791  
FXUS63 KIWX 181949  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
349 PM EDT WED SEP 18 2019  
   
SYNOPSIS
 
 
ISSUED AT 348 PM EDT WED SEP 18 2019  
 
DRY AND WARM CONDITIONS WILL PERSIST INTO FRIDAY. CLOUDS WILL  
BEGIN TO INCREASE ON SATURDAY, WITH SHOWERS AND THUNDERSTORMS  
BECOMING LIKELY SATURDAY NIGHT THROUGH SUNDAY NIGHT. SOME LOCALLY  
HEAVY RAINFALL IS POSSIBLE DURING THIS PERIOD. LOW TEMPERATURES  
TONIGHT WILL DROP INTO THE MID AND UPPER 50S. HIGH TEMPERATURES ON  
THURSDAY WILL REACH INTO THE LOW TO MID 80S.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY)  
ISSUED AT 348 PM EDT WED SEP 18 2019  
 
QUIET WEATHER TO CONTINUE IN THE SHORT TERM AS UPPER LEVEL RIDGING  
ACROSS CENTRAL CONUS CONTINUES TO DOMINATE.  
 
SEVERAL WEAK SHORT WAVES CONTINUE TO TOP THE UPPER RIDGE THIS  
AFTERNOON, WITH DEEPER MOISTURE AND ONGOING CONVECTION LIMITED TO  
CORN BELT. UPPER LEVEL WAVE PATTERN WILL NOT CHANGE SIGNIFICANTLY  
OVER THE NEXT FEW DAYS WITH AFOREMENTIONED UPPER WAVES DOING VERY  
LITTLE TO DAMPEN THE AMPLITUDE OF THE UPPER LEVEL RIDGE. DRY LOW  
LEVELS SHOULD FAVOR ANOTHER NIGHT OF LARGE DIURNAL SWINGS AND LOW  
TEMPERATURES BACK INTO THE MID-UPPER 50S.  
 
FOR THURSDAY, NEXT WEAKER UPPER LEVEL SHORT WAVE ACROSS THE  
CENTRAL ROCKIES WILL TOP THE RIDGE AND REACH THE WESTERN GREAT  
LAKES REGION THURSDAY NIGHT. GUIDANCE CONTINUES TO INDICATE WEAK  
WARM FRONTAL-LIKE FEATURE LIFTING NORTHWARD THURSDAY AFTERNOON  
INTO THURSDAY EVENING MARKING THE BEGINNING OF A PERIOD OF  
INCREASING LOW LEVEL MOISTURE TRANSPORT. STILL EXPECTING MOSTLY  
SUNNY SKIES FOR THURSDAY GIVEN EXPECTATION OF CAPPING TO HOLD,  
WITH JUST POSSIBLE INCREASING DIURNAL CU ACROSS THE SOUTH WHERE  
BETTER DEW POINT RECOVERY IS EXPECTED ASSOCIATED WITH THE WARM  
FRONT/WEAK SFC TROUGH FEATURE. DESPITE RELATIVELY SHALLOW MIXING  
LIMITED TO AROUND 900 MB, MUCH ABOVE NORMAL TEMPERATURES ARE  
EXPECTED THURSDAY GIVEN LOW LEVEL THERMAL PROGS AND GOOD  
INSOLATION.  
 

 
   
