Brownsburg, Indiana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

974
FXUS63 KIND 191414
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1014 AM EDT Sat Jul 19 2025

.KEY MESSAGES...

- Strong to severe storms possible this afternoon and early evening,
  with damaging winds the primary threat. Heavy rain and flash
  flooding will also be threats, which will persist through the
  weekend into early next week.

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

&&

.FORECAST UPDATE...
Issued at 1014 AM EDT Sat Jul 19 2025

Showers and thunderstorms are developing over Illinois and should
gradually build eastward into the afternoon hours. As of right now,
storm activity is fairly disorganized but some hints of cold pool
development are noted across portions of central Illinois. A
stronger more mature cold pool and MCS near the Iowa/Illinois border
is also heading southeastward.

Our forecast challenge is how this activity will evolve as we head
into the afternoon. Storms ahead of the mature MCS may stabilize the
preceding air mass somewhat, which may mitigate our risk later on.
These storms may also congeal into an MCS of their own and affect
the western and southern portions of our area.

Storms closer to Knox County have been moving quite slowly and pose
a localized flooding threat. Flooding potential will be maximized
where storm motions are slow and favor a repetitive storm track.
Severe potential (mainly damaging wind gusts) will be favored where
a forward propagating MCS develops especially within embedded bowing
segments.

Otherwise, we reduced high temperatures a bit closer to the
convective area as cloud cover should be pretty thick through much
of the day.

&&

.SHORT TERM (Today and tonight)...
Issued at 338 AM EDT Sat Jul 19 2025

Primary concern for the short term is the threat for thunderstorms,
including a severe threat, and continued threat of heavy rain and
localized flooding.

The source of the local severe threat for today has developed
already over southern Minnesota/northern Iowa back into southeast
South Dakota and northern Nebraska. This activity should follow the
instability gradient southeastward into Iowa this morning,
continuing to propagate in a similar manner through the day.

Ample destabilization should occur through the day as a weak warm
front returns gradually northward across the area, though evolution
of the upstream MCS remains a bit uncertain given inconsistencies in
CAM solutions, likely owing to both some solutions developing
showers/storms ahead of the main complex and locally reducing
instability, and somewhat poor midlevel lapse rates. Nevertheless,
continue to anticipate at least some threat for strong to severe
storms this afternoon into early evening across central Indiana,
with scattered areas of damaging winds the primary threat, and a
secondary threat for isolated weak and brief QLCS tornadoes.

Additionally, precipitable water values will ramp back up
significantly today into tonight, near or above 2 inches, which will
pose a threat for heavy rain and localized flooding, especially
given ample rainfall in some areas in recent days. Warm rain
processes will contribute significantly with wet bulb zero heights
between 13 and 14kft, making for very efficient rainfall. HREF Local
Probability Matched Mean indicates potential for at least isolated 2-
3+ inch rainfall amounts in the next 24 hours, which, if falling in
particularly southern portions of the area which have seen as much
as 2-5+ inches in the past 3 days, could quickly produce flash
flooding.

The boundary is likely to remain somewhere in the area tonight,
though modulation of the same by this afternoon`s activity will have
a large role to play in exactly where it is located. Guidance
indicates potential for redevelopment along this boundary overnight
as modest WSW midlevel flow may serve as a source of lift along this
NW-SE oriented front. Expect that there will be at least a brief
break in activity this evening but how long this will last and where
exactly the redevelopment may occur is also uncertain given the
dependence upon evolution of earlier activity.

Highs will rise into the mid to upper 80s today - near seasonal
normals - with dewpoints recovering back into the mid 70s across
much of the area. Heat index values may reach into the mid to upper
90s as a result. Overnight, dewpoints will remain relatively high,
limiting diurnal cooling, which will keep overnight lows in the low
to mid 70s.

&&

.LONG TERM (Sunday through Friday)...
Issued at 338 AM EDT Sat Jul 19 2025

Widespread hot and humid conditions expected to return for the
latter half of the long term, with potential dangerously high heat
indices.  But first, more reasonable warm (yet humid) days to be the
rule late this weekend through Tuesday.

Sunday through Tuesday...

Canadian high pressure gradually tracking from the northern Great
Lakes to the Northeast will serve to keep the upper subtropical
ridge suppressed to the Heartland and points south.  Corresponding
cool front along the southern edge of this northern surface ridge
will push south through the region Sunday, with the frontal zone
likely eventually pushing well south of the CWA...yet with the
center of the high passing well to our north, expect limited
reduction in surface dewpoints through Tuesday.  Light east/
southeasterly breezes to be the rule through Monday and Tuesday as
the high passes to our north/northeast.

Scattered to perhaps numerous showers and t-storms will linger over
portions of the region amid the slowly passing frontal zone Sunday
into Monday.  With potential for stronger storms amid this north-
south instability gradient...although so far low confidence in
heavier rainfall amounts for any particular location.  Considerable
cloudiness with modest CAA will promote resultant mainly low to mid-
80s for highs Monday.  Most pleasant conditions likely around the
Monday night to early Tuesday timeframe when passing northern high
should build furthest south/west into the region.

Wednesday through Friday...

Surface ridge to rearrange and amplify along eastern seaboard,
encouraging a prolonged light to moderate southwesterly flow into
Indiana...which will serve to build the upper subtropical ridge
northward into the Midwest.  Widespread mid to possibly upper-70s
dewpoints will be the lead actor...coupled with afternoon highs
around the low 90s...to potentially produce daily maximum heat index
values around 100-110 degrees.  This would be the highest heat
indices so far this year, and would warrant Heat product headlines.

Cannot rule out widely scattered, diurnally-driven convection,
especially toward the end of the long term...when the next, albeit
likely weak, northern stream wave will attempt to drag modest
forcing into the Midwest.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 646 AM EDT Sat Jul 19 2025

Impacts:

- Patchy MVFR early in the period, primarily at BMG

- Showers and storms at times during the period, particularly this
  afternoon into early evening; strong to severe line of storms
  possible

Discussion:

Mostly quiet weather early in the period, though some patchy MVFR
conditions are present, primarily at BMG in fog. This fog will mix
out rapidly with sunrise.

The primary concern for aviation this period will be thunderstorms,
with the most likely time frame for convection being in the
afternoon to early evening hours. Have continued with PROB30 groups
at each site during the most likely time frame for storms. Strong to
severe storms will be possible.

Showers and storms cannot be ruled out tonight as well, though
uncertainty grows significantly with time. Will carry a VCSH mention
at LAF through the remainder of the period but not mention elsewhere
for the time being.

Winds outside of thunderstorms will generally be southerly or
southwesterly much of the period, 8-12KT or less.


&&

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

$$

UPDATE...Eckhoff
SHORT TERM...Nield
LONG TERM...AGM
AVIATION...Nield