Zionsville, Indiana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

347
FXUS63 KIND 201738
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
138 PM EDT Sun Jul 20 2025

.KEY MESSAGES...

- Flash Flood Watch in effect 1 PM today through 8 PM Monday

- Multiple rounds of showers and storms are expected today into
  Monday, with locally heavy rainfall and flash flooding possible

- Strong to severe storms will be possible today into tonight, with
  damaging winds the primary threat, although large hail or an
  isolated tornado cannot be ruled out

- Hot and very humid next Wednesday-Friday, yielding widespread and
  potentially dangerous maximum heat indices in the 100s.

&&

.MESOSCALE UPDATE...
Issued at 859 AM EDT Sun Jul 20 2025

A cluster of storms is becoming better organized just over the
Illinois border northwest of Warren and Tippecanoe counties. Signs
of cold pool propagation are noted on radar, and some hints of a
rear inflow jet are also beginning to take shape.

As of right now, the cluster is only loosely organized. However, it
has potential to become a bit better organized as it heads
southeastward into Indiana. Some factors working in its favor
include a NW-SE oriented instability gradient stretching from about
Lafayette to Muncie. Additionally, a perturbation aloft is providing
modest large-scale lift. Enhanced mid-level flow likewise is
allowing the system to maintain a semblance of cold-pool shear
balance and thus storm-scale organization.

Some factors working against it include weak low-level flow which
may allow cold pool shear balance to be lost at times, causing the
system to become occasionally outflow dominant. Furthermore, shear
vectors aren`t exactly parallel with the instability gradient which
may cause the best region of cold pool shear balance to be off
gradient (allowing the system to propagate into more stable air).
Preferential growth should still tend towards the greater
instability (southeastward).

Given the competing factors, a highly organized MCS charging across
Indiana is not currently expected. However, there is enough going
for it that a few instances of briefly organized bowing segments are
possible. These bowing segments, should they occur, will feature the
greatest potential for severe weather. Strong to damaging wind gusts
are the primary severe hazard.

Additionally, very heavy rainfall is occurring with these storms and
some localized flooding remains possible. Additional storm
development later in the afternoon may exacerbate this threat.
Subsequent storm development will depend on how this first round of
storms evolves through the morning.

&&

.SHORT TERM (Today and tonight)...
Issued at 346 AM EDT Sun Jul 20 2025

Primary concerns through the next 24-30 hours will be multiple
rounds of storms possible along a remnant surface boundary and
multiple outflow boundaries, as well as a threat for strong to
severe storms today into tonight.

While confidence is fairly high in the occurrence of multiple rounds
of precipitation in the short term, confidence in exact details is
modest at best given both the mesoscale dependencies which will
heavily influence each subsequent round of convection, and the
difficulties even high resolution convective allowing models have
with resolving details in such weakly-forced environments. As prior
discussions have mentioned, individual CAMs should be taken with a
grain of salt.

That said, an extremely moist airmass is in place across the area,
with column precipitable water values near or in excess of two
inches, which is near climatological maximum, and this airmass will
remain in place through tonight into Monday. In addition, wet bulb
zero heights frequently in excess of 13kft and deep saturation will
promote highly efficient warm rain processes. Portions (though not
all) of central Indiana have received significant rainfall in recent
days, and HREF local probability matched mean progs indicate
significant chances for rainfall amounts of 1-3+ inches over the
next 24-36 hours, and pockets of higher amounts are a significant
possibility given the aforementioned circumstances which will
promote very high rainfall rates in convection. With multiple rounds
of storms likely, and at least some potential for training depending
upon how boundaries become oriented or reoriented with time, and the
aforementioned high rain rate potential on fairly saturated ground
in some areas, flood potential is a significant concern.

Despite uncertainties with respect to the exact evolution of storms
and placement of highest rainfall amounts, in collaboration with
neighbors, will go ahead with a Flash Flood Watch for all of central
Indiana through Monday.

Today into tonight, bulk shear values will be a bit more robust than
in recent days, and diurnal heating will result in ample
destabilization ahead of the initial round of convection currently
over the mid Missouri and Mississippi valleys, which may promote
intensification or additional development with this activity as it
pushes into the area later today. Redevelopment of organized
convection may occur as the day wears on along the outflow boundary
left behind by round one, which will also potentially move into the
area later today into tonight. Damaging winds will be the primary
threat, though an isolated tornado or large hail report cannot be
ruled out given the relatively robust shear values.

