930  
FXUS63 KIWX 211013  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
613 AM EDT FRI JUL 21 2017  
   
SYNOPSIS
 
 
ISSUED AT 400 AM EDT FRI JUL 21 2017  
 
EARLY MORNING THUNDERSTORMS SOUTH OF A LAPORTE TO MARION LINE WILL  
EXIT SHORTLY AFTER SUNRISE. CLEARING WILL SLOWLY TAKE PLACE  
THROUGH THE DAY, ESPECIALLY ACROSS NORTHEAST SECTIONS OF THE AREA  
BY THIS AFTERNOON. HIGH TEMPERATURES WILL QUICKLY JUMP INTO THE  
MIDDLE TO UPPER 80S WHERE CLEARING OCCURS. A FEW SPOTS MAY REACH  
90 IF ENOUGH SUNSHINE IS REALIZED. STORMS ARE EXPECTED TO DEVELOP  
ACROSS MINNESOTA AND WISCONSIN AND TRACK TOWARDS THE AREA TONIGHT  
INTO SATURDAY MORNING BRINGING INCREASED CHANCES FOR STRONG TO  
POSSIBLY SEVERE STORMS AND HEAVY RAINFALL TO PARTS OF THE AREA.  
 

 
   
UPDATE
 
 
ISSUED AT 607 AM EDT FRI JUL 21 2017  
 
GRID UPDATE TO EXTEND CATEGORICAL POPS FURTHER SE FOR A FEW HOURS  
AS CONVECTIVE COMPLEX CHARGING MUCH FURTHER SE THAN EXPECTED. NO  
CONCERNS FOR SEVERE WEATHER AS WIND GUST HAVE BEEN IN THE 30 TO 40  
MPH RANGE. MCV WORKING SOUTHEAST RIGHT BEHIND THE AREA OF RAIN AND  
STORMS STIRRING UP SOME INCREASED THUNDERSTORMS ACTIVITY THAT MAY  
REMAIN JUST SOUTH OF THE AREA. INTERESTINGLY ENOUGH, DESPITE THE  
PASSAGE OF THE MCV AND WHAT WOULD NORMALLY BE A LULL IN PRECIP A  
NARROW BROKEN LINE OF STORMS HAS DEVELOPED FROM EASTERN IOWA BACK  
INTO SE SOUTH DAKOTA WHERE FRONTAL BOUNDARY WAS SURGING BACK  
NORTH. NOT SURE WHAT IF ANY IMPACTS THIS MAY HAVE FURTHER DOWN  
STREAM, ESPECIALLY THE ACTIVITY IN EASTERN IOWA. STILL KEEPING  
WITH A DOWNWARD TREND IN POPS INTO THE MORNING.  
 
LAST CHANGE MADE WAS A FEW HOURS OF PATCHY FOG IN THE NE WHERE  
MOSTLY CLEAR SKIES AND LOW TEMP/DEWPOINT DEPRESSION HAS ALLOWED  
FOR SOME POCKETS OF FOG, LOCALLY DENSE AT TIMES.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 400 AM EDT FRI JUL 21 2017  
 
COMPLEX NEAR TERM AS 2 CLUSTERS OF STORMS TO MONITOR, FIRST ONE  
TAKING AIM AT SW PARTS OF THE AREA OVER THE NEXT COUPLE OF HOURS  
AND SECOND ONE UPSTREAM IN EASTERN IOWA. PAST FEW RUNS OF HRRR HAS  
INITIALIZED FAIRLY DECENT IN HANDLING OF BOTH AREAS OF CONVECTION  
WITH EVEN SOME INDICATIONS OF UPTICK IN INTENSITY/COVERAGE AS THE  
FIRST AREA MOVES INTO THE WESTERN CWA. SOME CONCERN THAT THIS  
AREA COULD BECOME SOMEWHAT MORE ORGANIZED AS IT RIDES GRADIENT OF  
2000 J/KG OF SBCAPE AND MID LEVEL LAPSE RATES OVER 7 C/KM. IR  
CLOUD TOPS HAVE BEEN ALSO COOLING WITH OVERALL LOOKS OF A BOWING  
SEGMENT TRYING TO TAKE SHAPE. UPDATED GRIDS EARLIER TO NUDGE POPS  
UP HIGHER AND SOMEWHAT FURTHER NORTH TO HANDLE NORTHWARD  
PROPAGATION OF INITIAL CELLS. THINKING LOCATIONS FROM LAPORTE  
COUNTY SOUTH AND EAST INTO GRANT COUNTY HAVE THE BEST SHOT OF  
SEEING SOME MEASURABLE RAINFALL AND STORMS THROUGH 12Z WITH A SLOW  
WEAKENING TREND THEREAFTER. 25 TO 30 KT LOW LEVEL JET APPEARS TO  
BE FEEDING INTO BACK OF THE FIRST LINE, KEEPING MOISTURE FEED  
INTACT AND AIDING SOMEWHAT IN INCREASED FORWARD MOVEMENT. THREAT  
OF LOCALLY GUSTY WINDS OR SMALL HAIL DOES EXIST, BUT GREATER  
CONCERN MAY BE RAINFALL WITH PWATS 2" OR SLIGHTLY MORE.  
INTRODUCING AT LEAST A SMALL WINDOW OF CATEGORICAL POPS IN SW  
AREAS NEXT COUPLE OF HOURS AND MONITOR TRENDS.  
 
