239
FXUS63 KIWX 200825 CCA
AFDIWX
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE NORTHERN INDIANA
425 AM EDT SUN JUL 20 2025
KEY MESSAGES
- AN AREA OF SHOWERS AND THUNDERSTORMS MAY IMPACT LOCATIONS
ALONG AND SOUTH OF US-30 BETWEEN 10 AM AND 2 PM EDT. HEAVY
RAINFALL, PONDING OF WATER AND LOCALLY GUSTY WINDS ARE THE
MAIN THREAT.
- SHOWER AND THUNDERSTORM CHANCES LINGER TONIGHT INTO EARLY
MONDAY MAINLY NEAR AND SOUTH OF US-24 IN INDIANA.
- HOT AND HUMID CONDITIONS REMAIN ON TRACK FOR WEDNESDAY AND
THURSDAY WITH HEAT INDICES NEAR OR ABOVE 100 DEGREES.
- THERE IS A MODERATE SWIM RISK FOR THE SOUTHEASTERN LAKE MICHIGAN
BEACHES IN LA PORTE AND SOUTHERN BERRIEN COUNTY FOR TODAY.
DISCUSSION
ISSUED AT 345 AM EDT SUN JUL 20 2025
WHILE SIGNALS ARE STRONG IN THE MODELS FOR AT LEAST 2 COMPLEXES
OF STORMS OVER THE NEXT 24 TO 36 HOURS ALONG AND NORTH OF A
QUASI-STATIONARY BOUNDARY, FINER MESOSCALE DETAILS REMAIN
PROBLEMATIC WITH REGARDS TO THE TRACK OF THESE SYSTEMS AND
IMPACTS. OUR FIRST COMPLEX IS RAPIDLY EXPANDING ACROSS SE IOWA
INTO WEST CENTRAL IL. HRRR HAS BEEN FAIRLY CONSISTENT ON THE
EXPANSION OF THIS AREA AS IT TRACKS EAST. WHILE FAIRLY HIGH
CONFIDENCE EXISTS ON IT MOVING INTO EASTERN IL, THE 850-300 MB
FLOW AND LOCATION OF THE THETA-E GRADIENT SUGGEST AT SOME POINT
THE STRONGEST PORTION OF THE COMPLEX WILL BEGIN AN SE TURN IN
THE 12-15Z WINDOW. HAVE MADE SOME MINOR TIMING/POP CHANGES
THROUGH 18Z TO ACCOUNT FOR A SLIGHTLY MORE NORTHWARD TREND ON
THE LIKELY POPS WHILE TRIMMING THE NORTHERN EXTENT OF ANY POPS
AS YOU HEAD INTO MI. WAS TEMPTED TO INCREASE TO CATEGORICAL
ALONG AND SOUTH OF US-24 WHERE GREATEST CHANCE FOR
SHOWERS/STORMS EXISTS, BUT GIVEN NOTED CONCERNS HELD WITH
LIKELY. MAIN CONCERN WILL HEAVY RAIN AS A VERY SOUPY ATMOSPHERE
WILL BE IN PLACE WITH A SWATH OF 0.5-1" OF RAIN IS LIKELY ON THE
US-24 CORRIDOR WITH HIGHER AMOUNTS IN SOME LOCATIONS. NEIGHBORS
TO THE SOUTH HAVE HOISTED FLOOD WATCHES GIVEN RECENT RAINFALL
AND HIGHER LIKIHOOD OF EVEN HEAVIER RAIN AMOUNTS. FOR US, THE
HEAVIEST RAIN THE PAST 24 HOURS FELL WELL NORTH OF THE
ANTICIPATED STORM TRACK TODAY. IN ADDITION, THE COMPLEX SHOULD
REMAIN PROGRESSIVE.
CONFIDENCE DECREASES THIS AFTERNOON AND INTO TONIGHT AS FINAL
TRACK OF THIS COMPLEX WILL GREATLY DETERMINE WHAT, IF ANY,
ADDITIONAL CONVECTION CHANCES EXIST. 06Z HRRR SEEMS TO PAINT A
VERY PLAUSIBLE SCENARIO WITH LITTLE/NO STORMS IN OUR SOUTHERN
AREA FROM MID AFTERNOON INTO EARLY MONDAY IN THE POST MCS
SUBSIDENCE AREA. CONFIDENCE WAS NOT HIGH ENOUGH IN THIS SETUP TO
REMOVE THE LIKELY POPS THROUGH EARLY MONDAY, SO HAVE LEFT THEM
ALONE WITH THE DAY SHIFT IN A BETTER POSITION TO SEE HOW THE
TRENDS LOOK.