A fairly wide range of high temperatures (low 80s to low 90s) is
expected today, with midday/afternoon storms in round one likely to
suppress heating across the north, while later activity in the south
will allow temperatures to rise to near or above 90. Lows tonight
will be near expected dewpoints in the upper 60s to mid 70s.

&&

.LONG TERM (Monday through Saturday)...
Issued at 346 AM EDT Sun Jul 20 2025

Monday and Tuesday...

Flash Flood Watch to continue into early evening Monday as the
lingering cool frontal boundary remains stretched from WNW-ENE along
and south of the I-74 corridor.  Corresponding dewpoint gradient to
range from perhaps upper 70s over southwestern counties to mid-60s
near/east of Muncie.  Considerable cloudiness and at times scattered
to possibly numerous showers may actually bring the lowest maximum
temperatures in nearly two weeks over the regions northeastern half
where low 80s are expected.  Overall light rainfall is expected, but
Flash Flood Watch is in effect through end of the day Monday given
potential for areas of moderate/heavy rainfall...which may impact
areas with ample antecedent/recent rains.

Tuesday should be the most pleasant day of the long term, albeit
still sporting seasonably very warm and humid conditions.  The brief
taste of milder air from the passing northern surface ridge should
be greatest around dawn Tuesday when readings should drop to the low
60s over the region`s northeastern corner...with forecast lows along
the I-74 corridor in the mid-60s.  Mainly dry conditions Tuesday
should include a few afternoon showers near and south/west of
Bloomington, with most locations rebounding to the mid/upper 80s as
moderate humidity is quickly replaced by mainly 70-75F dewpoints by
the evening hours.

Wednesday through Saturday...

Upper subtropical ridge to build northward around the Tuesday night
timeframe and encapsulate Indiana and many surrounding states
through the end of the week.  This will set the potential stage for
another heat wave for most/all of the local region into this
weekend...although more concerning than the marginally-hot
afternoons will be anomalously high dewpoints maintained in the mid
to upper 70s, starting Wednesday afternoon.  Heat index values to
diurnally vary from around the mid-70s to potentially the 100-110
degree range. These afternoon maxima heat indices would be equal to
or slightly greater than those experienced amid the late June heat
wave.

Somewhat lower confidence in temperatures reaching the low 90s / and
heat indices exceeding 100 for the Friday-Saturday timeframe per
increased daytime convective/corresponding cloud chances.  Rain
chances are expected to exhibit an increasing trend from near-zero
Wednesday...to most-likely isolated cells Thursday...to more
scattered late-day showers/ t-storms through the late week.  The
late-week should see the pattern shift slightly east, which will
allow a ribbon of anomalously high precipitable water to slide into
the CWA amid weak forcing from a subtle southern end of a H500 wave
crossing the Great Lakes.  A few torrential downpours would be the
primary concern from any storms, with perhaps localized flooding
possible for any areas that saw heavy rain on consecutive days.
Organized severe weather appears unlikely given overall lack of
shear...although a few stronger cells could be possible around the
Thursday night timeframe under the passing wave.  The normal max/min
at Indianapolis from July 23 to August 14 is 85/66.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 138 PM EDT Sun Jul 20 2025

Impacts:

- VFR Conditions this afternoon and evening.

- MVFR or IFR late overnight

- Scattered showers or thunderstorms possible this afternoon and
evening.

Discussion:

A stalled frontal boundary over Central Indiana has allowed for a
very moist and stagnant air mass to remain across Central Indiana.

An upper level disturbance was exiting Central Indiana. This was
allowing scattered light rain showers across northern Central
Indiana to depart to the east. A few more showers were found
upstream, over central IL, but these were weak and IR shows no
significant cooling cloud tops. HRRR suggests redevelopment along
the boundary this afternoon, but confidence for this is low as
daytime heating has had a minimal impact due to thick cloud cover
across the sites. For now, a VCTS mention has been used.

The lingering lower level boundary and moisture is expected to remain
in place across the area overnight, with very high dewpoints, light
winds and low dew point depressions. This should again result in fog
overnight, some of which may become IFR or LIFR, mainly at the more
rural TAF sites.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Monday evening for INZ021-028>031-035>049-
051>057-060>065-067>072.

&&

$$

SHORT TERM...Nield
LONG TERM...AGM
AVIATION...Puma