IND issues Area Forecast Discussion (AFD) at Aug 17, 1:32 AM EDT
866
FXUS63 KIND 170532
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
132 AM EDT Sun Aug 17 2025
.KEY MESSAGES...
- Scattered storms overnight
- Hot and humid conditions continue through Tuesday, cooler
afterwards
- Additional showers and storms likely during a frontal passage
Tuesday into Wednesday
&&
.FORECAST UPDATE...
Issued at 906 PM EDT Sat Aug 16 2025
Surface analysis this evening shows strong high pressure in place
over the northern plains, influencing the weather east into the
Great Lakes and Indiana. Aloft, a short wave was pushing across WI
and MI, helping to trigger storms. Meanwhile at the surface a very
warm and humid air mass remained in place across Central Indiana.
These features along with diurnal heating has resulted in
thunderstorm development, mainly within the Wabash Valley.
All afternoon and evening storms that have developed have shown
short lived sustainability as cold pools quickly become
dominate...choking updrafts and leading to an eventual dissipation
of the storm.
Earlier HRRR run suggesting an overnight MCS as backed off that
solution and given the convection across northern Indiana and NW
Indiana diurnal instability across those locations will be
considerably less. Thus continued convection, slowly diminishing, is
expected for the next 1-3 hours downstream of the current storms. In
the meantime storms may be capable of gusty winds due to a
downdraft, but widespread severe weather is not expected. Will use
high pops for the next few hours, trending toward low chc pops
overnight to account for the stray, renegade shower or storms due to
the very warm and moist airmass.
As dew point depressions once again fall to 1-3F, patchy fog,
particularly in rural areas will be possible.
Look for overnight low temperatures in the upper 60s and lower 70s.
&&
.MESOSCALE UPDATE...
Issued at 131 AM EDT Sun Aug 17 2025
Focus is currently on the southwestern forecast area early this
morning. This is the only area left that has not been worked over by
convection/outflow boundaries, and thus still has good instability
left.
An outflow boundary will create scattered convection across the far
southwest, while thunderstorms northwest of Terre Haute continue to
push slowly south and southeast.
While cloud tops have been warming for the most part, increases in
intensity are still possible given the existing instability (this
happened in the Bedford area earlier). Damaging winds and heavy rain
will be the primary threats with these storms.
&&
.SHORT TERM (This evening through Sunday)...
Issued at 235 PM EDT Sat Aug 16 2025
Rest of Today and Tonight.
For the latest on the ongoing convection and thoughts through the
evening, see the mesoscale discussion above.
As the diurnally driven convection gradually comes to an end this
evening, focus shifts to tracking a likely MCS across Wisconsin with
good model agreement in a southerly progression through the
overnight hours. There are some differences in the timing and
strength of this gradually decaying MCS, but the WRF-ARW which
typically handles organized convection better brings in the storms
towards 6-9Z which lines up well with the NAM and is a bit faster
than the HRRR.
This MCS should have a well-defined cold pool which will allow it to
progress into Indiana while maintaining at least some threat for
damaging winds with 1000-1500 J/kg of CAPE. The lack of shear will
be made up by the strength of the cold pool but do expect a general
downward trend as it moves southward. Overnight lows will remain
mild again tonight with most spots generally falling into the low
70s.
Sunday.
Generally warm and dry conditions are expected for Sunday with some
delay in the better heating as cloud cover from the dissipated MCS
takes time to clear. This MCS should progress south of the forecast
area but if it stalls and completely dissipates there could be an
initiation point along the outflow boundary and associated
differential heating boundary. Otherwise, chances for convection
look low with only an isolated shower or storm possible during the
afternoon and evening during peak heating. As a result of the
morning clouds, daytime highs are trending lower for Sunday with
increasing confidence that highs remain sub-90 with some spots
potentially struggling to rise out of the mid 80s depending on the
thickness and longevity of the cloud cover.
&&
.LONG TERM (Sunday night through Saturday)...
Issued at 235 PM EDT Sat Aug 16 2025
Sunday Night Through Tuesday.
Quiet weather is expected to continue into Sunday night with broad
ridging continuing to dominate the weather pattern. There will be
slight northerly component to the surface winds which will allow for
some drier air to slowly work into the area, but still expect to see
dew points in the upper 60s to low 70s towards daybreak. Stronger
southerly flow returns Monday into Tuesday ahead of a frontal
passage Tuesday night into early Wednesday.
Models are all over the place on the timing of the front and the
associated weather with the passage, but generally expect to see
showers and thunderstorms ahead of the front with a low-end
potential for more organized and strong to severe convection. With
weak shear and only modest instability, organized convection
potential looks low but will need to be monitored in the days ahead.
Wednesday Through Saturday.
Cooler weather is expected in the aftermath of the frontal passage
with daytime highs in the low 80s and overnight lows in the low to
mid 60s through the remainder of the workweek. Dry air both near the
surface and aloft should keep any precipitation chances minimal, but
there does look to be a more organized and stronger upper level low
across southern Canada Saturday into Sunday which could bring
additional showers and storms for the second half of the weekend
into next week. Looking beyond into the following workweek,
conditions look to favor cooler than normal weather to finish the
month.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 131 AM EDT Sun Aug 17 2025
Impacts:
- Convection at KHUF early in the period
- Additional convection is possible Saturday morning, but for now
feel these will remain east of the sites
- Isolated afternoon convection possible
- Fog possible before sunrise, mainly at KHUF/KBMG
Discussion:
Lower confidence TAFs continue as convection and effects from
previous convection continue to evolve.
Initial convection will be at KHUF. Convection currently across
northern Indiana/Illinois looks to remain east of the TAF sites as
they move southeast.
Isolated storms may pop up again this afternoon as mid and upper
clouds thin, allowing some instability to build. However, coverage
looks to be too low to mention in the TAFs at this time.
Winds will be variable through much of the period, but some trends
to the northwest will occur during the day.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
MESOSCALE...50
UPDATE...Puma
SHORT TERM...White
LONG TERM...White
AVIATION...50
Source: IND issues Area Forecast Discussion (AFD) at Aug 17, 1:32 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202508170532-KIND-FXUS63-AFDIND)
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