381  
FXUS63 KIWX 201409  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
1009 AM EDT SUN MAY 20 2018  
   
SYNOPSIS
 
 
ISSUED AT 316 AM EDT SUN MAY 20 2018  
 
SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE INTO  
MONDAY AS A FRONTAL BOUNDARY REMAINS IN THE REGION. LOCALLY HEAVY  
RAIN IS POSSIBLE ALONG WITH A SMALL RISK OF STRONG STORMS SUNDAY  
AFTERNOON AND EVENING ALONG AND SOUTH OF ROUTE 24. DRY AND WARMER  
WEATHER RETURNS FOR THE MIDDLE OF THE WORK WEEK.  
 

 
   
UPDATE
 
 
ISSUED AT 1008 AM EDT SUN MAY 20 2018  
 
SOME CHANGES TO FORECAST MAY BE WARRANTED, ESPECIALLY ACROSS N/NW  
AREAS BASED ON RADAR AS WELL AS HRRR. 2 AREAS OF SHOWERS/EMBEDDED  
STORMS, 1 OVER N IL/S WI AND THE OTHER S IL WERE WORKING EAST.  
HRRR SUGGESTS THAT THESE 2 AREAS WILL COME TOGETHER AND AT LEAST  
ATTEMPT TO MOVE ACROSS THE FORECAST AREA, ALBEIT LIKELY IN A  
WEAKENING STATE AS LOSS OF LLJ OCCURS. CURRENT GRIDS HAVE SLGT CHC  
TO CHC POPS AND WILL LET THEM RIDE FOR THE NEXT HOUR OR SO TO  
MONITOR TRENDS.  
 
HRRR ALSO SUGGESTS THAT A SMALL CLUSTER OF STG-POSSIBLY SEVERE  
STORMS COULD DEVELOP SOUTH OF US-24 AND THEN PROPAGATE SE TOWARDS  
BETTER INSTABILITY. GIVEN REMNANTS OF ABOVE NOTED CONVECTION AND  
POSSIBLE MCV SCENARIO IS AT LEAST PLAUSIBLE. AGAIN PREVIOUS SHIFT  
HAD SOME LOW POPS WHICH WILL WORK FOR THE TIME BEING.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 316 AM EDT SUN MAY 20 2018  
 
SIZABLE UNCERTAINTY REMAINS IN THE FORECAST CONCERNING CONVECTIVE  
CHANCES LATER THIS MORNING AND TONIGHT. COMPLEXITY OF THE  
FORECAST STEMS FROM THE CONVECTIVE INFLUENCES OF ONGOING  
CONVECTION ACROSS THE CENTRAL US. CONVECTION OVER LOWER WI AND  
NORTHERN IL MAY BE ABLE TO SNEAK IN OUR NORTHERN ZONES TOWARDS  
DAYBREAK SINCE AS IT IS CLOSEST TO THE LIMITED UPPER LEVEL  
DYNAMICS. HAVE RETAINED LOW END POPS FOR THE MORNING HOURS MAINLY  
FOR THE NORTHWESTERN ZONES.  
 
WEAK UPPER LEVEL RIDGING SHOULD WIN OUT DURING THE DAY TO KEEP ANY  
CONVECTIVE ACTIVITY LIMITED TO A FEW ISOLATED SHOWERS. AS WE MOVE  
INTO THE EARLY AFTERNOON HOURS, THE SHORTWAVE WHICH INITIATED  
STORMS ACROSS THE SOUTHERN GREAT PLAINS OVERNIGHT WILL BE NEARING  
THE AREA. THIS SHOULD BE ENOUGH TO INITIATE CONVECTION ALONG  
I-70. THERE IS GREAT UNCERTAINTY IF THIS CONVECTION WILL BE FAR  
ENOUGH NORTH FOR STRONG TO MARGINALLY SEVERE STORMS TO IMPACT THE  
AREA. IF THE CONVECTION DEVELOPS FURTHER NORTH (POSSIBLY ALONG  
ROUTE 24) THAN WHERE CAMS ARE CURRENTLY SHOWING THEM, THEN WE  
COULD SEE ORGANIZED STORMS. BUT IF THE CAMS ARE CORRECT WITH THE  
FURTHER SOUTH POSITIONING (ALONG I-70) THEN THE AREA WOULD BE  
STUCK UNDERNEATH THE RAIN SHIELD.  
 

