921  
FXUS63 KIWX 201829  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
229 PM EDT THU JUL 20 2017  
   
SYNOPSIS
 
 
ISSUED AT 215 PM EDT THU JUL 20 2017  
 
HOT AND HUMID CONDITIONS WILL REMAIN THE STORY INTO FRIDAY WITH  
LOW CHANCES FOR A SHOWER OR THUNDERSTORM NEAR A FRONTAL BOUNDARY.  
HIGHS EACH DAY WILL RANGE FROM THE MID 80S TO NEAR 90 DEGREES,  
WITH LOWS TONIGHT NEAR 70 DEGREES. BETTER CHANCES FOR SHOWERS AND  
THUNDERSTORMS ARRIVE LATER FRIDAY INTO SATURDAY AS A DISTURBANCE  
MOVES THROUGH THE REGION. LOCALLY HEAVY RAINFALL AND STRONG TO  
SEVERE THUNDERSTORMS WILL BE POSSIBLE DURING THIS TIME. COOLER AND  
LESS HUMID CONDITIONS THEN RETURN SUNDAY INTO EARLY NEXT WEEK.  
 

 
   
UPDATE
 
 
ISSUED AT 215 PM EDT THU JUL 20 2017  
 
LOWERED THE TEMPERATURE FORECAST FOR THIS AFTERNOON, AS THE  
DECAYING MCS LARGELY LIMITED TEMPERATURE INCREASES TODAY. STILL  
THINK MANY LOCATIONS-ESPECIALLY THOSE IN THE SOUTHWEST WHERE CLOUD  
COVER IS BROKEN UP-COULD REACH INTO THE MID-UPPER 80'S BY LATE  
AFTERNOON. OTHERWISE, EXPECT HIGHS WHERE CLOUD COVER IS MORE  
EXPANSIVE TO STAY IN THE LOW 80'S. ALSO REMOVED PRECIPITATION  
CHANCES AS WE ARE UNDER DECENT SUBSIDENCE FROM THE DEPARTING WAVE.  
OVERNIGHT AS A BOUNDARY SINKS INTO OUR AREA WE COULD SEE  
ADDITIONAL DEVELOPMENT. SEVERE WEATHER IS NOT EXPECTED THROUGH THE  
AFTERNOON/EVENING.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH FRIDAY)  
ISSUED AT 215 PM EDT THU JUL 20 2017  
 
A COMPLICATED SHORT TERM FORECAST OVERALL-WITH MUCH OF THE  
FORECAST AREA BENEATH ZONAL FLOW ON THE PERIPHERY OF AN UPPER  
LEVEL RIDGE THROUGH THE PERIOD. THUS, WE WILL SEE PRECIPITATION  
CHANCES WITH ANY SHORTWAVES THAT RIPPLE THROUGH THE FLOW,  
ESPECIALLY GIVEN THE MOIST AIRMASS FORECAST TO BE IN PLACE. AT THE  
SURFACE, A STATIONARY FRONT CURRENTLY NORTH OF THE AREA WILL TAKE  
A DIVE SOUTHWARD EARLY THIS EVENING...WHERE IT WILL AGAIN STALL  
OUT OVER OUR CWA-AND LEAD TO PRECIPITATION/STORM CHANCES THROUGH  
SUNDAY AS THE VARIOUS WAVES ALOFT MOVE THROUGH.  
 
FOR THIS EVENING, THOUGH THERE MIGHT BE AN ISOLATED SHOWER/STORM  
ALONG THE BOUNDARY AS IT SINKS SOUTHWARD, THINKING THAT SUBSIDENCE  
BEHIND THE PASSING WAVE FROM THIS MORNINGS PRECIPITATION WILL LIMIT  
ANY REAL DEVELOPMENT THROUGH THE EVENING. AS A RESULT, HAVE THE  
BEST CHANCES FOR SHOWERS/STORMS SOUTH OF US 30 AFTER 3Z, WHICH IS  
WHEN WE HAVE INCREASED CONFLUENCE NEAR THE FRONTAL BOUNDARY. KEPT  
CHANCES LIMITED TO 20-30 PERCENT GIVEN MODEL DISAGREEMENT, AND  
WEAKER LIFT. WHILE THERE IS A THREAT OF HEAVY RAIN WITHIN ANY  
STORMS THAT DEVELOP, THE RISK FOR SEVERE WEATHER IS EXTREMELY LOW  
OVERNIGHT. IF ANY STRONG UPDRAFTS MANAGE TO DEVELOP WITHIN THE  
MOST UNSTABLE AREAS, THINK IT'S POSSIBLE TO SEE ISOLATED DAMAGING  
WINDS- BUT AGAIN- CONFIDENCE IN THIS OCCURRING IS LOW.  
 
