455  
FXUS63 KLOT 211145  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
645 AM CDT THU JUN 21 2018  
   
SHORT TERM
 
 
330 AM CDT  
 
THROUGH FRIDAY...  
 
SLOW MOVING UPPER LEVEL LOW PRESSURE IN A RELATIVELY HIGH  
PRECIPITABLE WATER ENVIRONMENT WILL MAKE FOR MESSY COUPLE OF DAYS  
FOR SOME AREAS ACROSS OUR REGION. EXPECT COOL AND WET CONDITIONS,  
WITH AREAS UNDER AND CLOSER TO THE LOW GETTING BREAKS/SHOWERY  
WEATHER, AND AREAS FARTHER NORTH POTENTIALLY GETTING STUCK IN  
EXTENDED PERIODS OF RAIN WITH EMBEDDED THUNDER. HEAVY RAIN AND  
LOCALIZED FLOODING APPEAR THE MAIN CONCERN, AND WITH LOW FLASH  
FLOOD GUIDANCE DUE TO WET GROUNDS, FLASH FLOODING MAY BECOME AN  
ISSUE FOR SOME AREAS AS WELL.  
 
THE 0Z ILX SOUNDING DEPICTS THE MOIST AND RELATIVELY WARM AIRMASS,  
WITH A 1.89" PWAT AND 13,500 FT FREEZING LEVEL. THIS IS A GOOD  
ENVIRONMENT FOR EFFICIENT WARM RAIN PROCESSES. INSTABILITY DOES  
LOOK TO REMAIN A BIT MORE TEMPERED THE NEXT FEW DAYS WITH ALL OF  
THE CLOUD COVER. BUT WITH EVEN LOWER INSTABILITY, EMBEDDED THUNDER  
REMAINS POSSIBLE WHICH WILL ENHANCE THE WARM RAIN PROCESSES.  
CERTAINLY WITH MORE INSTABILITY THIS BECOMES EVEN MORE CONCERNING.  
 
THE FIRST WAVE WILL COME THROUGH THE AREA THIS MORNING INTO EARLY  
AFTERNOON. THESE WILL CERTAINLY HAVE HEAVY RAIN AND MAYBE SOME  
LOCALIZED FLOODING POTENTIAL, BUT THIS AXIS MAY BE A BIT MORE  
PROGRESSIVE THAN WHAT MAY BE COMING LATER TONIGHT. AREAS SOUTH OF  
I-80 MAY GET IN ON SOME BREAKS TODAY, AND AS SUCH WILL  
DESTABILIZE A BIT MORE. AS THE UPPER LOW CONTINUES TO SHIFT EAST,  
ADDITIONAL SHORTWAVES WILL PINWHEEL AHEAD OF THE LOW. PNT FORECAST  
SOUNDINGS DEPICT UP TO 1000 J/KG OF CAPE AND 25 KT OF SHEAR WITH  
DECENT LOW LEVEL LAPSE RATES SUPPORTING SOME LOCALIZED STRONGER  
WIND GUSTS IN OUR SOUTHERN COUNTIES. MID LEVEL LAPSE RATES ARE  
WEAKER, THUS THE SEVERE COVERAGE DOES NOT APPEAR TO BE THAT LARGE,  
WITH INSTABILITY DROPPING OFF FARTHER NORTH, BUT IT APPEARS THAT  
SOME STRONGER STORMS WILL BEAR WATCHING ACROSS WEST CENTRAL IL AND  
CLOSE TO OUR AREA LATER THIS AFTERNOON.  
 
TONIGHT THE UPPER LOW WILL BUILD INTO SOUTH CENTRAL IL. THIS WILL  
SETUP AND EASTERLY FEED INTO THE AREA, AND THEREFORE STORMS WILL  
LIKELY TRAIN OVER SIMILAR AREAS WHEREVER THE HIGHER THETA-E AXIS  
ON THE BACK SIDE OF THE SYSTEM SETS UP. MODEL RUN ACCUM QPF  
CERTAINLY SUGGESTS MANY AREAS WHEN ALL IS SAID AND DONE WILL SEE  
IN EXCESS OF AN INCH, WITH 3-4" TOTALS NOT OUT OF THE QUESTION IN  
THIS SETUP. THE CHALLENGE WILL BE WHERE THIS HIGHER AXIS WILL BE.  
AT THIS POINT AREAS ALONG AND NORTH OF CHICAGO ARE FAVORED. GEFS  
PLUMES FOR ORD HAVE 1.2 TO 4.5 INCHES OF QPF INDICATING THE  
POTENTIAL THIS SYSTEM HAS FOR SOME AREAS, WITH MEAN CURRENTLY  
HOLDING AT 2.75".  
 
