Greybrook Lake, Indiana Weather Forecast Discussion

258
FXUS63 KIND 291400
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1000 AM EDT Mon Sep 29 2025
.KEY MESSAGES...
- Dry with unseasonably warm afternoons this week
- Patchy fog possible during the overnights
&&
.FORECAST UPDATE...
Issued at 1000 AM EDT Mon Sep 29 2025
Late season 90 degree day?
Another hot day expected across Central Indiana as high pressure
remains the dominant weather influence across the entire region. A
anomalously warm airmass kept in place by the ridging and high
pressure will lead to well above normal temperatures today and
through the week for Central Indiana...also resulting in rapidly
worsening drought conditions. Ample sunshine in addition to drying
grounds within this hot airmass create the perfect recipe for large
diurnal ranges where high temperatures often exceed guidance by
several degrees. Keeping high temperatures a few degrees warmer than
the National Blend of Models, with forecast highs in the upper 80s
to low 90s this afternoon based on the current weather set up today.
The main concern with hot and dry days this time of year is
hazardous fire weather conditions. Deep afternoon mixing into a dry
layer aloft may result in afternoon relative humidity values
dropping into the 20-30% range, potentially reaching critical
thresholds for fire weather. Light winds however should prevent fire
weather concerns from increasing.
Historically, the average last 90 degree day of the season for
Indianapolis is around the first week of September. While this late
season heat wave is occurring later that normal, highs today are not
expecting to reach or exceed record highs for the day.
&&
.SHORT TERM (Today and tonight)...
Issued at 259 AM EDT Mon Sep 29 2025
Be prepared for much of the same weather, as large
synoptic ridge with the width the size of the CONUS has rooted
itself aloft, of which will be reinforced by warm-core lows over the
atlantic and strong AVA over the Eastern Canadian Provinces. This
large upper level ridge is the primary culprit for the well above
normal temperatures we have been experiencing, especially in
combination with weak surface flow and 1020-1025mb surface high
pressure. Expect highs this afternoon to once again push well into
the upper 80s with 850mb temperatures remaining around 15C. A few
locations may reach or exceed 90 for brief periods this afternoon if
the near surface layer can become super dry-adiabatic.
Also continuing is the diurnal patchy dense fog threat due to the
same dry, clear and calm conditions creating large diurnal curves.
However, without a synoptically induced low level moisture source,
fog should be confined to near rivers and in agricultural areas /
farm fields.
For tomorrow, a slight cool down is possible as northeasterly
surface winds develop. Even so temps will still be well above normal
with highs in the mid 80s.
&&
.LONG TERM (Tuesday through Sunday)...
Issued at 259 AM EDT Mon Sep 29 2025
Confidence is increasing in a dry and warm mid to late week with
latest guidance presenting a stronger and broader upper subtropical
ridge over much of the central/eastern CONUS...including a H500
center drifting from northern Illinois to the lower Ohio Valley
while occasionally reaching a 588 dm height.  Meanwhile an equally
massive 1032 mb ridge of Canadian surface high pressure will slowly
follow a circular path around the top and eastern side of the upper
high, from northeastern Ontario to the Mid-Atlantic by Sunday.
Earlier forecast uncertainty surrounding the lingering trough over
southeastern states possibly nosing into the CWA`s far-southern
zones...has shifted to a noticeably lower-humidity solution with
both upper and lower ridges suppressing this feature down the
Appalachians to the Gulf coast through the mid-week.  Next upstream
mid-latitude wave is not expected to approach Indiana until the end
of the weekend...when possibly ample mid-level RH / column
precipitable water will struggle to get through the antecedent dry
boundary layer.
This will all translate to continued rain-free conditions amid warm
afternoons more closely resembling early September normals. Expect
another unseasonably warm day Tuesday with widespread mid-80s. Low
80s the rule for the remainder of the long term period, with the
surface high`s establishment along the eastern seaboard facilitating
light/moderate southerly breezes by the late week.  Generally mostly
clear skies will flank SCT/BKN decks through the Wednesday-Thursday
timeframe when the Canadian air mass first builds into the CWA while
sliding around the upper ridge...with highs perhaps only reaching
the upper 70s for several eastern zones on Thursday.  Morning lows
consistently in the 50s...should include early mornings around 50F
for northeastern counties through the midweek.  The normal max/min
at Indianapolis through the long term falls from 73/52 to 71/50.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 611 AM EDT Mon Sep 29 2025
Impacts:
- Brief MVFR conditions in fog possible at KHUF/KLAF through 13Z
Discussion:
VFR conditions are expected through the TAF period at KIND, outside
of brief MVFR conditions possible at KHUF/KLAF through the first
hour within patchy shallow fog. Diurnal cumulus is expected in the
afternoon at around 6kft. Winds will be light and variable this
morning before settling on a northeasterly direction this afternoon.
Winds will remain below 10kts through the TAF period.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...CM
SHORT TERM...Updike
LONG TERM...AGM
AVIATION...Updike

NWS IND Office Area Forecast Discussion