FRIDAY IS ANOTHER COMPLICATED STORY. THERE MAY BE A FEW  
SCATTERED/ISOLATED SHOWERS ALONG THE BOUNDARY (SOUTH OF US 30) EARLY  
IN THE AM, BUT OTHERWISE EXPECT MOST OF THE FORECAST AREA TO BE DRY  
BEFORE THE NEXT SHORTWAVE APPROACHES. HIGHS WILL MAKE ANOTHER RUN UP  
TO THE 80'S AND LOW 90'S, PARTICULARLY IF CLOUD COVER IS LIMITED.  
HUMIDITY WILL CONTINUE YET AGAIN, SO THOSE PARTICIPATING IN OUTDOOR  
ACTIVITIES WILL NEED TO PLAN ACCORDINGLY FOR SWELTERING, MUGGY  
CONDITIONS. CHANCES FOR SHOWERS/STORMS APPROACH FROM THE WEST AND  
SOUTHWEST TOWARDS LATE AFTERNOON. SEVERE WEATHER IS NOT EXPECTED  
DURING THE DAY. SPC HAS OUR AREA IN A SLIGHT RISK FOR DAY 2, BUT  
THIS IS MAINLY DUE TO THE POTENTIAL INCOMING MCS FRIDAY EVENING,  
WHICH WILL BRING THE POTENTIAL FOR DAMAGING WINDS/HAIL.  
 

 
   
LONG TERM
 
(FRIDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 215 PM EDT THU JUL 20 2017  
 
SEVERAL CONCERNS THIS WEEKEND-INCLUDING HEAVY RAIN/FLOODING  
POTENTIAL, HEAT/HUMIDITY, AND SEVERE WX POTENTIAL. HOWEVER, THREATS  
ARE VERY CONDITIONAL. AS MENTIONED IN THE SHORT TERM DISCUSSION,  
PRECIPITATION CHANCES ARE FOCUSED AROUND THE BOUNDARY THAT SETTLES  
ACROSS OUR CWA, AND THE VARIOUS SHORTWAVES THAT MOVE THROUGH IN THE  
RELATIVELY ZONAL FLOW ALOFT. WE HAVE LOWER CONFIDENCE WITH  
REGARDS TO PRECIPITATION/STORM CHANCES IN THESE SITUATIONS GIVEN  
THAT EACH MCS THAT DEVELOPS IMPACTS THE PRECIPITATION/STORM  
CHANCES FOR THE NEXT SYSTEM-SO MINOR CHANGES CAN LEAD TO BIGGER  
ERRORS FURTHER OUT.  
 
THAT BEING SAID, MID-RANGE MODEL GUIDANCE SUGGESTS THAT A MORE  
POTENT SHORTWAVE AND ASSOCIATED SURFACE TROUGH WILL SHIFT THROUGH  
FRIDAY NIGHT INTO SATURDAY, AND THEN LINGER THROUGH SUNDAY. FROM  
THE 12Z MODEL RUNS, IT ALMOST LOOKS LIKE WE COULD SEE A REPEAT OF  
LAST NIGHT/TODAY ON FRIDAY NIGHT/SATURDAY, WITH CONVECTION ALONG  
THE STATIONARY FRONT IN OUR CWA AND ANOTHER MCS DEVELOPING OVER  
WI IN THE EVENING. THIS WILL SNEAK INTO OUR AREA AND BRING  
WIDESPREAD RAIN WITH EMBEDDED STORMS THROUGH SATURDAY  
MORNING/AFTERNOON. MOST OF THE MODELS KEEP THE PRECIPITATION  
FOCUSED NORTH OF US 30-WHICH IS WHAT OUR PREVIOUS FORECASTER HAD  
HIGHLIGHTED WITH LIKELY POPS. I KEPT THIS TREND IN THE LATEST  
FORECAST PACKAGE.  
 
