068  
FXUS63 KLOT 210014  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
714 PM CDT MON AUG 20 2018  
   
SHORT TERM
 
 
250 PM CDT  
 
LATE AFTERNOON THROUGH TONIGHT  
LOW PRESSURE CONTINUES TO SLOWLY MOVE EAST ACROSS SOUTH-CENTRAL IOWA  
WITH A WARM FRONT ARCHING NEAR PEORIA, PONTIAC AND LAFAYETTE LAST  
HOUR. CLOUD COVER REMAINS ABUNDANT NORTH OF THE BOUNDARY ACROSS  
MOST OF THE FORECAST AREA BUT HAVE SEEN BREAKS OUT THE WINDOW.  
SUNNIER SKIES WITH DEVELOPING CU EXISTS SOUTH OF THE BOUNDARY AND  
WINDS HAVE TURNED SOUTHWESTERLY. THE BOUNDARY WILL CONTINUE  
NORTHWARD INTO THE AREA THROUGH EARLY EVENING. LARGE SCALE ASCENT  
WILL CONTINUE TO GENERATE ISOLATED TO SCATTERED SHOWERS AND  
THUNDERSTORMS WITH THE BEST COVERAGE LIKELY ALONG AND WEST OF THE  
INTERSTATE 39 CORRIDOR OVER THE NEXT FEW HOURS. SOME EXPANSION IS  
EXPECTED EASTWARD INTO NORTHEAST ILLINOIS AND THE CHICAGO METRO  
AREA LATE THIS AFTERNOON INTO EARLY THIS EVENING AS THE FRONT  
PASSES BY.  
 
THE POSSIBILITY FOR SEVERE WEATHER CONTINUES TO BE MONITORED INTO  
THE EVENING. SPC MARGINAL RISK LIKELY REMAINS APPROPRIATE, WITH  
THE MAIN CONCERN BEING A BRIEF TORNADO OR DAMAGING GUST. THE  
PRIMARY INSTABILITY AXIS, WITH SBCAPE AROUND 2000 J/KG OR A BIT  
HIGHER, AT THE PRESENT TIME RUNS FROM NORTH OF THE QUAD CITIES  
INTO THE BLOOMINGTON AREA WHICH IS WHERE SATELLITE SHOWS SOME  
CLEARING AND A BROKEN LINE OF STORMS IS BLOSSOMING ON RADAR. WINDS  
ARE WELL BACKED AHEAD OF THIS LINE, LCLS APPEAR TO BE UNDER 1KM,  
AND 0-1KM SRH IS NEAR 100 M2/S2 ACCORDING TO THE SPC  
MESOANALYSIS WHICH FITS WITH THE 18Z ILX SOUNDING. DEEP LAYER  
SHEAR ALSO IS QUITE MARGINAL, SO WOULD NOT EXPECT PROLONGED  
ORGANIZED CELLS BUT CAN NOT RULE OUT A SHORT LIVED SPINUP.  
 
WITH THE LOW APPROACHING THROUGH THE EVENING, SCATTERED SHOWERS  
AND SOME STORMS WILL PROBABLY CONTINUE ACROSS MUCH OF THE AREA  
THROUGH THE EVENING. A WAVE AHEAD OF THE MAIN UPPER TROUGH AXIS  
WILL TRACK FROM EAST-CENTRAL MISSOURI TO NORTHWEST INDIANA DURING  
THE EVENING BECOMING A FOCAL POINT FOR SHOWERS AND THUNDERSTORMS.  
THIS SUPPORTS THE HIGHEST COVERAGE OF ACTIVITY ALONG AND EAST OF  
I-55 AND PERHAPS A LITTLE FURTHER EAST OR EAST OF I-57 FROM MID  
EVENING THROUGH THE EARLY OVERNIGHT HOURS. THUNDER CHANCES WILL  
DECREASE LATE TONIGHT BUT SCATTERED SHOWERS WILL CONTINUE TO BE  
POSSIBLE BEHIND THE DEPARTING UPPER TROUGH AXIS.  
 
MDB/LENNING  
 

 
   
LONG TERM
 
 
315 PM CDT  
 
TUESDAY THROUGH MONDAY...  
 
