Chapelhill, Indiana Weather Forecast Discussion

499
FXUS63 KIND 260202
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1002 PM EDT Thu Sep 25 2025
.KEY MESSAGES...
- Fog expected late tonight and early Friday with patchy dense fog
  possible over northern counties
- Warm and dry weather resumes Friday through most if not all of
  next week, with above normal highs often near the low 80s
&&
.FORECAST UPDATE...
Issued at 1001 PM EDT Thu Sep 25 2025
Main focus for the overnight period will be tracking the developing
fog across central Indiana with increasing confidence in significant
coverage of fog across north central and east central Indiana with
the potential for widespread dense fog. Models are showing good
agreement in a window for fog from 08Z to 13Z as skies continue to
clear in an ideal radiational cooling environment. Recent wet
weather is helping to increase near surface saturation and with
cooler air slowly working into the area, expect to see near
saturation across most if not all of central Indiana.
Contemplated a Dense Fog Advisory ahead of the fog formation, but
there remains some uncertainty as to the extent of the dense fog
which made it difficult to nail down where to issue for, but
currently confidence is highest in an area generally east of
Lafayette and north of Indianapolis. Will continue to track the
observational trends and make adjustments accordingly.
&&
.SHORT TERM (This Evening through Friday)...
Issued at 244 PM EDT Thu Sep 25 2025
Stratocu has been incredibly stubborn to mix out to this point but
the thicker cloud deck is now as of 18Z largely confined to far
eastern counties in closest proximity to the upper trough axis. A
few showers linger across eastern Indiana as well. Temperatures were
in the upper 60s over eastern counties with low to mid 70s further
west where breaks in the clods were allowing for some sunshine.
The upper trough axis will finally pivot to the east of the area by
early Friday and be replaced by rising heights as ridging aloft
expands east towards the region. With the upper trough still in the
area...cannot rule out a few additional showers over the east into
the early evening with another extended period of dry weather
commencing overnight into Friday and beyond.
The influx of drier air from the west will continue to slowly but
steadily decrease cloud coverage over the next several hours.
However with the upper trough axis lingering over eastern Indiana...
a few showers will remain possible through or just after sunset
before diminishing. The bulk of the deeper low level moisture and
low clouds will shift into Ohio overnight but there is potential as
winds veer to northerly for at least scattered stratocu to drift
back west into far eastern portions of the forecast area during the
predawn hours.
The much bigger impact however is likely to come from the
development of fog late tonight and early Friday. Model soundings
show a saturated near surface layer under a shallow inversion. With
skies clearing this evening and winds becoming light overnight...
really good setup is in place for patchy ground fog over much of the
forecast area with a particular focus over northern counties where
greater coverage of fog along with the potential for patchy dense
fog will exist. Trends will need to be monitored through the evening
and early overnight as fog develops for any enhanced messaging but
for now will highlight via the HWO and social media graphics. Fog
will burn off quickly after sunrise Friday setting the stage for a
dry yet pleasant day. Enough lingering moisture within the boundary
layer will likely support establishment of a scattered cu field for
the afternoon.
Temps...coolest night in two weeks is expected for much of the
forecast area with lows in the lower 50s. Low level thermals support
mid to upper 70s for Friday.
&&
.LONG TERM (Friday Night through Thursday)...
Issued at 244 PM EDT Thu Sep 25 2025
Although astronomical fall began a few days ago, Central Indiana
will continue to see warm and dry conditions that feel more like
late August/Early September through the extended. These warm and dry
conditions are due to the influence of a broad upper ridge building
over the plains that will gradually extend into the western Great
Lakes by late this weekend. Meanwhile, an upper level trough moving
through the region today will gradually move east and become nearly
stationary along the Appalachians owing to the influence of a
building Bermuda high off the mid-Atlantic seaboard.
High temperatures this weekend will be in the low-mid 80s area wide
/about 10 degrees above normal/. Thanks to fairly long nights and
dewpoints in the 50s, low temperatures are expected to be 50s closer
to normal, with the warmer conditions in the mid-upper 50s in the
larger cities due to urban heat island effects. Generally winds will
be light and variable Friday night through Saturday night, which may
lead to another night or two of patchy fog in outlying areas
especially those that saw the most rainfall in the last 24 hrs.
Since model guidance is mixed on this fog potential will leave these
conditions out of the forecast for now. By Sunday, winds will become
more N-NE, remaining light, thanks to building high pressure over
the Great Lakes.
Attention turns to the developing tropical system (Invest 94L)
currently near Hispaniola. There is very good agreement in the
hurricane and ensemble models showing this system to strengthen and
move towards the SE Atlantic coast by late Monday or Tuesday. The
interaction of this system with the upper trough over the
Appalachians will lead to a bit of a slingshot effect with the
tropical system, with light precip possibly getting as far west as
Central Indiana on Wednesday. 12Z Euro has backed off on this
potential and NBM paints generally 5-10 percent pops for the period.
Sufficient uncertainty exists to preclude to change to a day 6 POP
forecast, but trends and later forecast guidance will continue to be
monitored. The most likely influence of this tropical system will be
an increase of the NE surface winds thanks to an increasing pressure
gradient and advection of drier air from the Great Lakes/Eastern
Canada. As a result, temperatures may actually warm into the mid-
upper 80s /depending on extent of mid-high cloud cover/ thanks to
increased low level adiabatic mixing Monday into Tuesday. Slightly
cooler, but still above normal high temperatures are expected for
Wednesday into Thursday with greater cloud cover and weak CAA
expected to move in from the east during this time period.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 704 PM EDT Thu Sep 25 2025
Impacts:
-Brief LIFR conditions due to FG 08Z to 13Z
Discussion:
VFR conditions expected through the TAF period outside of a period
of IFR to LIFR cigs/vsbys as fog develops across central Indiana.
Confidence in the fog is highest at LAF with lower potential for HUF
and BMG. The timeline for fog looks to be as early as 08Z but most
likely in the 11-13Z timeframe. Winds will remain light and variable
through the TAF period with a predominately northerly direction.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...White
SHORT TERM...Ryan
LONG TERM...Crosbie
AVIATION...White

NWS IND Office Area Forecast Discussion