UPPER LEVEL RIDGING WILL BEGIN TO INCREASE LATE MONDAY INTO MID
WEEK, FINALLY ENDING THE TRAIN OF CONVECTIVE SYSTEMS, BUT ALSO
USHERING IN A RETURN TO HOT AND HUMID CONDITIONS. NO CHANGES
MADE TO LATER PERIODS AS SIGNALS REMAINING CONSISTENT ON
WEDNESDAY AND THURSDAY BEING THE WARMEST DAYS (HIGHS NEAR OR
ABOVE 90) AND HEAT INDICES NEAR OR ABOVE 100 DEGREES (HIGHEST
THURSDAY). BY NEXT WEEKEND, THE HEAT DOME WILL LIKELY HAVE
SHIFTED EAST ENOUGH TO END THE HEAT IMPACTS AND ALSO BEGIN TO
ALLOW AT LEASE SOME CHANCES FOR SHOWERS AND STORMS TO RETURN.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 153 AM EDT SUN JUL 20 2025
VFR CONDITIONS AS OF THIS WRITING AT BOTH TERMINALS, THOUGH
EXPECT A DETERIORATION TO MVFR AND POSSIBLY IFR VISIBILITIES AS
WE HEAD INTO THE MORNING HOURS. STARTED TEMPO GROUPS AT 8-9Z FOR
MVFR CEILINGS BETWEEN 1500-2500 FT, BEGINNING AT KSBN AS THE
COLD FRONT SINKING SOUTHWARD FROM WI/CENTRAL AND NORTHERN LOWER
MI REACHES FAR NORTHERN IN/SOUTHERN MI. IT'S UNCERTAIN EXACTLY
WHERE THE FRONT WILL STALL, BUT INCREASING MOISTURE TRANSPORT
WITH THE LLJ AHEAD OF THE FRONT TONIGHT (COMBINED WITH THE
RAINFALL FROM STORMS/SHOWERS EARLIER IN THE DAY) INCREASES MY
CONFIDENCE IN AT LEAST LOWER-END MVFR CEILINGS IF NOT IFR
CEILINGS AT BOTH SITES. AT THE MOMENT, CEILINGS ALONG AND AHEAD
OF THE FRONT TO THE NORTH ARE IN THE 600-700 FT RANGE. KEPT
CEILINGS LIMITED TO 700 FT AT BOTH SITES (THROUGH 16Z AT KSBN,
17Z AT KFWA) BUT IT'S POSSIBLE KSBN DROPS A LITTLE LOWER THAN
THAT. VISIBILITIES UPSTREAM ARE HIGHLY VARIABLE, WITH POCKETS OF
GROUND FOG WITH VISIBILITIES OF 1/2-1 SM IN PLACES, AND MOST
OTHERS IN THE 4-7SM RANGE. WE'VE SEEN OCCASIONAL DROPS AT KSBN
AND JUST NORTH/EAST OF KFWA OVER THE PAST COUPLE OF HOURS, AND
WOULDN'T BE SHOCKED TO SEE SIMILAR CONDITIONS DEVELOP AT THE
TERMINALS. WAS ON THE FENCE ABOUT INCLUDING A TEMPO AT KFWA
EARLIER THAN THE CURRENT 9Z TIME-WILL AMEND IF NEEDED. OTHERWISE
POSSIBLE RAINSHOWERS BETWEEN 12-16Z AT KSBN (MAYBE DRIZZLE), AND
BETWEEN 13-17Z AT KFWA. AFTER 18Z, CEILINGS IMPROVE BUT THERE IS
POTENTIAL FOR KFWA TO BE SWIPED BY THUNDERSTORMS THROUGH ABOUT
00Z-BUT MUCH OF GUIDANCE KEEPS THE COMPLEX SOUTH OF THE
TERMINAL. HAVE VCTS WITH PROB30 FOR THE POSSIBILITY AT THIS
POINT-WILL KNOW MORE FOR 12Z TAFS ONCE WE SEE HOW FAR THE
FRONTAL ZONE HAS MOVED ALONG.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...NONE.
DISCUSSION...FISHER
AVIATION...MCD
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