961  
FXUS63 KIWX 062303  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
703 PM EDT MON JUL 6 2015  
   
SYNOPSIS
 
 
ISSUED AT 703 PM EDT MON JUL 6 2015  
 
A COLD FRONT OVER THE UPPER MIDWEST AND PLAINS WILL MOVE EAST  
ACROSS OUR AREA OVERNIGHT INTO TUESDAY. SHOWERS AND A FEW  
THUNDERSTORMS ARE EXPECTED TO ACCOMPANY THE FRONT AS IT MOVES  
THROUGH THE AREA. LOWS TONIGHT WILL BE IN THE UPPER 60S AND LOWER  
70S WITH HIGHS TOMORROW REMAINING IN THE 70S BEHIND THE FRONT.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY)  
ISSUED AT 344 PM EDT MON JUL 6 2015  
 
CONSOLIDATING POSITIVELY-TILTED LONGWAVE TROUGH EXTENDING FROM  
HUDSON BAY CLOSED LOW CONTINUES TO SLOWLY PUSH EAST AND THE  
ASSOCIATED COLD FRONT IS THE MAIN FEATURE OF NOTE FOR THIS SHORT  
TERM FORECAST. BEST CVA FORCING PASSES WELL TO OUR NORTH BUT MODELS  
STILL INDICATE DECENT MIDLEVEL HEIGHT FALLS GENERATING A HEALTHY (BY  
JULY STANDARDS ANYWAY) STRIPE OF LOW LEVEL (925-850MB) CONVERGENCE  
AND FRONTOGENESIS...AIDED TO SOME DEGREE BY NORTHERN LAKES UPPER JET  
STREAK. THIS COMBINED WITH A STRONG...ALBEIT NARROW...SURGE OF DEEP  
TROPOSPHERIC MOISTURE JUST AHEAD OF THE FRONT WILL SET THE STAGE FOR  
NUMEROUS SHOWERS AND THUNDERSTORMS LATE TONIGHT INTO TOMORROW.  
 
LATEST REGIONAL SURFACE OBS SHOW ACTUAL SURFACE BOUNDARY STILL WELL  
UPSTREAM ACROSS CENTRAL IOWA AND WISCONSIN. THERE IS HOWEVER A LINE  
OF CONVECTION MOVING THROUGH THE CHICAGO AREA ASSOCIATED WITH  
PREFRONTAL COLD POOL/OUTFLOW FROM OLD REMNANT MCS THAT HI-  
RES/CONVECTION-ALLOWING MODELS HAVE STRUGGLED ALL DAY TO CAPTURE.  
THIS ACTIVITY WILL MAKE A RUN FOR OUR WESTERN COUNTIES THIS  
EVENING BUT SHOULD CONTINUE TO SLOWLY FIZZLE OUT AS IT SHIFTS  
EAST. CONVECTIVE LINE IS ALREADY LOOKING OUTFLOW DOMINANT AND VERY  
RAGGED PER LATEST KLOT RADAR IMAGERY AND CONTINUES TO MOVE WELL  
OUT AHEAD OF MAIN SYNOPTIC SUPPORT. 12Z KILX AND KDTX UPPER AIR  
SOUNDINGS ALSO SHOWED A VERY DRY AND CAPPED ENVIRONMENT THAT HAS  
BEEN SLOW TO DISLODGE DUE TO WESTWARD DISPLACEMENT OF BETTER LLJ  
AND MOISTURE FLUX CONVERGENCE. SPC/RAP MESOANALYSIS CONFIRM THIS  
WITH MUCH DRIER AND MORE STABLE CONDITIONS OVER LOWER MICHIGAN AND  
NORTHERN INDIANA. A FEW DECAYING SHOWERS/STORMS MAY SNEAK INTO OUR  
WESTERN ZONES THIS EVENING BUT STILL EXPECT MUCH BETTER CHANCES  
FOR RAIN TO HOLD OFF UNTIL AROUND MIDNIGHT TONIGHT.  
 
ONLY REAL CHANGE TO GOING FORECAST WAS TO BUMP UP TIMING A BIT BASED  
ON LATEST GUIDANCE AND UPSTREAM OBS. STILL THINK JUST LIKELY POPS  
APPROPRIATE FOR OUR CWA...GIVEN FRONTAL PASSAGE DURING DIURNAL  
INSTABILITY MINIMUM. SEVERAL HI-RES MODELS HAVE LITTLE MORE THAN SCT  
SHOWERS AND WITH A LACK OF SUBSTANTIAL FORCING ALOFT...NOT  
COMFORTABLE GOING CATEGORICAL. SEVERE WEATHER RISK IS VERY LOW BOTH  
TONIGHT AND TOMORROW. POOR DIURNAL TIMING AND PALTRY MIDLEVEL LAPSE  
RATES LIMIT AVAILABLE INSTABILITY AND DEEP LAYER SHEAR IS 15 KTS OR  
LESS AHEAD OF THE FRONT. SLIGHT CHANCE FOR AN ISOLATED STRONG STORM  
SOUTH OF US-24 TOMORROW GIVEN SLIGHTLY LATER FRONTAL PASSAGE BUT  
EVEN THEN...BETTER SBCAPE VALUES REMAIN CONFINED SOUTHEAST OF OUR  
CWA BORDER. BRIEF HEAVY RAIN POSSIBLE GIVEN PW VALUES AOA 2 INCHES  
IMMEDIATELY ALONG FRONT BUT LACK OF GOOD INSTABILITY AND STRONG  
FORCING SUGGEST ANY HEAVIER RAINFALL RATES/AMOUNTS WILL BE  
ISOLATED. NOT EXPECTING MANY FLOODING ISSUES THANKS TO RECENT  
STRETCH OF DRY WEATHER.  
 