WITH ALL THAT IN MIND, SOME TYPE OF FLOOD MESSAGE IS WARRANTED  
GIVEN THAT RIVERS ACROSS NORTHERN IL ARE RUNNING HIGH, STORM TOTAL  
QPF RANGING FROM 1-5" BOTH FROM RAW GUIDANCE AND GEFS ENSEMBLES  
(SHOWING POTENTIAL IS THERE) WILL GO OUT WITH A FLASH FLOOD  
WATCH THROUGH TONIGHT, THAT MAY NEED TO BE HONED IN LOCATION.  
RIVERS WILL LIKELY RISE AFTER GETTING A GOOD BUMP ALREADY FROM  
RECENT RAINS. WHILE RATES MAY NOT BE AT THE LEVELS FOR FLASH  
FLOODING OR ALL AREAS (AND THE POTENTIAL FOR SOME INITIAL  
BREAKS), THE POTENTIAL IS THERE, ESPECIALLY IF THESE GET OVER MORE  
URBAN AREAS.  
 
KMD  
 

 
   
LONG TERM
 
 
329 AM CDT  
 
FRIDAY THROUGH WEDNESDAY...  
 
NOT TOO MANY CHANGES TO THE BLENDED MODEL GUIDANCE GIVEN THE  
ACTIVE SHORT TERM WEATHER. THE UPPER LOW WILL PULL AWAY FRIDAY  
NIGHT, WITH THE HEAVIER RAINS EASING FRIDAY AFTERNOON AND EVEN  
MORE SO IN THE EVENING. ZONAL FLOW OVER THE WEEKEND AND NORTHEAST  
LOW LEVEL FLOW WITH NO SIGNIFICANT WAVES SUGGESTS SOMEWHAT COOLER  
BUT GENERALLY DRY WEATHER. CANNOT RULE OUT SOME RAIN SHOWERS AT  
TIMES AS THERE IS SOME WEAK ENERGY IN THE ZONAL/NW FLOW ALOFT.  
 
RIDGING ALOFT AND SE FLOW SUGGESTS MONDAY WILL BE DRY WITH SOME  
WARMING. ANOTHER UPPER LOW WILL CROSS THE PLAINS AND ARRIVE ACROSS  
OUR REGION MID WEEK, SUGGESTING MORE INCLEMENT WEATHER IS  
POSSIBLE, DEPENDING ON IF THE LOW MOVES THROUGH OUR AREA OR IF IT  
STAYS NORTH. BEYOND THAT TIME FRAME, THERE ARE HINTS OF A HEAT  
DOME BUILDING IN OUR NEAR THE REGION, BUT IT IS NOT A CLEAN ONE  
THAT MAY BE MUDDLED WITH CLOUDS AND OCCASIONAL PRECIP. DID NUDGE  
TEMPS UP A TAD CLOSER TO 925 MB CLIMATOLOGY.  
 
KMD  
 

 
   
AVIATION
 
 
FOR THE 12Z TAFS...  
 
645 AM...FORECAST CONCERNS REMAIN PERIODS OF MODERATE/HEAVY RAIN  
AND ASSOCIATED CIGS/VIS ALONG WITH LOW POTENTIAL FOR THUNDER.  
 
