154  
FXUS63 KLOT 290518  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
1218 AM CDT MON MAY 29 2017  
   
SHORT TERM
 
 
151 PM CDT  
 
THROUGH MONDAY...  
 
A COLD FRONT HAS PUSHED ACROSS NORTHERN ILLINOIS AND NORTHWEST  
INDIANA EARLIER TODAY WITH CONVECTION EARLY THIS AFTERNOON IN THE  
VICINITY OF THE FRONT, PRIMARILY OVER NORTHERN INDIANA, BUT  
CLIPPING BENTON COUNTY. BEHIND THE FRONT, NORTHWEST WINDS HAVE  
OVERSPREAD MOST OF THE CWA WITH MODEST INSTABILITY IN PLACE, BUT  
WEAKLY CAPPED OR UNCAPPED PER RAP SOUNDINGS. THERE WILL BE TWO  
AREAS TO KEEP AN EYE ON THROUGH THE AFTERNOON AND EVENING FOR  
POTENTIAL SHOWERS AND THUNDERSTORMS. THE FIRST WILL BE ASSOCIATED  
WITH THE LAKE BREEZE IN AND AROUND THE CHICAGO METRO AREA THIS  
AFTERNOON. A STRONG THUNDERSTORM HAS ALREADY DEVELOPED ON THE  
BOUNDARY AND ADDITIONAL ISOLATED SHOWERS AND STORMS WILL BE  
POSSIBLE THROUGH THE AFTERNOON. FARTHER WEST, A SECONDARY SURFACE  
TROUGH IS EVIDENT IN OBS WHILE A CU FIELD HAS DEVELOPED WITHIN THE  
VICINITY OF THE TROUGH THAT STRETCHES FROM CENTRAL WI INTO FAR NW  
IL AN EASTERN IA. THERE IS POTENTIAL FOR ISOLATED TO WIDELY  
SCATTERED CONVECTION AS THIS AREA MOVES ACROSS THE CWA MID TO LATE  
THIS AFTERNOON AND INTO THE EARLY EVENING. WITH ONLY 500-700 J/KG  
MLCAPE AND 20-30KT DEEP LAYER SHEAR IN PLACE, SEVERE THREAT IS  
NOT A BIG CONCERN, BUT CANNOT RULE OUT THE POTENTIAL FOR A FEW  
STORMS TO BECOME STRONG. CLOUD TO GROUND LIGHTNING AND GUSTY WINDS  
WOULD BE A CONCERN FOR ANY OUTDOOR EVENTS.  
 
THREAT FOR PRECIPITATION SHOULD WANE DIURNALLY WITH DRY CONDITIONS  
EXPECTED OVERNIGHT INTO MONDAY MORNING. UPPER LOW IS EXPECTED TO  
PIVOT ACROSS THE WESTERN GREAT LAKES TOMORROW WHILE A SHEARED VORT  
LOBE DROPS INTO NORTHERN ILLINOIS. FORECAST SOUNDINGS TOMORROW  
ARE NOT TOO TERRIBLY DIFFERENT THAN TODAY INDICATING STEEP LOW  
LEVEL LAPSE RATES WITH MODEST INSTABILITY AND LITTLE OR NO  
CONVECTIVE INHIBITION. GIVEN THE FAVORABLE DIURNAL TIMING OF THE  
SHORTWAVE, ANTICIPATE WIDELY SCATTERED SHOWERS AND THUNDERSTORMS  
WILL ONCE AGAIN BE A POSSIBILITY. TEMPERATURES WILL ALSO BE  
FAIRLY SIMILAR TOMORROW WITH HIGHS IN THE MID 70S. DEEP MIXING AND  
BREEZIER CONDITIONS WILL BE IN PLACE THOUGH, SO THERE IS A LOWER  
LIKELIHOOD OF A LAKE BREEZE.  
 
DEUBELBEISS  
 

 
   
LONG TERM
 
 
213 PM CDT  
 
MONDAY NIGHT THROUGH SUNDAY...  
 
THE UPPER LEVEL TROUGH SPREADS OVER THE REGION MONDAY NIGHT. COOLER  
AIR WILL LEAD TO LOWS IN THE LOW 50S. SOUNDINGS ARE PRETTY DRY SO  
KEPT A DRY FORECAST GOING AFTER ANY LINGERING SHOWERS EXIT TO THE  
EAST MONDAY EVENING. ANOTHER VORTICITY STREAMER ROTATES AROUND THE  
UPPER LEVEL LOW AND IT MAY KICK OFF SHOWERS AND STORMS TUESDAY  
AFTERNOON. TUESDAY WILL ALSO BE COOLER WITH HIGHS AROUND 70.  
 
