IND issues Area Forecast Discussion (AFD) at Aug 20, 1:03 AM EDT341
FXUS63 KIND 200503
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
103 AM EDT Wed Aug 20 2025
.KEY MESSAGES...
- Cooler tomorrow onward with dry weather through the rest of the
week
&&
.FORECAST UPDATE...
Issued at 1025 PM EDT Tue Aug 19 2025
Main focus for this evening's forecast update will be the incoming
stratus clouds from the north and chance for patchy fog across the
region.
Latest satellite and radar imagery show convection from earlier this
evening well south of the Ohio River while a low stratus deck
develops over much of the Great Lakes region. ACARs soundings show a
strong low level subsidence inversion setting up as high pressure
settles in over the area...working to trap leftover moisture within
the boundary layer leading to widespread stratus. These clouds have
already reached Kokomo and Lafayette and will continue to push
southward across most of Central Indiana through the night. In
addition to low clouds, wind sheltered areas may see patchy fog
overnight through around sunrise with how saturated the boundary
layer is. Lower confidence in how widespread fog may be as winds are
forecast to remain elevated overnight, likely limiting fog to
valleys and wind sheltered locations while low stratus engulfs the
rest of the region.
Cloud cover will be stubborn to lift and break up tomorrow as a
stable airmass aloft keeps clouds and moisture trapped near the
surface. Trended cloudier for tomorrow with this evening's update
and may have to keep low clouds around even longer in future
forecast updates based on trends. Lowered tomorrow's highs below
guidance as well due to increased clouds and cold air advection.
Most guidance likely has a warm bias coming off such a hot stretch
of weather, so would not be surprised if many areas stay below 80
degrees the next several days.
&&
.MESOSCALE UPDATE...
Issued at 452 PM EDT Tue Aug 19 2025
Numerous sub-severe thunderstorms are currently stretched in a quasi-
linear fashion from near Sullivan...to Bloomington...to near
Greensburg. These, rather narrow, cells will continue to slowly
track to the southeast while producing lightning, mainly brief
downpours, and occasional stronger wind gusts to around 40-50
mph. A non-zero threat of isolated severe winds over the next few
hours is greatest over southwestern central Indiana zones where
greater instability exists. Both small hail and brief ponding of
roads/low-lying areas cannot be ruled out from the few stronger
storms...yet little or no impacts are expected.
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 107 PM EDT Tue Aug 19 2025
Rest of Today and Tonight.
As of early this afternoon, shower coverage is minimal with the
widespread cloud cover gradually clearing as temperatures slowly
warm across central Indiana. The main area of focus for the next
round of thunderstorm development is along the differential heating
boundary across north central Indiana between the area of cloud
cover across the northern third of the state and the relatively
partly cloudy skies to the south. The front is currently entering
Warren and Tippecanoe counties from the northwest and exiting the
southeast towards 8PM. As the front crosses the differential heating
boundary, expect to see shower and storm coverage increase with a
southerly progression as it organizes. There will likely also be
some component that moves southwest as the best instability will be
closer to Vincennes by late afternoon.
The severe weather threat looks marginal at best but there is
increasing confidence that this complex will organize enough for a
cold pool and allow for some marginally severe thunderstorm wind
gusts.
Near Heat Advisory conditions are expected across the far
southwestern portions of the state ahead of the likely convection
with temperatures in the low 90s and dew points in the upper 60s to
low 70s. There may be a few spots that hit 105, but confidence in
the occurrence is fairly low and if it does it will be brief as
those higher end heat index values would also increase the threat
for rain-cooled air to impact the area due to the higher instability.
As we move into the overnight hours the front will move south
towards the Ohio River with rain chances coming to an end. Surface
flow will become increasingly northerly through the overnight hours
but dew points will only fall into the mid 60s as the source of the
air is relatively moist. Overnight lows will fall into the mid to
upper 60s with lingering low and mid clouds helping to insulate
temperatures. There could be some fog but expect with the drier air
advecting into the area that coverage will be minimal, especially
with the mostly cloudy to cloudy skies.
Wednesday.
Residual saturation behind the exiting front will keep cloudy skies
around through much of the morning but with the front well to the
south, no additional precipitation is expected outside of a low-end
threat for some morning drizzle towards daybreak. This cloud cover
will also help to keep temperatures mild with daytime highs in the
low to mid 80s.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 107 PM EDT Tue Aug 19 2025
Wednesday Night Through Friday.
Cooler weather is expected to continue in the aftermath of the
frontal passage with northerly surface flow helping to keep to keep
temperatures mild with much lower dew points. Model soundings show
favorable conditions for diurnal cu Thursday with dry air and
subsidence above a nearly saturated boundary layer with less
favorable conditions on Friday as the RH is closer to 80 percent.
Saturday Through Tuesday.
The next system that initially looked likely to move through Friday
night into early Saturday continues to slow due to the exiting
hurricane off the east coast with timing for the frontal passage
looking more like late Saturday. The parent low pressure system is
well into Canada with little forcing this far south, but do think
there will be at least a few showers and thunderstorms but nothing
widespread.
A much stronger push of cold air is expected behind this frontal
passage with good model agreement in overnight lows dropping into
the low 50s with DESI probabilities showing a 20-50 percent of sub-
50 degree lows Monday night into Tuesday with the highest chances
towards Muncie. There could be a few showers with steep lapse rates
aloft due to the strength of the cold air advection but forcing is
minimal and without signs of weak shortwaves within the broader
flow, chances look too for a mentionable POP at this time.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 103 AM EDT Wed Aug 20 2025
Impacts:
- MVFR stratus becoming predominant overnight and persist into
Wednesday morning. IFR cannot be ruled out.
- Patchy fog possible overnight
Discussion:
An area of stratus, with many holes in it, will continue to push
south overnight. The stratus will eventually fill in. Conditions
may bounce between VFR and MVFR early but then should settle into
MVFR. Patches of IFR cannot be ruled out.
Given a still moist lower atmosphere, some patchy fog may develop
overnight.
Stratus will gradually lift and become a cumulus field during the
day Wednesday, with conditions returning to VFR by early afternoon.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...CM
SHORT TERM...White
LONG TERM...White
AVIATION...50
Source:
IND issues Area Forecast Discussion (AFD) at Aug 20, 1:03 AM EDT---------------
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