IWX issues Area Forecast Discussion (AFD) at Jul 1, 1:31 PM EDT
412
FXUS63 KIWX 011731
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
131 PM EDT Wed Jul 1 2026
.KEY MESSAGES...
- Extreme Heat Warning remains in effect area-wide through
Thursday evening. Daily highs in the 90s and heat indices
between 103 to 110 degrees are expected.
- Near record warm overnight lows in the mid 70s will offer little
to no relief from the heat at night.
- Heat indices may exceed 100 degrees again on Friday, but heat
indices will be dependent on extent of afternoon clouds and
any scattered showers and storms.
- Highs in the upper 80s to low 90s for the 4th of July with
scattered showers and thunderstorms expected (40-60%)
&&
.DISCUSSION...
Issued at 330 AM EDT Wed Jul 1 2026
Persistence forecast utilized for today with overall little movement
in mean position of mid/upper level ridging across the OH/TN
Valleys. As was the case yesterday some light shallow fog is
trying to develop this morning given excessive sfc/near sfc dew
points. Some patchy stratus is possible through daybreak, but
coverage is expected to be much more limited in comparison to
yesterday morning. Otherwise today, broad weak synoptic scale
subsidence and a very warm 850-700 mb layer should suppress any
convective development, with greater potential of showers and
thunderstorms expected in vicinity of a plume of much higher
low level theta-e air from southern Minnesota through northern
Lower Michigan. With good deal of insolation today and little
change in thermodynamics from yesterday, would expect another
afternoon of peak heat indices in the 103 to 110 degree range
and will be locally determined by extent of local mixing/dew
point trends. Near term forecast soundings do show another
afternoon of potentially mixing up to levels that would support
some 20 mph afternoon gusts, but would expect these gusts to
quickly diminish toward 00Z this evening. Little relief from the
extreme heat is expected tonight with another night of mins in
the mid-upper 70s given the very high moisture content airmass
in place.
The mid/upper level ridge axis is expected to exhibit some slight
eastward progression tonight with the more favorable short wave
track remaining from the Upper Midwest into the northern Great
Lakes. Convection and convective high cloud debris will likely
remain displaced northwest of the local area into tonight, with
another night of mainly clear skies.
The passage of these more pronounced mid level convectively enhanced
short waves just north of the local area could provide some slight
suppression to the mean ridging by Thursday, with slightly cooler
low level thermals by this time. This would be a very modest
moderation if at all however, with low level thermal progs still
supporting heat indices at least into the 100 to 105 degree range
once again Thursday afternoon. It is possible there could be just
enough ridge suppression by later Thursday night that some remnants
of upstream convection or outflow forced convection could clip
the southern Great Lakes, but confidence in this scenario is
quite low at this time and will depend on exactly how upstream
mid level synoptic impulses are modified by upstream convection.
By Friday, the 596 dm upper ridge should begin to move to the Mid
Atlantic region with greater potential of a more flattened upper
ridge across the southern Great Lakes. The extent of convective
influence on this suppression remains a low confidence item for this
forecast, which has a corresponding low confidence impact on high
temps for Friday. If showers/storms remain of lesser coverage for
Friday, it is certainly possible another day of heat indices
around 100 may be realized and may necessitate a temporal
extension of the Extreme Heat Warning into Friday eventually. In
addition to the potential of heat indices around 100, some
isolated severe potential may evolve during the afternoon
through early overnight hours as convective inhibition for sfc
based parcels will likely be largely eroded by this time. Deep
layer shear will likely be more marginal however, and the exact
magnitude of shear profiles will be dependent on existence of
any small scale convectively enhanced short waves with locally
stronger shear profiles.
A high CAPE/marginal shear profile setup does look to be maintained
this holiday weekend into early next week with a potential of
several weak mid/upper level short waves progressing through the
dampened central CONUS ridge. Strong/severe potential is difficult
to assess at this forecast distance given continued reliance on
convective enhancement to short waves for better shear profiles, but
have continued broadbrush low chance thunder PoPs through much of
the long term. Hot and humid conditions will persist through next
week although likely not at advisory levels.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 129 PM EDT Wed Jul 1 2026
The main weather phenomenon in control of our local weather is the
strong ridge across the southeastern US. Shortwaves attempt to
buckle it over the next couple of days, but it appears to hold stout
in the short term, keeping thunderstorm activity to the north today
and tonight. As such, VFR conditions look to continue. The one
fly in the ointment might be the haze/low fog possibility
returning again Thu AM. Afternoon mixing today into the LLJ
allows for 20 to 25 kt more frequently at SBN, but also possibly
at FWA. Winds stay generally out of the southwest through the
period.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Extreme Heat Warning until 8 PM EDT /7 PM CDT/ Thursday for
INZ005>009-012>015-017-018-020-022>027-032>034-103-104-
116-203-204-216.
OH...Extreme Heat Warning until 8 PM EDT Thursday for OHZ001-002-
004-005-015-016-024-025.
MI...Extreme Heat Warning until 8 PM EDT Thursday for MIZ078>081-
177-277.
MARINE...None.
&&
$$
DISCUSSION...Marsili
AVIATION...Roller
Source: IWX issues Area Forecast Discussion (AFD) at Jul 1, 1:31 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202607011731-KIWX-FXUS63-AFDIWX)
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