699  
FXUS63 KIWX 250520  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
120 AM EDT MON JUN 25 2018  
   
SYNOPSIS
 
 
ISSUED AT 335 PM EDT SUN JUN 24 2018  
 
AN ISOLATED SHOWER IS POSSIBLE THIS EVENING ACROSS SOUTH CENTRAL  
LOWER MICHIGAN AND FAR NORTHWEST OHIO, BUT OTHERWISE DRY  
CONDITIONS ARE EXPECTED FROM TONIGHT THROUGH LATER MONDAY NIGHT.  
THE NEXT SYSTEM TO AFFECT THE AREA WILL BE TUESDAY AND WEDNESDAY  
WHEN SOME LOCALLY HEAVY RAIN IS POSSIBLE ALONG WITH A POTENTIAL OF  
A FEW STRONG STORMS. DRY WEATHER WILL RETURN FOR WEDNESDAY NIGHT,  
BUT HEAT AND HUMIDITY WILL BUILD FOR THURSDAY AND FRIDAY. LOW  
TEMPERATURES TONIGHT WILL RANGE FROM THE MID 50S TO LOWER 60S.  
HIGH TEMPERATURES ON MONDAY WILL RANGE FROM THE MID 70S ACROSS  
SOUTH CENTRAL LOWER MICHIGAN TO THE LOWER 80S ACROSS WEST CENTRAL  
INDIANA.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH MONDAY)  
ISSUED AT 335 PM EDT SUN JUN 24 2018  
 
LARGE SCALE CYCLONIC FLOW CONTINUES ACROSS THE GREAT LAKES REGION  
THIS AFTERNOON. WATER VAPOR IMAGERY INDICATES A WELL DEFINED VORT  
MAX HEADED ACROSS WESTERN LAKE ERIE VICINITY WHICH APPEARS TO BE  
ASSOCIATED WITH MORE CONCENTRATED AREA OF RAIN SHOWERS ACROSS  
SOUTHERN LAKE HURON. WHILE NOT AS EVIDENT ON SATELLITE IMAGERY,  
MODEL INITIALIZATIONS DO SUGGEST PRESENCE OF ANOTHER UPSTREAM  
VORT ACROSS SOUTHERN AND CENTRAL LAKE MICHIGAN WHICH WILL SLOWLY  
DROP SOUTHEAST ACROSS THE REGION TONIGHT. COMBINATION AND  
PROGRESSION OF THESE TWO PERTURBATIONS WILL DRIVE ANOTHER LOW  
LEVEL TROUGH AXIS SOUTHWARD LATE THIS AFTERNOON INTO THIS EVENING.  
VISIBLE SATELLITE IMAGERY STARTING TO INDICATE A MORE WELL  
DEVELOPED CU FIELD FORMING FROM KALAMAZOO TO TOLEDO. MODIFICATION  
OF EARLIER AMDAR SOUNDING ACROSS THE NORTHEAST SUGGESTS MINIMAL  
INSTABILITY ON THE ORDER OF 200-400 J/KG. INSTABILITY LIKELY A BIT  
MORE SUBSTANTIAL FOR LOCATIONS ALONG ROUTE 30 CORRIDOR, ALTHOUGH  
FORCING WILL BE LACKING UNTIL UPSTREAM LAKE MICHIGAN VORT MAX  
SLOWLY SAGS SOUTHEAST INTO THIS EVENING. PREVIOUS FORECAST OF  
SLIGHT CHANCE/LOW CHANCE POPS ACROSS THE EAST/NORTHEAST THROUGH  
EARLY EVENING STILL APPEAR TO BE ON TRACK AND NOT EXPECTING TO  
MAKE MAJOR CHANGES.  
 
LOW RAIN CHANCES WILL DIMINISH AFTER 00Z WITH LOSS OF DIURNAL  
INSTABILITY GIVEN WEAK NATURE TO MID/UPPER LEVEL FORCING.  
OTHERWISE, JUST SOME INCREASED CLOUDS ACROSS THE EAST TO PERSIST  
INTO THIS EVENING WITH VORT PASSAGE BEFORE MAINLY MOSTLY CLEAR  
SKIES FOR REMAINDER OF THE NIGHT. A PUNCH OF DRY LOW LEVEL AIR TO  
BUILD ACROSS THE REGION LATER TONIGHT IN WAKE OF LOW LEVEL TROUGH  
THIS EVENING, WHICH WILL ALLOW MINS TONIGHT INTO THE MID 50S TO  
LOWER 60S.  
 
UPPER RIDING AND ASSOCIATED SFC ANTICYLCONE TO BUILD ACROSS THE  
REGION ON MONDAY WITH ANY SHOWER ACTIVITY REMAINING WELL SOUTH OF  
THE FORECAST AREA. NEAR SEASONABLE TEMPS ARE EXPECTED WITH CONTINUED  
LOW HUMIDITY LEVELS.  
 