SEVERE WEATHER-WISE, SPC HAS OUR AREA IN A SLIGHT RISK THROUGH  
SUNDAY MORNING GIVEN THE MOIST AIRMASS, SUFFICIENT INSTABILITY (UP  
TO 2K SFC BASED CAPE), AND WIND SHEAR RANGING FROM 20-40 KNOTS.  
ASSUMING THOSE VALUES ARE ACCURATE WE COULD SEE SOME STRONG TO  
SEVERE STORMS FRI NIGHT-SATURDAY-BUT GIVEN THE UNCERTAINTY OF THE  
OVERALL FORECAST PATTERN HAVE LOW CONFIDENCE. DESPITE THIS, IT  
WOULD BE WISE TO MAINTAIN SITUATIONAL AWARENESS THROUGH FRIDAY  
NIGHT INTO SUNDAY AS WE'LL BE WATCHING THE EVOLUTION OF THIS  
SYSTEM CLOSELY.  
 
CONFIDENCE IN ANY ONE MODEL SOLUTION GOES DOWN SUNDAY, AS THEY ARE  
IN GENERAL DISAGREEMENT AS TO HOW THINGS PLAY OUT. THINK THERE WILL  
BE A BREAK IN PRECIPITATION FROM THE OVERNIGHT SYSTEM BEFORE WE SEE  
SOME REDEVELOPMENT WHEN THE BETTER FORCING FROM THE COLD FRONT  
ARRIVES SUNDAY NIGHT.  
 
HIGH TEMPERATURES THROUGH THE WEEKEND WILL BE IN THE 80'S AND EVEN  
POSSIBLY LOW 90'S, AS 850 TEMPS LINGER AROUND 20-22C. WE'LL SEE  
CONTINUED THREATS FROM HEAT AND HUMIDITY DURING THIS TIME-BUT HOW  
HOT WE GET WILL DEPEND ON THE CLOUD COVER/PRECIPITATION EVOLUTION-  
WHICH IS UNCERTAIN.  
 
A FINAL CONCERN WILL BE HEAVY RAIN/FLOODING POTENTIAL FRIDAY NIGHT  
INTO SUNDAY, WITH PWATS OF GREATER THAN 2" (175-200% ABOVE NORMAL)  
AND WARM CLOUD DEPTHS FORECAST TO BE UPWARDS OF 12K FT. MOISTURE  
TRANSPORT IS MAXIMIZED INTO OUR AREA AT THIS TIME, AND GIVEN THE  
ANTECEDENT CONDITIONS-THINKING THIS COULD EXACERBATE PROBLEMS IN  
AREAS THAT HAVE ALREADY EXPERIENCED FLOODING. AGAIN-CERTAINTY IS LOW  
GIVEN WE ARE UNSURE ABOUT THE CONVECTIVE EVOLUTION BUT IT IS  
SOMETHING TO BE MINDFUL OF THIS WEEKEND.  
 
MONDAY AFTERNOON INTO THURSDAY WE SEE SOME RELIEF IN REGARDS TO  
PRECIPITATION CHANCES, WHICH WILL BE EVER DECREASING AS A REGION OF  
HIGH PRESSURE SINKS OVER OUR AREA. COOLER TEMPERATURES WILL COME  
WITH THIS, WITH HIGHS EXPECTED TO BE IN THE 70'S AND LOW 80'S. SOME  
ISOLATED CHANCES MONDAY AS THE WEEKEND SYSTEM EXITS OUT-BUT  
OTHERWISE FAIRLY QUIET.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)  
ISSUED AT 103 PM EDT THU JUL 20 2017  
 
SUBSIDENCE IN WAKE OF MCV SINKING EAST-SOUTHEAST INTO OHIO WILL  
PROVIDE MAINLY DRY/VFR CONDITIONS INTO THIS AFTERNOON AND EVENING.  
LIGHT WINDS AND AMPLE NEAR SURFACE MOISTURE MAY ALLOW SOME IFR TO  
MVFR STRATUS/FOG TO SETTLE IN LATER TONIGHT, BEST CHANCES AT KFWA  
CLOSER TO COMPOSITE OUTFLOW. ANY CONVECTION ALONG THIS COMPOSITE  
OUTFLOW SHOULD MAINLY REMAIN SOUTH OF THE TERMINALS THROUGH THE  
TAF CYCLE.  
 

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

 
 

 
 
UPDATE...MCD  
SYNOPSIS...STEINWEDEL  
SHORT TERM...MCD  
LONG TERM...MCD  
AVIATION...STEINWEDEL  
 
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