2ND COMPLEX/MCV APPEARS TO BE FOLLOWING RIGHT BEHIND THE FIRST ONE  
WITH A EAST TO SLIGHTLY SOUTHEAST TREND. NOT SURE HOW LONG IT WILL  
SURVIVE OR IMPACTS TO SW LOCATIONS SO WILL ALLOW POPS TO LINGER INTO  
MID MORNING BEFORE DRYING THINGS OUT AS BOUNDARY WILL LIKELY BE AT  
LEAST TEMPORARILY PUSHED SOUTH INTO CENTRAL INDIANA. HOW FAST THE  
BOUNDARY WORKS BACK NORTH AND IT'S IT MOVES BACK NORTH WILL DEPEND  
ON AMOUNT/TIMING OF CLEARING NORTH OF IT AND INCREASING LOW LEVEL  
FLOW WHICH MAY BE DELAYED UNTIL TONIGHT. NAM TAKES THE FRONT THE  
FURTHEST NORTH WELL INTO MICHIGAN, BUT IS DISCOUNTED AS IT HAS NO  
CLUE ON CURRENT CONVECTION AND THUS STARTS TOO FAR NORTH. FRONT WILL  
LIKELY RESIDE SOMEWHERE NEAR OR JUST INTO SOUTHERN COUNTIES TOWARDS  
00Z AND THEN TRY TO MOVE NORTHWARD AS COMPLEX OF STORMS TAKES SHAPE  
ACROSS THE EASTERN DAKOTAS/MINNESOTA AND EVENTUALLY DROPS SOUTHEAST.  
FRONTAL LOCATION WILL DICTATE TO SOME EXTENT HOW FAR SOUTH THIS WILL  
TRACK AND AS A RESULT NOT READY TO MAKE MAJOR CHANGES TO POPS  
OVERNIGHT. NOT A BIG FAN OF CATEGORICAL POPS IN FAR N AREAS LATER  
TONIGHT, BUT ENOUGH SIGNALS POINTS TOWARDS MAINTAINING IT, BUT NOT  
BRINGING ANY FURTHER SOUTH FOR THE MOMENT EVEN THOUGH COULD EASILY  
BE ARGUED FOR LOCATIONS NORTH OF ROUTE 30.  
 

 
   
LONG TERM
 
(SATURDAY THROUGH THURSDAY)  
ISSUED AT 400 AM EDT FRI JUL 21 2017  
 
FRONTAL BOUNDARY RESPONSIBLE FOR THE PERIODS OF ACTIVE WEATHER  
ACROSS THE REGION WILL FINALLY BE PUSHED SOUTH OF THE AREA BY SUNDAY  
AS UPPER LEVEL TROUGH BRIEFLY DIGS INTO THE GREAT LAKES. HOW MUCH  
CONVECTION MAY OCCUR WITH THE PASSAGE OF THE FRONT AND ARRIVAL OF  
THE WAVE REMAINS SOMEWHAT DEPENDENT ON EVOLUTION OF CONVECTION  
TONIGHT INTO SAT MORNING. FRONTAL TIMING LATE AFTERNOON INTO EVENING  
WOULD NORMALLY BE FAVORABLE, BUT AMOUNT OF HEATING AND SUBSEQUENT  
DESTABILIZATION WILL DEPEND ON TRACK/TIMING OF EXPECTED MCS TONIGHT.  
UPPER LEVEL WAVE WILL HAVE A BIT MORE PUNCH THAN RECENT ONES WHICH  
MAY HELP OVERCOME POTENTIAL IMPACTS OF CLOUDS. WILL MAINTAIN HIGHER  
POPS NORTH SAT AM FOR POTENTIAL IMPACTS OF OVERNIGHT MCS TRACKING  
ACROSS AT LEAST THE NORTHERN HALF OF THE AREA. BEYOND THAT CAN'T  
JUSTIFY ANYMORE THAN CHC POPS THIS FAR OUT WITH NO CONFIDENCE IN  
MODEL EVOLUTION.  
 
COOLER AND LESS HUMID AIR WILL START TO ARRIVE ON SUNDAY, WITH MAIN  
PUSH COMING SUN NIGHT INTO MONDAY WHEN TEMPERATURES DROP BELOW  
NORMAL. UPPER LEVEL FLOW QUICKLY FLATTENS OUT AND THEN BUILDS  
SLIGHTLY ALLOWING TEMPS TO HEAD BACK TOWARDS NORMAL LEVELS AGAIN.  
FORECAST SHOULD REMAIN DRY UNTIL LATE IN THE PERIOD WHEN NEXT WAVE  
RIPPLES THROUGH THE FLOW AND BRINGS AT LEAST A CHANCE FOR  
SHOWERS/STORMS BACK TO THE AREA.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)  
ISSUED AT 140 AM EDT FRI JUL 21 2017  
 
UPSTREAM CONVECTION HAS FIRED INTO NORTH CENTRAL IL AND WAS MOVING  
EAST AT ISSUANCE TIME. 04Z HRRR HAS SOMEWHAT OF A HANDLE ON THIS  
AND SLIDES IT EAST SOUTHEAST...JUST MISSING BOTH TERMINALS TO THE  
SOUTH. HAVE INCLUDED A VCTS FOR TIMING BUT ANY FURTHER NORTHWARD  
DEVELOPMENT COULD RESULT IN SOME THUNDER AT BOTH SITES TOWARD  
DAYBREAK AND JUST AFTER. EXPECT SUBSIDENCE BEHIND THIS WAVE TO  
LIMIT CONVECTION UNTIL LATER THIS AFTERNOON AND TONIGHT.  
HOWEVER...TIMING AND LOCATION MAKE CHANCES TOO SMALL TO INCLUDE IN  
POINT FORECASTS AT THIS TIME. BEST CHANCES LIKELY NEAR OR AFTER  
ENDING VALID PERIOD FOR THIS SET OF TAFS.  
 

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

 
 

 
 
UPDATE...FISHER  
SYNOPSIS...FISHER  
SHORT TERM...FISHER  
LONG TERM...FISHER  
AVIATION...LASHLEY  
 
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