FORECAST TRENDS APPEAR ON TRACK AS MODERATE RAIN IS NOW DEVELOPING  
ACROSS EASTERN IL. THIS ACTIVITY WILL LIFT NORTH ACROSS THE  
CHICAGO AREA TERMINALS THIS MORNING WITH PERIODS OF HEAVY RAIN  
POSSIBLE. ONLY MEDIUM CONFIDENCE FOR HOW FAR NORTHWEST THIS  
ACTIVITY WILL EXTEND INTO THE RFD AREA. NOT MUCH THUNDER WITH THIS  
ACTIVITY AND NOT EXPECTING MUCH BUT AN ISOLATED THUNDERSTORM IS  
STILL POSSIBLE SO MAINTAIN VICINITY MENTION FOR NOW BUT CHANCES AT  
THE TERMINALS ARE LOW. BETTER CHANCES FOR THUNDER WILL REMAIN  
ACROSS CENTRAL IL AND MAINLY THIS AFTERNOON/EVENING. TIMING ANY  
LULLS IN THE PRECIP WILL REMAIN CHALLENGING BUT THERE IS STILL A  
CONSISTENT SIGNAL FOR A LULL LATER THIS AFTERNOON INTO EARLY THIS  
EVENING WITH ANOTHER AREA OF MODERATE/POSSIBLY HEAVY RAIN LATE  
THIS EVENING INTO THE OVERNIGHT HOURS. CONFIDENCE FOR TIMING AND  
LOCATION STEADILY DECREASE FURTHER OUT INTO THE FORECAST. SHOWERS  
WILL LIKELY PERSIST INTO FRIDAY MORNING.  
 
VISIBILITIES HAVE LOWERED INTO THE 1-3SM RANGE EVEN IN AREAS OF  
LITTLE RAIN CURRENTLY. ITS POSSIBLE VIS REMAINS 1-2SM FOR MUCH OF  
THE DAY BUT CONFIDENCE ON PREVAILING VIS IS LOW. CIGS ARE MAINLY  
IFR/LIFR AND SHOULD SLOWLY LIFT THROUGH IFR AND POSSIBLY LOW MVFR  
LATER THIS MORNING. THERE WILL LIKELY BE SOME VARIABILITY WITH  
CIGS AS PRECIP INTENSITY CHANGES. CIGS WILL LIKELY SETTLE INTO  
LOW MVFR THIS AFTERNOON IF THE LULL IN PRECIP DEVELOPS AND REMAIN  
LOW MVFR FOR THE REST OF THE PERIOD...WITH IFR POSSIBLE.  
 
EASTERLY WINDS WILL STEADILY INCREASE THIS MORNING INTO THE  
12-16KT RANGE WITH GUSTS POSSIBLY AS HIGH AS LOWER 20KTS FROM  
LATE THIS MORNING INTO THIS EVENING. WINDS WILL SLOWLY TURN MORE  
NORTHEASTERLY OVERNIGHT INTO FRIDAY MORNING WITH SPEEDS EXPECTED  
TO REMAIN 10-15KTS. CMS  
 

 
   
MARINE
 
 
416 AM...LOW PRESSURE OVER IA THIS MORNING WILL MOVE TO CENTRAL  
IL FRIDAY MORNING AND THEN TO NEAR LAKE ERIE ON SATURDAY. THIS  
WILL ALLOW AN EASTERLY GRADIENT TO STEADILY INCREASE TODAY INTO  
TONIGHT WITH A PERIOD OF 20-25KT EASTERLY WINDS EXPECTED ON THE  
SOUTHERN PORTION OF LAKE MICHIGAN. SOME HIGHER GUSTS TO 30KTS ARE  
ALSO POSSIBLE...LIKELY ON THE FAR SOUTHERN PART OF THE LAKE. THESE  
WINDS WILL TURN MORE NORTHEASTERLY ON FRIDAY AND THEN DIMINISH  
FRIDAY NIGHT AS THEY SHIFT NORTHERLY. NORTHERLY WINDS WILL THEN  
PERSIST INTO SUNDAY WHEN A COLD FRONT WILL MOVE SOUTH ACROSS THE  
REGION. THIS FRONT WILL MAINTAIN NORTHERLY WINDS...WHICH WILL  
LIKELY INCREASE IN SPEED BEHIND THE FRONT. HIGH PRESSURE IS THEN  
EXPECTED TO MOVE ACROSS THE GREAT LAKES MONDAY AND THEN STEADILY  
SHIFT EAST TUESDAY. CMS  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...FLASH FLOOD WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-  
ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022  
UNTIL 7 AM FRIDAY.  
 
BEACH HAZARDS STATEMENT...ILZ006-ILZ014...7 PM THURSDAY TO 4 AM  
SATURDAY.  
 
IN...BEACH HAZARDS STATEMENT...INZ001...7 PM THURSDAY TO 4 AM  
SATURDAY.  
 
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744...7 PM  
THURSDAY TO 4 AM SATURDAY.  
 

 
 

 
 
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