HIGH PRESSURE BUILDS OVER THE PLAINS TUESDAY NIGHT AND WEDNESDAY,  
AND THE UPPER LEVEL LOW SLOWLY SHIFTS EAST. WEDNESDAY WILL BE  
DRY AND COOLER DAY WITH HIGHS AROUND 70.  
 
MY CONFIDENCE IS LOWER WHEN IT COMES TO THURSDAY'S FORECAST. THE  
GFS FEATURES A SHORTWAVE TROUGH AND CONVECTION SPREADING ACROSS THE  
REGION THURSDAY AFTERNOON. THE 12Z EMCWF, ON THE OTHER HAND, HAS A  
MUCH SUBTLER WAVE, BUT DOES HAVE A LITTLE QPF THURSDAY AFTERNOON.  
DECIDED TO KEEP A CHANCE OF SHOWERS AND STORMS IN FOR THURSDAY, BUT  
THINK THE GFS IS SUFFERING FROM CONVECTIVE FEEDBACK. WARMER AIR  
MOVES IN ALOFT, BUT NOT SURE HOW MUCH CLOUD COVER WE WILL HAVE, SO  
KEPT TEMPS IN THE 70S.  
 
LATE THIS WEEK LOOKS ACTIVE WITH MANY PERIODS OF SHOWERS AND STORMS.  
A LOW IS FORECAST TO FORM AND MOVE THROUGH THE MIDWEST SATURDAY  
NIGHT WITH ANOTHER PUSH OF COOLER AIR MOVING IN BEHIND IT SUNDAY.  
 
JEE  
 

 
   
AVIATION
 
 
FOR THE 06Z TAFS...  
 
GUSTY WEST WINDS AND SLIGHT CHANCE POTENTIAL FROM ISOLATED TO  
SCATTERED LATE AFTERNOON SHRA ARE THE MAIN AVIATION FOCUS FOR  
THIS TAF PERIOD.  
 
SECONDARY COLD FRONTAL BOUNDARY NOTED ACROSS EASTERN IOWA, WHICH  
WILL MOVE EAST ACROSS THE MISSISSIPPI THIS MORNING AND RESULT IN A  
WIND SHIFT FROM LIGHT SOUTHWEST TO WEST WINDS ACROSS THE  
TERMINALS AFTER SUNRISE. OTHER THAN SOME PATCHY SCT-BKN MID LEVEL  
VFR CLOUDS, NO SIG WEATHER EXPECTED. DIURNAL DEEPENING OF THE  
BOUNDARY LAYER WILL INCREASE WINDS BEHIND THE FRONT DURING THE  
DAY, WITH GUSTS IN THE 25-30 KT RANGE EXPECTED THIS AFTERNOON.  
COOLER AIR ALOFT, COMBINED WITH AFTERNOON HEATING AND A SERIES OF  
MINOR MID-LEVEL DISTURBANCES, WILL LIKELY RESULT IN A SCT-BKN  
STRATOCU FIELD DEVELOPING BY MID-LATE AFTERNOON, WITH ISOLATED TO  
SCATTERED SHOWERS DEVELOPING ESPECIALLY NORTH AND WEST OF THE  
TERMINALS. WHILE A FEW OF THESE SHOWERS COULD IMPACT THE TAF  
SITES, THE CURRENT EXPECTATION IS THAT COVERAGE WILL BE LOW ENOUGH  
TO NOT INCLUDE IN POINT FORECASTS AT THIS TIME. GUSTY WEST WINDS  
WILL DIMINISH TOWARD SUNSET.  
 
RATZER  
 

 
   
MARINE
 
 
213 PM CDT  
 
WINDS BECOME WEST OVERNIGHT AND INCREASE TO 15-25 KT MONDAY. ISSUED  
A SMALL CRAFT ADVISORY FOR GUSTY WINDS MONDAY FOR POINTS NORTH OF  
GARY, INDIANA. WINDS WILL BE 15-25 KT EAST OF GARY, IN, BUT DO NOT  
HAVE ENOUGH CONFIDENCE IN PERSISTENT 20-25 KT WINDS.  
 
WEST TO SOUTHWEST WINDS OF 15-25 KT ARE EXPECTED THROUGH WEDNESDAY  
NIGHT AS A LOW OVER ONTARIO SLOWLY DRIFTS NORTH TO JAMES BAY. HIGH  
PRESSURE BUILDS OVER THE PLAINS TUESDAY NIGHT AND THEN SHIFTS SOUTH  
OF THE LAKE WEDNESDAY NIGHT. WINDS BECOME NORTH BEHIND A COLD FRONT  
FRIDAY.  
 
JEE  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...10 AM  
MONDAY TO 7 PM MONDAY.  
 

 
 

 
 
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