IND issues Area Forecast Discussion (AFD) at Sep 27, 7:30 AM EDT315
FXUS63 KIND 271130
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
730 AM EDT Sat Sep 27 2025
.KEY MESSAGES...
- Patchy fog tonight across central Indiana
- Dry and unseasonably warm through Monday, highs in the 80s
- Slight downward trend in temperatures Tuesday-Thursday to only
slightly above normal...while continued dry under ample sun
&&
.SHORT TERM (Today and tonight)...
Issued at 300 AM EDT Sat Sep 27 2025
Weak upper level troughing will make way to weak upper level riding
in response to height rises in front of a cut-off low over the four
corners region. Surface impacts to this low amplitude upper level
shift will be minimal, with slight decreases in dew points and
therefor larger diurnal swings each day. The main forecast problem
during the short term will be the potential development of patchy
fog. Broad subsidence maintained clear skies, with surface
temperatures quickly falling towards saturation. Luckily tonight,
dew point depressions are even greater, decreasing the coverage of
any fog development this morning. That said, given calm winds low
lying valleys or waterways are likely to fog up with visibilities
between 1-5SM between 9 and 12Z.
Temperatures will be slightly warmer today with central Indiana
under greater subsidence and therefore more efficient near surface
warming processes. Given 850mb temperatures around 15C and an
afternoon near dry adiabatic PBL; surface temperatures are likely to
push into the low 80s with a few areas reaching 84 to 85F.
Conditions for fog should become less favorable Saturday night as
additional ground moisture evaporates throughout the day. Still,
moisture is abundant enough for now that some instances of dense fog
cannot be ruled out. The best chance of fog is in areas that saw the
most rainfall, in agricultural/rural areas, and along river valleys.
&&
.LONG TERM (Sunday through Friday)...
Issued at 308 AM EDT Sat Sep 27 2025
Broad-headed upper subtropical ridge extending from the northern
High Plains to southeastern Ontario on Sunday...will morph into a
quasi cut-off of dry and unseasonably high heights over the Great
Lakes and Midwest into the midweek...courtesy of a rather broad, yet
overall weak/disorganized upper trough retrograding over the
southeastern CONUS into the Ohio Valley. A potential tropical
storm/hurricane approaching the Carolina coast into the Midweek may
track into the southeastern trough, and potentially bring showers
into Kentucky. Higher confidence surrounds the strengthening
northern jet riding zonal above the upper ridge...which should shift
a strong autumnal surface ridge from central Canada at least
partially into the Midwest...if not entirely so by the late week as
latest guidance is suggesting.
This will translate to a often mostly clear long term, with probably
SCT high cloud around Tuesday-Wednesday off of the tropical
circulation. The alignment of the upper ridge will promote
northeasterly flow, although the lack of surface gradient early in
the period will struggle to produce 10 mph flow. The increasingly
active pattern between the approaching trop and plunging Canadian
high will promote gusts around 10-15 mph during midweek afternoons.
Unseasonable warmth will be the rule under the upper ridge through
the early week. Sunday's normal high in Indianapolis is 74F, with a
record of 91F...the current forecast max is 86F.
The midweek gusts flowing out of the staunch Canadian surface ridge
centered over Hudson Bay...will facilitate a subtle but steady drop
in readings. This should translate to afternoon maximums steadily
decreasing from mid/upper 80s on Monday to around mid/upper 70s by
Thursday. While overnight minimums will likely display a drop from
above normal upper 50s to more seasonable readings across the
Wednesday timeframe.
Have kept all long term periods rain-free across the IND CWA,
although some guidance members continue to bring at least isolated
showers through the Ohio Valley to our far southern zones within the
late Tuesday to Wednesday night timeframe. While stray showers are
possible within this window near US-50...it would take a lobing vort
to be swung by the weakening tropical circulation over South
Carolina, as far west as the Middle Mississippi Valley to have
associated moisture make it through very dry lower levels.
Confidence so far here is low, yet will be reassessed with future
updates.
While fire weather conditions are unlikely, especially following
moderate to heavy rainfall earlier this week...daily minimum
relative humidity values will drop to near 30 percent amid the
unseasonable warmth Sunday-Monday, and again Thursday-
Friday...albeit never with higher gusts. The normal max/min at
Indianapolis during the long term falls from 74/52...to 71/50.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 730 AM EDT Sat Sep 27 2025
Impacts:
- Brief IFR/MVFR possible in fog through 13Z at KHUF/KLAF
Discussion:
Brief MVFR/IFR conditions in fog is possible at KHUF/KLAF through
13Z, although any reduced visibility will most likely be brief or
intermittent.
VFR conditions will otherwise continue to prevail over central
Indiana terminals into Sunday morning...as an upper ridge builds
over weak surface high pressure stretched across the Midwest.
Continued very light winds will often be variable during
morning/overnight hours, with generally westerly headings this
afternoon at KIND/KLAF. Expect areas of FEW to perhaps SCT afternoon
cumulus today.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
SHORT TERM...Updike
LONG TERM...AGM
AVIATION...AGM
Source:
IND issues Area Forecast Discussion (AFD) at Sep 27, 7:30 AM EDT---------------
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