 
   
LONG TERM
 
(MONDAY THROUGH SATURDAY)  
ISSUED AT 316 AM EDT SUN MAY 20 2018  
 
STORMS ARE STILL EXPECTED FOR THE START OF THE WORK WEEK. SOME  
LINGERING STORMS FROM THE PREVIOUS NIGHT ARE POSSIBLE MONDAY  
MORNING. MODELS SHOW A SLIGHT LULL IN ACTIVITY AROUND MIDDAY  
BEFORE THE NEXT ROUND OF STORMS DEVELOP DURING THE LATE  
EVENING/OVERNIGHT HOURS. THE SECOND ROUND OF STORMS COULD HAVE  
THE ABILITY TO BECOME ORGANIZED WITH 1000 - 1500 J/KG OF MLCAPE  
AND DEEP LAYER SHEAR OF 40KT. THE BEST CHANCE FOR ORGANIZED  
CONVECTION IS THE SOUTHERN COUNTIES OF THE CWA (PRIMARILY ALONG  
AND SOUTH OF ROUTE 24). AS TIME PROGRESSES, SURFACE WIND FLOW  
BECOMES VERY WEAK AND THUS STORMS WILL BECOME COLD POOL DOMINATED  
AS THEY LIFT NORTHEAST. EARLY ON BOTH HAIL AND DAMAGING WIND GUSTS  
WOULD BE THE PRIMARY HAZARDS, BUT DAMAGING WIND GUSTS WOULD BE  
THE PRIMARY HAZARD LATER IN THE NIGHT. PWATS REMAIN IN THE 1.5"  
RANGE THROUGHOUT THIS ROUND OF CONVECTION KEEP THE POSSIBILITY OF  
PERIOD OF MODERATE TO HEAVY RAINFALL.  
 
A FEW LINGERING STORMS ACROSS WESTERN OHIO SHOULD CLEAR OUT  
DURING THE EARLY PARTS OF THE DAY ON TUESDAY. THIS WILL START OUR  
DRY PERIOD WHICH IS EXPECTED TO LAST INTO THE LATTER PARTS OF THE  
WORK WEEK. OUR NEXT CHANCE OF STORMS ARE ON THE HORIZON AT THE END  
OF THIS FORECAST CYCLE (FRIDAY/SATURDAY).  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 639 AM EDT SUN MAY 20 2018  
 
LIGHT NORTH TO NORTHEAST FLOW CONTINUED OVER NORTHERN INDIANA ON  
THE NORTH SIDE OF A STATIONARY FRONT. WIDESPREAD POSTFRONTAL  
CONDITIONS HAVE BECOME IFR OVER FAR SOUTHERN LOWER MICHIGAN INTO  
NORTHERN INDIANA. GIVEN THE LATEST OBS & TRENDS COMBINED WITH  
CONDITIONAL CLIMATOLOGY, HAVE DELAYED IMPROVEMENT OF IFR  
CONDITIONS AT THE TERMINALS. MUCH UNCERTAINTY CONCERNING THE  
TIMING AND DEVELOPMENT OF CONVECTION THIS AFTERNOON AND EVENING.  
FOR NOW, HAVE MENTION OF THUNDER AFTER 00Z, BUT THIS TIMING MAY  
NEED TO BE ADJUSTED. THERE IS A GOOD CHANCE AN EXPANDING MESO  
CONVECTIVE COMPLEX NEAR ST. LOUIS EARLY THIS MORNING WILL BRING  
SHOWERS AND STORMS INTO NORTHERN INDIANA.  
 

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

 
 

 
 
UPDATE...FISHER  
SYNOPSIS...CM  
SHORT TERM...CM  
LONG TERM...CM  
AVIATION...SKIPPER  
 
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