428
FXUS63 KIWX 150933
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
533 AM EDT FRI AUG 15 2025
KEY MESSAGES
- HOT THIS WEEKEND WITH HIGHS IN THE UPPER 80S AND LOW 90S. HEAT
INDICES WILL CLIMB TO AROUND 100 DEGREES. SLIGHTLY COOLER NEXT
WEEK.
- CHANCES FOR SHOWERS AND THUNDERSTORMS THIS WEEKEND (20-40%),
WITH A MARGINAL RISK FOR STRONG-SEVERE STORMS ON SATURDAY
AFTERNOON. THE PRIMARY THREAT WITH THE STRONGEST STORMS WILL
BE DAMAGING WINDS.
- CHANCES (20-45%) FOR SHOWERS AND STORMS PERSIST THROUGH
WEDNESDAY, THEN BECOMING DRY NEXT THURSDAY AND FRIDAY.
DISCUSSION
ISSUED AT 533 AM EDT FRI AUG 15 2025
DRY CONDITIONS ARE EXPECTED TODAY AND TONIGHT WITH HIGH PRESSURE AT
THE SURFACE AND AN UPPER RIDGE BUILDING IN ALOFT THROUGH THE DAY (SW
TO NE). THIS WILL PLACE OUR CWA ON THE PERIPHERY OF THE RIDGE,
SUSCEPTIBLE TO ANY SHORTWAVES RIPPLING THROUGH THE FLOW.
THE FIRST WAVE ARRIVES SATURDAY, WITH VARIABLE TIMING AND STRENGTH
PREDICTED AMONGST THE MODELS. SPC HAS OUR NORTHWESTERN CWA IN A
MARGINAL RISK FOR STRONG TO SEVERE STORMS IF ANY STORMS MANAGE TO
DEVELOP AT ALL (LOW CONFIDENCE). RIGHT NOW HAVE BROAD LOW CHANCES OF
ABOUT 20% THROUGH THE EVENING, WITH THE BEST POTENTIAL FOR STRONG-
SEVERE STORMS IN THE AFTERNOON WHEN WE HAVE AROUND 1500-2500 J/KG OF
SFC BASED CAPE AND POTENTIALLY AS MUCH AS 20-40 KNOTS OF 0-6 KM BULK
SHEAR (VARIABLE MODEL GUIDANCE ON THAT). MID LEVEL LAPSE RATES ALSO
VARY A BIT BETWEEN MODELS-LIKELY IN THE 6-7 C/KM RANGE. THE MOST
LIKELY THREATS WILL BE DAMAGING WIND, HEAVY RAIN, AND LIGHTNING IN
THE STRONGEST STORMS IF THEY MATERIALIZE. SOME OF THE GUIDANCE BRING
AN MCS FROM WI INTO OUR CWA SATURDAY MORNING, WHICH WILL IMPACT THE
INSTABILITY FOR THE AFTERNOON (AND THE REASON I LEFT 20% CHANCE IN
DURING THE MORNING HOURS). OTHERS REMAIN DRY UNTIL THE AFTERNOON OR
SHOW ANY INCOMING SYSTEM DECAYING SIGNIFICANTLY BEYOND THE LAKE MI.
THE ECMWF HAS US COMPLETELY DRY UNTIL AFTER 21Z, THE GFS BRINGS IT
IN BY 18Z IN THE NORTHWEST. THE MORE AGGRESSIVE NAM SOLUTION BRINGS
THE MCS INTO OUR WEST BY 12-15Z, THEN SUSTAINS IT AS IT MOVES EAST-
SOUTHEAST THROUGH THE AFTERNOON. IN TERMS OF THE HIGH-RES
MODELS...WE SEE EVEN GREATER DIFFERENCES. THE RAP IS SIMILAR TO THE
NAM IN TERMS OF A 15-16Z ENTRY IN THE NORTHWEST, THEN CARRIES AT IT
MORE SOUTH-SOUTHEAST AS IT DRAMATICALLY DECAYS. THE HRRR HAS
ISOLATED-SCATTERED SHOWERS/STORMS DEVELOPING MORE NORTH-NORTH
CENTRAL TOWARDS THE LATE MORNING/EARLY AFTERNOON-AND DOESN'T EVEN
BRING IN A FULL MCS AT ALL. FV3 IS A MIX BETWEEN THE NAM/RAP.
