168  
FXUS63 KIWX 182342  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
742 PM EDT WED JUL 18 2018  
   
SYNOPSIS
 
 
ISSUED AT 300 PM EDT WED JUL 18 2018  
 
HIGH PRESSURE WILL PROVIDE FAIR WEATHER AND LOW HUMIDITY THROUGH  
THURSDAY. LOWS TONIGHT WILL BE IN THE UPPER 50S WITH AFTERNOON  
HIGHS TOMORROW IN THE MID 80S. A LOW PRESSURE SYSTEM WILL THEN  
MOVE INTO THE GREAT LAKES REGION FRIDAY AND STALL THIS WEEKEND  
WITH PERIODIC CHANCES FOR SHOWERS AND THUNDERSTORMS.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY)  
ISSUED AT 300 PM EDT WED JUL 18 2018  
 
MIDLEVEL AVA AND ASSOCIATED SUBSIDENCE WILL REMAIN ANCHORED OVER  
THE GREAT LAKES THROUGH TOMORROW. RIDGE AXIS DOES PASS OUR  
LONGITUDE DURING THE DAY TOMORROW AND WILL ALLOW FOR SOME MINOR  
WAA WITH INCREASINGLY SOUTHERLY FLOW. THIS WILL ALLOW US TO TACK  
ON A FEW EXTRA DEGREES WITH HIGHS APPROACHING THE MID 80S UNDER  
PARTLY CLOUDY SKIES. OVERNIGHT LOWS SIMILAR TO LAST  
NIGHT...PERHAPS A FEW DEGREES WARMER IN SPOTS DUE TO SLIGHTLY  
WARMER PROFILES.  
 

 
   
LONG TERM
 
(THURSDAY NIGHT THROUGH WEDNESDAY)  
ISSUED AT 300 PM EDT WED JUL 18 2018  
 
SITUATION CHANGES SUBSTANTIALLY THURSDAY NIGHT AS LEAD THETA-E RIDGE  
ARRIVES FROM APPROACHING CLOSED MIDLEVEL CIRCULATION ON CYCLONICALLY  
SHEARED SIDE OF SEASONABLY STRONG UPPER LEVEL JET. THIS JET WILL  
CONTINUE TO DIG SOUTH THROUGH THE WEEKEND AND BECOME INCREASINGLY  
CUTOFF FROM MAIN WESTERLIES ALONG US/CANADA BORDER...LEAVING OUR CWA  
IN A REGION OF PERSISTENT LOW/MIDLEVEL CYCLONIC FLOW WITH PERIODIC  
SHOWERS AND POSSIBLY A FEW STORMS.  
 
PRECIP CHANCES BEGIN THU NIGHT THOUGH WILL STILL BE A VERY DRY AND  
STABLE AIRMASS IN PLACE...WITH RELATIVELY WEAK LLJ/MOISTURE  
CONVERGENCE IN ALL BUT OUR FAR W/SW CWA LATE. CHANCES INCREASE  
DURING THE DAY FRI WITH SOME DIURNAL INSTABILITY CONTRIBUTION AND  
APPROACH OF MIDLEVEL VORT LOBE. LATEST 12Z ECMWF HAS TRENDED TOWARD  
THE NAM AND GFS OF A FURTHER SOUTH TRACK...SO TRENDED THE FORECAST  
IN THAT DIRECTION. LIKELY POPS EASILY WARRANTED GIVEN CVA FORCING  
AND DECENT MOISTURE/INSTABILITY...THOUGH WIDESPREAD MODEL QPF MAY  
STILL BE A BIT OVERDONE. EXACT NORTHWARD EXTENT OF MAIN INSTABILITY  
PLUME STILL A BIT UNCERTAIN...BUT A FEW STRONG STORMS POSSIBLE IN  
OUR FAR S/SW BASED ON CURRENT LOW TRACK/TIMING.  
 
A MORE STABLE SCENARIO OVER THE WEEKEND AS VERTICALLY STACKED LOW  
WOBBLES NEAR/JUST SOUTH OF CWA. NOT EXPECTING ANY SEVERE WEATHER BUT  
ENOUGH LOW LEVEL MOISTURE AND DAYTIME HEATING TO SUPPORT A DIURNAL  
COMPONENT TO HIGHEST POPS. BEST CHANCES CURRENTLY APPEAR TO BE SAT  
AS LOW PRESSURE DRIFTS SE OF AREA ON SUN. CHANCES LINGER OVER SE ON  
MONDAY BUT SHOULD START TO SEE SOME GRADUAL CLEARING AS UPPER LOW  
SLOWLY DISSIPATES.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)  
ISSUED AT 737 PM EDT WED JUL 18 2018  
 
HIGH PRESSURE CENTERED OVER MICHIGAN WILL SLOWLY DRIFT EAST  
OVERNIGHT WHILE A SFC LOW MOVES EAST ACROSS THE CENTRAL PLAINS TO  
IOWA BY THURSDAY AFTN. WINDS WILL TURN MORE SOUTHEASTERLY  
TOMORROW AND INCREASE TO AROUND 10 KTS. EXPECT A DIURNAL CU FIELD  
TO ONCE AGAIN DEVELOP DURING THE LATE MORNING HOURS. NO PRECIP IS  
EXPECTED THROUGH THE FCST PERIOD.  
 

 
   
IWX WATCHES/WARNINGS/ADVISORIES
 
 
IN...NONE.  
MI...NONE.  
OH...NONE.  
LM...NONE.  

 
 

 
 
SYNOPSIS...AGD  
SHORT TERM...AGD  
LONG TERM...AGD  
AVIATION...MF  
 
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