THE STRONG LOW PRESSURE SYSTEM WILL ACROSS THE SOUTHERN TIP OF  
LAKE MICHIGAN TUESDAY MORNING. THIS LOW WILL CONTINUE TO  
STRENGTHEN ACROSS THE EASTERN GREAT LAKES ON TUESDAY AS COLDER AIR  
ACROSS THE UPPER MIDWEST SPILL SOUTHWARD BEHIND THE LOW. SOME  
SHOWERS WILL CONTINUE, MAINLY IN THE MORNING, BUT CANNOT RULE OUT  
A FEW IN THE AFTERNOON/EARLY EVENING AS A SECONDARY UPPER LEVEL  
WAVE WILL PASS THROUGH SOUTHERN WISCONSIN. THIS LOW WILL DRIVE A  
REINFORCING COLD FRONT INTO THE AREA TUESDAY NIGHT.  
 
THIS FRONT WILL BRING WITH IT SOME VERY PLEASANT SUMMER WEATHER  
WITH SUNSHINE, SLIGHTLY BELOW AVERAGE TEMPERATURES, AND  
COMFORTABLE HUMIDITY LEVELS WEDNESDAY INTO THURSDAY. MEDIUM RANGE  
MODELS IN REASONABLY GOOD AGREEMENT IN NEXT SHORTWAVE TROUGH  
MOVING ACROSS THE REGION LATE IN THE WEEK WITH SHOWER/T-STORM  
CHANCES RAMPING UP IN SEVERAL WAVES LATER FRIDAY THROUGH EARLY  
SATURDAY MORNING IN ADVANCE OF WARM FRONT SLATED TO MOVE ACROSS  
THE REGION.  
 
HEADING INTO THE WEEKEND AND EARLY NEXT WEEK, THERE IS STILL A FAIRLY  
CONSISTENT SIGNAL FOR ABOVE TO MUCH ABOVE AVERAGE TEMPERATURES IN  
FACT, IT IS LOOKING INCREASINGLY LIKELY THAT WE COULD BE IN LINE  
FOR A LATE SEASON HEAT WAVE, AND THIS WOULD BE COUPLED WITH  
UNCOMFORTABLE HUMIDITY LEVELS ALSO. HIGH PRESSURE ALOFT WILL  
BECOME CENTERED OVER THE MID TO LOWER MISSISSIPPI/OHIO/TENNESSEE  
VALLEYS AND REMAIN ANCHORED THERE INTO MID TO LATE NEXT WEEK. LONG  
TERM MODELS DO GENERALLY AGREE FAIRLY WELL REGARDING THE STRENGTH  
OF THIS HIGH. UNCERTAINTY IN HOW STOUT THE HIGH REMAINS ON ITS NORTHERN  
EXTENT, AND SUBSEQUENTLY THE POTENTIAL "RING OF FIRE" CONVECTION  
SUGGESTS THAT WE HOLD CLOSE TO THE PROGGED BLEND TEMPERATURES,  
THOUGH DID TREND TOWARD EC/GFS BLENDED 925 TEMPERATURE  
CLIMATOLOGY WHICH DOES SUPPORT 90S AREA WIDE BY SUNDAY.  
 
MONDAY HAS THE POTENTIAL FOR PRECIP TO GET IN AND KEEP TEMPS A BIT  
MORE AND CHECK, WE WILL SEE. AND LOOKING BEYOND, IF GFS AND ECMWF  
PROGGED 925MB TEMPS IN THE MID- UPPER 20S CELSIUS WERE TO VERIFY  
AND CONVECTION DOESN'T SHOVE THE EFFECTIVE FRONTAL BOUNDARY  
FARTHER SOUTH, THEN THOSE 925MB TEMPS WOULD CERTAINLY SUPPORT HIGH  
TEMPERATURES SOLIDLY INTO THE 90S. GLANCING BEYOND THE DAY 7  
PERIOD, THE UPPER HIGH DOES APPEAR TO STRENGTHEN, AND MEDIUM RANGE  
GUIDANCE WITH STRONG SUPPORT FROM THEIR RESPECTIVE ENSEMBLES,  
STILL SUGGEST THAT THE HEAT EPISODE WOULD EXTEND THROUGH MID WEEK  
AND POSSIBLY LONGER.  
 
KMD/IZZI  
 

 
   
AVIATION
 
 
FOR THE 00Z TAFS...  
 
