IND issues Area Forecast Discussion (AFD) at Aug 16, 1:31 PM EDT
071
FXUS63 KIND 161731
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
131 PM EDT Sat Aug 16 2025
.KEY MESSAGES...
- Increasing chances for storms this weekend, especially along and
north of I-70. Isolated strong to severe storms with strong
winds are possible, along with locally heavy rain.
- Hot and humid conditions still expected this weekend, increased
storms may result in highs in the upper 80s and heat indices below
100.
- Greater threat for thunderstorms to develop Tuesday and Wednesday
ahead of a cold front with cooler and drier air expected by mid week.
&&
.FORECAST UPDATE...
Issued at 1005 AM EDT Sat Aug 16 2025
Following a morning lull in convection over central Indiana, new
development is now beginning to take shape north of the Kokomo
area...with at least isolated showers expected to follow over
northern portions of the CWA where skies have cleared. Potential
for marginally strong/severe cells is still on the table, especially
later today when instability will be noticeably greater. However,
expecting mediocre 500-700 mb lapse rates to mitigate severe threat
for most areas. Any marginally severe cells will be most likely
over west/northwest zones where 25-35KT bulk wind shear could
produce higher towers.
Still expecting highs in the low 90s for most areas today, although
convection timed to the early afternoon could hold a few areas to
the upper 80s. Humid conditions will be the rule with dewpoints
mainly 70-75 degrees...with resultant afternoon maximum heat indices
in the upper 90s to around 100 degrees.
&&
.SHORT TERM (Today and tonight)...
Issued at 302 AM EDT Sat Aug 16 2025
High uncertainty in convective development leads to a low confidence
forecast through the short term.
Early This Morning...
Convection across central Illinois had dissipated, but some isolated
storms have redeveloped on the north side of it. This convection
could survive into the northern forecast area before it weakens.
Will monitor and add some low PoPs as needed.
Additional convection had developed across northern Illinois, but
its propagation has been mainly east.
Patchy ground fog will continue, especially south and east which
will have less cloud cover from the upstream convection.
Today and Tonight...
An upper high will continue to the west of central Indiana, and
upper energy will move around this high and bring forcing at times
to the area through tonight.
Even with cloud cover at times from convection to the west,
instability will build today and persist into tonight (though
diurnally lower tonight). The upper energy should interact with this
instability and produce scattered convection at times.
Mesoscale influences, such as surface boundaries from older
convection, could potentially have big impacts as well, increasing
the uncertainty on the specifics.
Given the uncertainties, will keep PoPs no higher than chance
category for now, with later updates refining/increasing as
necessary. Based on the expected position of the upper high, the
best chances for convection will be over the northern and eastern
portions of the forecast area.
There is enough weak shear for the potential of some isolated strong
to severe convection, mainly this afternoon and evening when
instability is maximized. Damaging winds would be the primary
threat, along with locally heavy rain.
High temperatures today will depend on how convection develops. For
now, will continue to undercut guidance a bit in the northeast where
odds of convection are highest. Even so, highs will be from around
90 northeast to lower and middle 90s southwest. Heat indices around
100 are possible in the warmest areas. Lows tonight will be in the
lower 70s.
Even though today could be the start of a string of days with heat
indices around 100 degrees, will hold off on issuing a Heat Advisory
(for prolonged near criteria heat) given the uncertainties in
convection and related effects.
&&
.LONG TERM (Sunday through Friday)...
Issued at 302 AM EDT Sat Aug 16 2025
Sunday through Monday...
An upper ridge centered near the region will allow unseasonably hot
and humid conditions to persist into early next week. Highs in the
low-mid 90s combined with high humidity will lead to peak heat
indices reaching around 100-105 degrees each afternoon. However, a
complicated convective forecast limits confidence in these expected
heat indices being reached.
The reason for limited confidence is guidance suggest upstream storm
complexes will propagate towards the area within northwest flow
aloft. It is typical for models to struggle with these subtle
impulses riding along the northern periphery of ridges. That is
evident in the widely varying solutions from both high resolution
and global models. Will stick to low POPs at times from blended
guidance given the high uncertainty, primarily over N/NE counties on
Sunday. Organized severe weather is unlikely due to weak deep-layer
shear. That being said, isolated strong to severe storms cannot be
ruled out given strong instability and steep low-level lapse rates.
The primary threats from storms would be localized heavy rain or
isolated damaging wind gusts.
POPs were not added for Monday as guidance depicts the upper ridge
axis shifting eastward into Indiana which could promote stronger
subsidence. Some convection cannot be ruled out on Monday, but will
keep the forecast dry at this time. Rain chances will likely need to
be refined in future updates once guidance becomes better aligned.
Any convection or convective cloud debris could limit daytime
heating or peak heat indices.
Tuesday onward...
Upper troughing setting up over the region Tuesday and Wednesday
along with a cold front moving through will support better chances
for precipitation. Uncertainty in exact details remains due to
diverging model solutions though. The greatest chance for
thunderstorms appears to be late Tuesday when the strongest forcing
and deeper moisture align. By Wednesday, guidance generally suggest
the front will have pushed through much of the area. Low POPs remain
in the forecast though as lingering low-level moisture and forcing
for ascent could promote isolated to scattered convection.
Peak heat indices around 100-105 are still possible Tuesday ahead of
the cold front before cooler air filters in mid-late week. Highs in
the low-mid 90s Tuesday should fall into the 80s mid-late week along
with lower humidity. Surface high pressure building in late
week will support mostly dry conditions.
&&
.AVIATION (18Z TAF Issuance)...
Issued at 130 PM EDT Sat Aug 16 2025
Impacts:
- TSRA possible at times through Sunday afternoon, especially near
KIND/KLAF...yet high uncertainty in specifics
- Fog possible at KBMG tonight
Discussion:
Low confidence continues in TAFs given uncertainties in further
convective development today through Sunday. Broad outflow boundary
over northeastern central Indiana will promote convective initiation
this afternoon near the Indianapolis Metro, while greater wind shear
aloft will be near KLAF. Overall isolated/scattered convective SHRA
and TSRA are expected this afternoon into this evening...although
confidence remains low in specific timing or location under the
broad and weakly-forced upper ridge.
VFR conditions are expected outside of any convection. Winds today
and tonight away from any convection should be sustained mainly
under 7KT. Fog development is expected overnight, especially at
KBMG. A decaying complex of storms/showers may cross central
Indiana early Sunday...with light northwesterly breezes possible in
its wake, towards the end of the TAF period.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
UPDATE...AGM
SHORT TERM...50
LONG TERM...Melo
AVIATION...AGM
Source: IND issues Area Forecast Discussion (AFD) at Aug 16, 1:31 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202508161731-KIND-FXUS63-AFDIND)
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