME  
PEEKS OF SUNSHINE. NORTH TO NORTHEAST FLOW AND PERSISTENT ONSHORE  
FLOW WILL KEEP TEMPERATURES LOWER NEAR THE LAKE FRONT. LOCAL  
CLIMATE DATA INDICATES THAT DOWNTOWN CHICAGO STRUGGLES TO REACH  
THE MID 40S IN LAKE AUGUST ON DAYS WITH PERSISTENT ONSHORE FLOW.  
HAVE UNDERCUT SOME OF THE GUIDANCE NEAR THE LAKE FRONT KEEPING  
TEMPERATURES IN THE LOW 40S IMMEDIATELY ALONG THE SHORE WHILE  
INLAND TEMPERATURES SHOULD BE ABLE TO WARM INTO THE LOW TO MID  
50S.  
 
MODELS CONTINUE TO COME INTO BETTER AGREEMENT ON AREA OF LOW  
PRESSURE LIFTING ACROSS THE REGION LATE IN THE WEEK. WHILE TIMING  
DIFFERENCES REMAIN MODERATELY LARGE, MODELS ARE NOW HONING IN ON  
A LOW TRACK FROM NEAR ST LOUIS TO NORTHERN INDIANA. DESPITE  
FALLING ON THE COLD SIDE OF THE LOW TRACK, FORECAST SOUNDINGS FROM  
THE GFS INDICATE THE COLUMN WILL BE WARM ENOUGH FOR ALL RAIN.  
MODELS REMAIN IN REASONABLY GOOD AGREEMENT THROUGH SATURDAY  
BUILDING HIGH PRESSURE ACROSS THE MIDWEST, BUT BEGIN TO DIVERGE  
THEREAFTER ON HANDLING A CUTOFF LOW THAT DEVELOPS OVER THE WESTERN  
STATES LATE THIS WEEK INTO THE WEEKEND.  
 
DEUBELBEISS  
 

 
   
AVIATION
 
 
FOR THE 06Z TAFS...  
 
MAIN FORECAST CONCERNS ARE WITH PERSISTENT IFR/LIFR CEILINGS  
THROUGH MUCH OF THE FORECAST PERIOD, FOG AND REDUCED VIS THIS  
MORNING, AND THEN A WIND SHIFT TO THE NORTHEAST LATER THIS  
MORNING.  
 
CEILINGS STEADILY LOWERING ONCE AGAIN AT THIS TIME, WITH IFR  
CEILINGS QUICKLY FALLING TO LIFR. THE ONLY SITE WHICH HAS NOT  
QUITE OBSERVED THIS TREND IS GYY, BUT ANTICIPATE THIS TREND TO  
IMPACT THIS SITE AS WELL OVER THE NEXT 1-2 HOURS. THESE LOWER  
CEILINGS THEN EXPECTED TO BE IN PLACE FOR MUCH OF TODAY. GUIDANCE  
DOES VARY TO THE EXTENT OF ANY IMPROVEMENT LATER TODAY INTO  
TONIGHT, AND HAVE MAINTAINED FORECAST IMPROVEMENT TO MVFR.  
HOWEVER, WILL MONITOR FOR THE POTENTIAL FOR IFR CEILINGS ONCE  
AGAIN LATER TONIGHT. FOG WILL LIKELY LOWER THROUGH EARLY THIS  
MORNING WITH RFD AND DPA LIKELY GETTING INTO THE MORE DENSE FOG,  
WITH VIS BELOW 1 MILE. THIS MAY IMPACT ORD AND MDW, AND WILL NEED  
TO CONTINUE TO MONITOR FOR THIS POTENTIAL. WESTERLY WINDS WILL  
GRADUALLY TURN TO THE NORTHWEST THIS MORNING, AND THEN TO THE  
NORTHEAST BY MID MORNING. SPEEDS SHOULD INITIALLY STAY BELOW 10  
KT, BUT DO ANTICIPATE SPEEDS AT OR ABOVE 10 KT BY EARLY THIS  
EVENING.  
 
RODRIGUEZ  
 

 
   
MARINE
 
 
317 AM CDT  
 
LOW PRESSURE OVER THE CENTRAL GREAT LAKES IS DEPARTING TO THE  
NORTHEAST THIS MORNING, WHILE WEST TO NORTHWEST WINDS ARE IN  
PLACE. EXPECT A TREND TOWARDS THE NORTHWEST FOR MUCH OF THE LAKE  
THIS MORNING, AND THEN MORE NORTHERLY THROUGHOUT TODAY. HOWEVER,  
SPEEDS DON'T APPEAR TO BE TOO STRONG FOR MUCH OF TODAY. VERY MOIST  
CONDITIONS STILL IN PLACE OVER MUCH OF THE LAKE, WITH DENSE FOG  
LIKELY BEING OBSERVED OVER THE ENTIRE LAKE WITH THE EXCEPTION OF  
THE INDIANA NEARSHORE. HAVE THE DENSE FOG ADVISORY IN PLACE  
THROUGH LATER THIS MORNING AND DO THINK THIS END TIME STILL SEEMS  
REASONABLE. WILL NEED TO MONITOR FOR FOG TO POSSIBLY LINGER LONGER  
OVER PORTIONS OF THE LAKE TODAY THOUGH, ESPECIALLY OVER THE  
SOUTHERN END OF THE LAKE. HIGH PRESSURE TO THE NORTHWEST AND LOW  
PRESSURE TRACKING THROUGH THE REGION JUST SOUTH OF THE LAKE  
TONIGHT INTO TUESDAY WILL ALLOW NORTHERLY WINDS TO INCREASE.  
EXPECT SPEEDS OF 15 TO 25 KT WITH SOME GUSTS UP TO 30 KT OVER MUCH  
OF THE LAKE TONIGHT, WITH THESE SPEEDS AND DIRECTION LIKELY  
CONTINUING INTO TUESDAY. THESE STRONGER WINDS AND BUILDING WAVES  
WILL LIKELY PROVIDE CONDITIONS HAZARDOUS TO SMALL CRAFT BY LATE  
TONIGHT AND ESPECIALLY INTO TUESDAY. THESE STRONGER NORTHERLY  
WINDS WILL PERSIST THROUGH MIDWEEK.  
 
RODRIGUEZ  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...DENSE FOG ADVISORY...LMZ740-LMZ741-LMZ742-LMZ777-LMZ779 UNTIL 9  
AM MONDAY.  
 

 
 

 
 
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