172
FXUS63 KIND 182338
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
738 PM EDT Fri Jul 18 2025

.KEY MESSAGES...

- Showers with an isolated storm possible overnight.

- Strong to severe storms Saturday, including the potential for
flooding. The heavy rain and localized flood threat will persist
through the weekend into early next week.

- Likely hazardous heat conditions towards next Tuesday and beyond
  with peak heat indices potentially well into the 100s

&&

.SHORT TERM (This evening through Saturday)...
Issued at 244 PM EDT Fri Jul 18 2025

Surface analysis early this afternoon shows strong high pressure in
place over the Great Lakes. A poorly defined frontal boundary was
lingering near the Ohio River. This was resulting in a cooler
northeasterly flow of air across Central Indiana. Dew points
remained humid, holding in the middle to upper 60s. GOES16 shows
lower clouds scattering out over Central Indiana as heating and
mixing is prevalent. Water vapor shows a nearly zonal flow in place
across Indiana, with subsidence in place across WI and MI, which was
drifting east.

Tonight...

Quiet weather is expected to persist this evening before a more
active period of weather begins overnight. Our weather this evening
will continue to be dominated by the departing high pressure system
to the north, allowing subsidence along with northeasterly surface
winds.  Forecast soundings through the evening suggest a dry column.
Thus a pleasant but humid evening is expected.

Overnight the zonal flow aloft will persist and as the high drifts
farther east, lower level flow is expected to become more
southwesterly. This will allow the warm front lingering near the
Ohio river to drift northward and slowly cross Indiana. The GFS
310K isentropic surface shows a bit of lift with this feature
overnight and forecast soundings become much more moist as
subsidence is lost and weak lift arrives with the front. HRRR
suggests the development of an area of showers overnight with these
features pushing northeast across the forecast area with the front.
Thus will ramp up pops overnight, especially after 08z-09z. Patchy
fog will be possible overnight also. given the high dew points and
the arrival of clouds and moisture, lows in the upper 60s to lower
70s will be expected.

Saturday -

Active weather is expected. Chances for rain showers will persist in
the morning hours as the previously discussed warm front boundary
continues to lift northeast and the associated showers also exit to
the northeast during the morning hours. Southwest surface flow will
be left in place at the surface, allowing a bit more humidity and
heat to the airmass over Central Indiana along with a column that
will be much more favorable for convection. Meanwhile aloft, models
suggest the zonal flow will be in place and a quick moving wave will
be pushing across Indiana, arriving in the early afternoon and
exiting after 00Z Sunday. Forecast soundings suggest a very juicy
air mass with over 2900 J/KG of CAPE and pwats over 2 inches by mid
to late afternoon. HRRR suggests a line of TSRA development pushing
out of IL and across Indiana with this favorable air mass in place.
Furthermore, mid level flow is moderate, not stagnant, which could
lead to more organized, developed updrafts. Thus damaging winds,
lightning and very heavy rain will be possible with the passing
storms/QLCS through the afternoon and into the evening. Heavy rains,
should they occur, could lead to flooding with additional rainfall
possible on Sunday.

Given this outcome, Saturday should not be a wash out entirely, as
several dry hours will be expected in between the departing morning
system and the passing squall line during the afternoon and into the
evening.  Will trend highest pops in the mid to late afternoon, with
low to no pops during the 15Z-19Z window. Highs should once again
reach the upper 80s to near 90.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 244 PM EDT Fri Jul 18 2025

Fairly active weather early in the period will gradually shift to a
quieter but hotter pattern by mid week.

Zonal flow currently exists across the northern tier of the US,
roughly along and just south of the US Canada border. Guidance shows
ridging developing over the Plains this weekend allowing the jet to
become more northwesterly over the Midwest. Increased upper-flow
combined with a NW-SE oriented (but weakening) baroclinic zone
should allow for enhanced convective chances through the weekend.
Upstream convection may efficiently propagate our way if a sustained
cold pool can form.

Multiple rounds of convection are possible. Uncertainty will remain
quite high given how convection often depends on the previous round
of convection (placement of outflow boundaries, convectively
stabilized air mass, etc). These mesoscale dependencies will
compound within various convective-allowing models, so agreement
between models and run-to-run consistency is likely to be low. Take
individual model runs with a large grain of salt.

Severe potential will depend on storm mode, and given the pattern
that favors strong to damaging winds as convection may have a
tendency to congeal into an MCS. Additionally, flash flooding should
be a threat given the very humid air mass in place with repeated
rounds of storms possible. Some locations have already seen a lot of
rain recently, and in those places it wouldn`t take much more to
lead to flooding. Flash flood potential will be maximized where
storm motion is slower and/or repetitive. In the event of an MCS
this may occur along the SW flank where the trailing outflow
boundary more closely aligns with the mean wind.

As the ridge continues to build, the jet stream is expected to build
northward. That should act to reduce, but not eliminate, our
precipitation chances. Given the high humidity levels expected,
isolated to scattered showers and/or thunderstorms are possible each
afternoon. Storm mode should become more pulse-like given weaker
forcing and flow aloft.

Additionally, hot temperatures are likely to return as the core of
the ridge approaches. High in the 90s are once again possible.
Combined with high dew points in the 70s, heat indices approaching
advisory-level (105 degrees) are possible mid next week.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 738 PM EDT Fri Jul 18 2025

Impacts:

- MVFR Cigs possible late tonight into Saturday morning

- Fog possible at outlying TAF sites

- Showers and thunderstorms possible Saturday, primarily between 18-
  24Z

- Strong line of storms may move through around late afternoon or
  early evening Saturday

Discussion:

A warm front is expected to push northward late tonight. Lower level
moisture, and light winds may lead to some fog development and MVFR
cigs on the north side of the front as it passes across the TAF
sites. IFR visibilities cannot be ruled out at the more rural
airfields along with a brief period of IFR ceilings. Confidence is
limited so a brief tempo group was used to message when these
impacts are possible.

Isolated showers or storms are possible late tonight into Sunday
morning as the front lifts north, but confidence is too low for an
explicit mention. There is a greater chance for convection to
develop Saturday afternoon.

We are monitoring the potential for a large MCS to push through from
the NW tomorrow afternoon of which would bring a brief 15-30min
period of +TSRA and significant reductions. More detailed
information may be added in the TAFs in future updates as confidence
increases. Confidence is growing, but still feel there is too much
uncertainty so will stick with PROB30 at all sites from 18-24Z
tomorrow.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Puma
LONG TERM...Eckhoff
AVIATION...Melo