 
   
LONG TERM
 
(TUESDAY NIGHT THROUGH MONDAY)  
ISSUED AT 344 PM EDT MON JUL 6 2015  
 
COLD FRONT SHOULD EITHER BE THROUGH THE FORECAST AREA OR CONFINED TO  
FAR S/SE SECTIONS AT THE START OF THE PERIOD. MAY BE A FEW LINGERING  
SHOWERS OR STORMS IN ITS WAKE BUT MAJORITY OF TUESDAY NIGHT INTO  
FIRST PART OF WEDNESDAY SHOULD BE DRY.  
 
WHILE 12Z GFS/ECMWF ARE SIMILAR IN DEPICTION OF SERIES OF UPPER  
LEVEL DISTURBANCES...SURFACE FEATURES VARY SOMEWHAT WITH ECMWF/09Z  
SREF/12Z NAM12 ALL SHOWING FURTHER NORTH TRACK WITH VARYING AMOUNTS  
OF QPF WEDS NGT INTO THURS AND ECMWF AGAIN THURS NGT INTO FRIDAY.  
WITH GROUND STILL VERY WET TO SATURATED HYDRO CONCERNS COULD QUICKLY  
MATERALIZE.  
 
SINCE ANY OF THE SOLUTIONS ARE PLAUSIBLE AND CONFIDENCE IN ANY ONE  
LOW (CONSIDERING HOW MODELS ARE HANDLING TODAY'S CONVECTION) NOT  
COMFORTABLE MAKING ANY MAJOR CHANGES. MESOSCALE INFLUENCES ARE  
LIKELY TO WRECK HAVOC ON THE FRONTAL POSITION AND POTENTIAL TRACKS  
OF ANY COMPLEXES...RESULTING IN LOW TO MODERATE CONFIDENCE OF  
ADDITIONAL RAINFALL BUT LOW CONFIDENCE ON WHERE IT OCCURS. HAVE  
BLENDED HALF PREVIOUS FORECAST AND HALF SUPERBLEND OF MODELS WHICH  
COMES UP WITH A COMPROMISE. TEMPERATURES SHOULD HOLD BELOW NORMAL  
INTO FRIDAY BUT LOW LEVEL FLOW WILL INCREASE AND ALLOW HIGHS TO  
CLIMB BACK NEAR OR SLIGHTLY ABOVE NORMAL LEVELS.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)  
ISSUED AT 659 PM EDT MON JUL 6 2015  
 
A BROKEN LINE OF DECAYING SHOWERS WERE MOVING TOWARD KSBN AT  
ISSUANCE TIME. INCLUDED A BRIEF TEMPO GROUP EARLY THIS EVENING  
GIVEN PROXIMITY. HOWEVER...THESE SHOULD CONTINUE TO DISSIPATE AS  
THEY MOVE AWAY FROM BETTER FORCING AND INSTABILITY. NEXT ROUND OF  
PCPN WILL COME OVERNIGHT AS MAIN FRONT AND FORCING ARRIVE. TSRA  
AHEAD OF THIS IN NORTHERN IL TO ALSO WEAKEN WITH LOSS OF DIURNAL  
HEATING AND LACK OF STRONG FORCING. KEPT SHRA GOING AT KSBN. PCPN  
TO REACH KFWA LATE TONIGHT WITH A SLIGHTLY BETTER CHANCE FOR A  
TSRA NEAR OR AFTER SUNRISE TUE. OTHERWISE SLOWLY DECREASING CLOUDS  
TUESDAY WITH NORTHWEST WINDS 10 TO 20 KNOTS.  
 

 
   
IWX WATCHES/WARNINGS/ADVISORIES
 
 
IN...BEACH HAZARDS STATEMENT FROM TUESDAY MORNING THROUGH TUESDAY  
EVENING FOR INZ003.  
 
MI...BEACH HAZARDS STATEMENT FROM TUESDAY MORNING THROUGH TUESDAY  
EVENING FOR MIZ077.  
 
OH...NONE.  
LM...SMALL CRAFT ADVISORY FROM 8 AM TUESDAY TO MIDNIGHT EDT TUESDAY  
NIGHT FOR LMZ043-046.  
 

 
 

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