 
   
LONG TERM
 
(MONDAY NIGHT THROUGH SUNDAY)  
ISSUED AT 335 PM EDT SUN JUN 24 2018  
 
LATE MONDAY NIGHT WILL MARK THE BEGINNING OF ANOTHER ACTIVE WEATHER  
PERIOD THAT WILL CONTINUE THROUGH WEDNESDAY. A SLOW MOVING UPPER  
LEVEL LOW WILL APPROACH THE REGION FROM THE CENTRAL PLAINS. GUIDANCE  
IS IN GENERAL CONSENSUS OF LEAD SHORT WAVE KICKING OUT OF LARGER  
NEGATIVE HEIGHT ANOMALY EARLY TUESDAY. SOME QUESTION AS TO HOW  
UPSTREAM NOCTURNAL CONVECTION WOULD BE MAINTAINED INTO LOCAL AREA  
FOR FIRST PART OF TUESDAY GIVEN INITIALLY MEAGER INSTABILITY  
PROFILES, ALTHOUGH ADVECTIVE FORCING WILL BE ON THE INCREASE EARLY  
TUESDAY. MID LEVELS SOMEWHAT ON THE WARM SIDE RAISING SOME QUESTIONS  
AS TO EXTENT OF DESTABILIZATION ON TUESDAY, AND A GOOD DEAL OF  
UNCERTAINTY EXISTS WITH HOW OVERNIGHT STORMS WILL MODIFY ENVIRONMENT  
FOR TUESDAY. LATEST 12Z SUITE OF GUIDANCE WOULD SUGGEST GREATEST  
SEVERE POTENTIAL PROBABLY REMAINING JUST WEST OF LOCAL AREA IN PRE-  
FRONTAL TROUGH TYPE ENVIRONMENT CLOSER TO BETTER MID/UPPER LEVEL  
SUPPORT ACROSS MID MS VALLEY. MAY HAVE TO WATCH FOR SOME STRONG/SEVERE  
THREAT INTO AT LEAST WESTERN PORTIONS OF THE AREA LATER TUESDAY  
AFTERNOON/EVENING AS SHEAR PROFILES WILL BE ON THE INCREASE WITH A  
50 KNOT 500 MB SPEED MAX APPROACHING. AGAIN, THE MAIN  
UNCERTAINTIES FOR SEVERE POTENTIAL ARE POSSIBLE UNFAVORABLE  
DIURNAL TIMING TO STRONGEST FORCING AND INSTABILITY MAGNITUDE  
UNCERTAINTY.  
 
POTENTIAL FOR HEAVIEST RAIN WOULD APPEAR TO BE TUESDAY NIGHT INTO  
POSSIBLY EARLY WEDNESDAY AS PRE-FRONTAL TROUGH MOVES IN WITH  
RESPECTABLE 1.75-2 INCH PWATS IN PLACE. THERE SHOULD BE AT LEAST  
SOME DECENT PROGRESSION WITH PRIMARY UPPER LEVEL LOW HOWEVER, WHICH  
MAY ALLEVIATE HIGHER END HEAVY RAIN CONCERNS. WITH RECENT HEAVY  
RAINFALL ACROSS PORTIONS OF THE AREA, DID CONSIDER AN ESF THIS  
AFTERNOON TO HIGHLIGHT TUE/WED FLOOD POTENTIAL, BUT WILL DEFER TO  
LATER SHIFTS WITH STILL A GOOD DEAL OF UNCERTAINTY HOW  
TIMING/INSTABILITY WILL PLAY OUT.  
 
CONDITIONS DRY OUT FOR WEDNESDAY NIGHT AND THURSDAY WITH THE MAIN  
WEATHER STORY BEYOND THIS POINT ON BUILDING HEAT. MEDIUM RANGE  
MODELS HAVE BEEN FAIRLY CONSISTENT IN RIDGE AMPLIFICATION WITH  
LARGER UNCERTAINTY TO WHAT EXTENT TO DAMPEN THE RIDGE LATER NEXT  
WEEKEND WITH NEXT LARGER SCALE WAVE WORKING ACROSS THE NORTHERN TIER  
OF CONUS. HEAT INDICES IN EXCESS OF 100 ARE AT LEAST A POSSIBILITY  
FOR PORTIONS OF THE FRI-SUN PERIOD. WITH UNCERTAINTIES IN TIMING  
THIS NEXT UPPER WAVE NEXT WEEKEND, AND SEVERAL DIFFERENT SOLUTIONS  
ON EXTENT OF RIDGE SUPPRESSION, WILL KEEP THE POST-WED NIGHT  
PERIOD DRY.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)  
ISSUED AT 117 AM EDT MON JUN 25 2018  
 
VFR PREVAILING CONDITIONS EXPECTED FOR THE 06Z TAF CYCLE. THERE  
DOES REMAIN A CHANCE FOR A MVFR STRATUS DECK TO FORM AT THE  
TERMINALS IN THE 10-12Z TIME FRAME, BUT CONFIDENCE IS TOO LOW TO  
GO PREVAILING. OTHERWISE, SURFACE WINDS WILL SLOWLY SHIFT OUT OF  
THE EAST AND SOUTHEAST OVER THE FIRST 12 HOURS OF THIS TAF CYCLE.  
 

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

 
 

 
 
SYNOPSIS...MARSILI  
SHORT TERM...MARSILI  
LONG TERM...MARSILI  
AVIATION...CM  
 
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