THUNDERSTORMS TO IMPACT THE TERMINALS THIS EVENING, AT LEAST FOR  
AN ADDITIONAL TWO TO MAYBE THREE HOURS. THE STORMS APPROACHING  
THE TERMINALS AT THIS TIME ARE ON THE STRONGER SIDE, WITH HEAVY  
RAIN TO LIKELY LOWER VIS TO BRIEFLY AROUND ONE MILE. BEYOND THIS  
PERIOD, COVERAGE WILL LOWER BUT WITH SHOWERS WITH EMBEDDED THUNDER  
STILL TO REMAIN AROUND THE TERMINALS THROUGH LATE EVENING. DO  
EXPECT A FURTHER DIMINISHING TREND IN COVERAGE OF SHOWERS AND  
THUNDERSTORMS THROUGH THE REMAINDER OF THE NIGHT. HOWEVER, WILL  
LIKELY SEE ADDITIONAL ISOLATED PRECIP DEVELOPMENT ON TUESDAY, BUT  
WITH THUNDER LIKELY LIMITED. SCATTERED MVFR CEILINGS WILL REMAIN  
THIS EVENING, BECOMING MORE WIDESPREAD LATE TONIGHT INTO EARLY  
TUESDAY MORNING. STILL A POSSIBILITY FOR IFR CEILINGS, AND WILL  
CONTINUE TO MONITOR THIS CHANCE MAINLY DURING THE EARLY MORNING  
HOURS ON TUESDAY. VARYING WINDS WILL CONTINUE TO VARY OVERNIGHT AS  
AN AREA OF LOW PRESSURE PASSES THROUGH THE AREA, WITH A NORTH  
NORTHEAST DIRECTION THEN LIKELY ON TUESDAY.  
 
RODRIGUEZ  
 

 
   
MARINE
 
 
315 PM CDT  
 
AN UNSEASONABLY STRONG LOW PRESSURE SYSTEM WILL TRACK  
FROM SOUTHERN IOWA TO SOUTHERN LAKE MICHIGAN LATE TONIGHT, TO  
SOUTHEAST ONTARIO TUESDAY AFTERNOON. SE WINDS OF 20-25 KNOTS ARE  
EXPECTED FOR THE SOUTH HALF OF THE LAKE THROUGH THIS EVENING,  
MAINLY AWAY FROM THE INDIANA SHORELINE. THE LOW WILL PASS OVER  
THE LAKE FROM ROUGHLY KENOSHA TO MUSKEGON OVERNIGHT, WITH A  
SUBSEQUENT LULL IN WINDS AND WAVES. BUT CAUTION IS URGED AS N  
WINDS TO 30 KNOTS WITH OCCASIONAL GALES TO 35 KNOTS CAN BE  
EXPECTED ACROSS MUCH OF THE LAKE LATE TONIGHT THROUGH TUESDAY  
EVENING BEHIND THE LOW.  
 
THIS AFTERNOON AND TONIGHT, THUNDERSTORMS ON THE FAR SOUTHERN  
PORTION OF THE LAKE WILL BE CAPABLE OF PRODUCING WATERSPOUTS.  
ADDITIONALLY, SHOWERS ON TUESDAY ACROSS MUCH OF THE LAKE MAY RESULT  
IN A FEW WATERSPOUTS. THUNDERSTORMS THROUGH  
EARLY EVENING MAY ALSO PRODUCE GUSTY AND ERRATIC WINDS.  
 
WINDS WILL GRADUALLY DIMINISH TO UNDER 20 KNOTS BY WEDNESDAY  
AFTERNOON AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION. SW  
WINDS WILL THEN INCREASE TO 25 KNOTS ACROSS THE NORTH HALF BY  
THURSDAY EVENING, AND BECOME SOUTHERLY TO 30 KNOTS ACROSS ALL OF THE  
LAKE FRIDAY AFTERNOON THROUGH INTO SATURDAY AHEAD OF ANOTHER LOW  
PRESSURE TRACKING NE ACROSS THE UPPER MS RIVER VALLEY.  
 
KMD/KLUBER  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014 UNTIL 1 PM WEDNESDAY.  
 
IN...BEACH HAZARDS STATEMENT...INZ001-INZ002...1 PM TUESDAY TO 7 PM  
WEDNESDAY.  
 
LM...SMALL CRAFT ADVISORY...WINTHROP HARBOR TO NORTHERLY IS. UNTIL 1 AM TUESDAY.  
 
SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...10 AM TUESDAY TO  
11 AM WEDNESDAY.  
 
SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...1 PM TUESDAY TO 4  
PM WEDNESDAY.  
 

 
 

 
 
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