A SECONDARY WAVE WILL MOVE IN OVERNIGHT, WITH THE NAM/GFS/ECMWF
BRINGING IN STRONGER MID-LEVEL LAPSE RATES OF 6.5 TO EVEN 8C/KM (NAM
WORST), BUT MODELS DISAGREE AS TO HOW FAR SOUTH THE SYSTEM WILL
REACH (OR IF IT WILL CONTINUE MORE NORTH/EAST IF THE RIDGE CONTINUES
TO BUILD. MOISTURE TRANSPORT IS QUESTIONABLE/WEAKER THROUGH THIS
PERIOD, SO THIS IN COMBINATION WITH WANING INSTABILITY COULD LIMIT
THE SEVERITY OF ANY STORMS THROUGH THE MORNING HOURS.
CHANCES FOR SHOWERS/STORMS IN THE 20-45% RANGE PERSIST MONDAY INTO
WEDNESDAY AS WE CONTINUE THE PATTERN OF SYSTEMS MOVING ALONG THE
RIDGE PERIPHERY. TUESDAY INTO WEDNESDAY THE RIDGE BREAKS DOWN AS A
STRONGER TROUGH MOVES THROUGH TO THE NORTHEAST (WITH THE TROPICAL
STORM/POTENTIAL HURRICANE ERIN MOVING ALONG THE EASTERN SEABOARD
LIKELY INFLUENCING MODEL OUTPUT AT THIS RANGE). ONCE WE GET INTO
THU/FRI, THE RIDGE STRENGTHENS AGAIN AND WE END UP DRY.
REGARDING HEAT, THE HOTTEST CONDITIONS LOOK TO BE SATURDAY AND
SUNDAY, WITH HIGHS IN THE UPPER 80S, LOW 90S EXPECTED. HEAT INDICES
WILL LIKELY HOVER AROUND 100 DEGREES, WITH POTENTIAL ADVISORIES
NEEDED. AT THIS POINT, HOWEVER, THERE IS UNCERTAINTY AS TO HOW HOT
IT WILL GET BECAUSE OF THE POTENTIAL FOR THE CLOUDS/PRECIPITATION TO
MOVE IN (ESPECIALLY IF IT IS ON THE CLOUDIER/RAINIER SIDE ON
SATURDAY MORNING). THE RIDGE WILL BEGIN TO WEAKEN THROUGH THE WEEK,
SO MON/TUE WILL BE IN THE MID-UPPER 80S, LOW 90S AND THEN WED-FRI
WILL BE IN THE LOW TO MID 80S.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 116 AM EDT FRI AUG 15 2025
AN UPPER LEVEL RIDGE WILL BUILD NORTHEAST INTO THE OHIO VALLEY AND
MIDWEST. VERY WEAK ENERGY MAY BE ABLE TO TOP THE RIDGE, BUT
GIVEN THE VERY STABLE CONDITIONS, ONLY AN ISOLATED SHOWER OR
STORM IS EXPECTED FRIDAY AFTERNOON. HAVE KEPT SHOWERS AND STORMS
OUT OF TAFS. PATCHY GROUND FOG IS POSSIBLE IN THE 1130Z TO
1330Z WINDOW, BUT HAVE ALSO KEPT FOG OUT OF TAFS GIVEN
UNCERTAINTY WITH DRIER AIR. WINDS SHOULD REMAIN UNDER 10 KNOTS
GIVEN THE WEAK SURFACE FLOW.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...NONE.
DISCUSSION...MCD
AVIATION...MCD
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