LONG TERM
 
(THURSDAY NIGHT THROUGH WEDNESDAY)  
ISSUED AT 348 PM EDT WED SEP 18 2019  
 
FOR THURSDAY NIGHT AND BEYOND FOCUS WILL SHIFT TO THE WEST AS  
LONGWAVE EASTERN PACIFIC UPPER TROUGH BECOMES THE EVENTUAL MAIN  
WEATHER PRODUCER BY LATER IN THE WEEKEND. INITIAL WEST-EAST  
ORIENTED POOLED MOISTURE AXIS WILL LIFT NORTHWARD ACROSS GREAT  
LAKES SATURDAY, WITH RENEWED STRONGER LOW LEVEL MOISTURE TRANSPORT  
LIKELY HOLDING OFF FROM WEST TO EAST LATE SATURDAY AFTERNOON INTO  
SATURDAY NIGHT. THIS MOISTURE TRANSPORT WILL BE ENHANCED BY  
STRONGER SOUTHWESTERLY LOW LEVEL FLOW AND NORTHWARD ADVECTION OF  
TROPICAL AIR MASS FROM THE LOWER MS VALLEY/GULF OF MEXICO REGION.  
GUIDANCE CONTINUES TO INDICATE PWATS INCREASING INTO THE 1.75 TO 2  
INCH RANGE LATER SATURDAY NIGHT AND WARM CLOUD DEPTHS RISING TO  
AROUND 12K FEET. WITH LEAD SHORT WAVE KICKING NORTHEAST ACROSS THE  
UPPER MS VALLEY AND THE ABOVE FACTORS, CONCERN EXISTS FOR SOME  
LOCALLY HEAVY RAINFALL SATURDAY NIGHT INTO SUNDAY.  
 
MAIN ITEM OF UNCERTAINTY IN THIS FORECAST DEALS WITH PHASING ISSUES  
OF UPSTREAM FORCING, AND HOW QUICKLY LEAD SHORT WAVE PHASES WITH  
ANOTHER NEGATIVE UPPER HEIGHT ANOMALY DROPPING ACROSS SOUTH  
CENTRAL CANADA. IF BETTER PHASING CAN OCCUR AND SLOWER EVOLUTION  
OF FORCING OCCURS, HEAVY RAIN THREAT WOULD EXTEND INTO LATE SUNDAY  
OR SUNDAY NIGHT. BY LATER SUNDAY EXPECTING ANOMALOUS MOISTURE  
AXIS TO START TO GET PINCHED OFF FROM LOWER LATITUDE CONNECTION AS  
LARGE SCALE UPPER TROUGH WORKS ACROSS THE GREAT LAKES AND FLOW  
STARTS TO BECOME MORE PARALLEL TO THE ASSOCIATED COLD FRONT. STILL  
EARLY TO TALK ABOUT SEVERE POTENTIAL, AND STILL SOME QUESTION AS  
TO HOW MUCH INSTABILITY CAN BE REALIZED GIVEN LIKELY MOIST  
ADIABATIC MID LEVEL LAPSE RATES. IF SLOWER EVOLUTION IS REALIZED,  
PERHAPS SOME LOW END SEVERE THREAT CANNOT BE RULED OUT SUNDAY  
GIVEN INCREASING SHEAR PROFILES, BUT HYDRO AND RAIN AMOUNTS WILL  
LIKELY BE THE MAIN CONCERN WITH THIS SYSTEM. ANTECEDENT CONDITIONS  
ARE QUITE DRY ACROSS MOST AREAS, WHICH COULD LIMIT OVERALL FLOOD  
THREAT. WILL NEED TO WATCH THIS PERIOD OVER THE NEXT FEW DAYS  
HOWEVER, GIVEN SUCH ANOMALOUS MOISTURE ADVECTING INTO THE REGION.  
 
FRONT SHOULD SLOW OR STALL JUST SOUTH OF THE AREA FOR EARLY NEXT  
WEEK WHICH COULD MAKE REGION SUSCEPTIBLE TO SOME ADDITIONAL  
CHANCES OF RAIN BY THE TUE-WED PERIOD WITH TEMPERATURES CLOSER TO  
SEASONAL NORMS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)  
ISSUED AT 119 PM EDT WED SEP 18 2019  
 
HIGH PRESSURE OVER THE REGION WILL RESULT IN VFR CONDITIONS AND  
LIGHT ESE WINDS FOR THE DURATION OF THE 18Z TAF CYCLE.  
 

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

 
 

 
 
SYNOPSIS...MARSILI  
SHORT TERM...MARSILI  
LONG TERM...MARSILI  
AVIATION...MF  
 
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