217
FXUS63 KIND 090322
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1122 PM EDT Wed Oct 8 2025

.KEY MESSAGES...

- FROST ADVISORY tonight across our northern counties.

- Patchy frost Tonight and Thursday nights with lows in the mid to
  upper 30s.

- Dry weather is expected through at least Tuesday, with gradually
  warming temperatures.

&&

.FORECAST UPDATE...
Issued at 939 PM EDT Wed Oct 8 2025

High pressure is providing clear skies this evening. Temperatures
were cooling as expected with loss of heating, but winds have
remained up, keeping the temperatures from plummeting.

Winds will diminish some but not go calm many areas with the center
of the high remaining north of the area. This will keep low
temperatures from reaching their coldest potential.

Some frost still looks likely across the north, especially in
sheltered and favored cold areas. Based on latest model temperature
probabilities and observational trends, went ahead and added
Montgomery and Boone Counties to the Frost Advisory.

Tweaked low temperatures for favored cold areas, and adjusted hourly
forecasts to match observational trends.

&&

.SHORT TERM (This evening through Thursday)...
Issued at 303 PM EDT Wed Oct 8 2025

Large-scale upper-level troughing and strong surface high pressure
will bring some of the coolest nights of the season so far. Surface
analysis shows northerly flow and cold air advection today
associated with the advancing 1032mb high. Continued cold air
advection is expected as we head into tonight.

By sunset, the surface high center should be located roughly over
Michigan. Since the high is still a bit to our north, we`ll have a
northerly breeze through the night. Therefore, radiational cooling
potential may not be fully realized. Still, cold air advection is
strong enough and the winds light enough to allow for lows in the
mid to upper 30s across our north. Slightly warmer values will be
found elsewhere with lows in the upper 30s to low 40s. Some wind-
sheltered areas may see some patchy frost tonight. We`ve added frost
to the forecast across our northern tier counties from Lafayette to
Kokomo to Muncie. Given that it may be the first frost of the season
for many of these places, a Frost Advisory will be issued with this
forecast update.

As for highs, full sun, dry air, and relatively light winds will
allow for a large diurnal spread. Temperatures may tend towards the
higher end of guidance and dew points may end up near the bottom.
We`ll add more weight to high-res guidance and MOS for temperatures
throughout the forecast period. Expect highs in the upper 60s to
near 70 on Thursday.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 303 PM EDT Wed Oct 8 2025

Continental air masses with good radiative conditions this time of
year often have a high temperature bias in models. For low
temperatures Thursday night, we used 10th percentile blended
guidance to account for this, and also nudged toward NAM 3-km for
better terrain representation. Strong subsidence and shallow
inversion in model soundings is a classic dew/frost setup, with
supportive temperature for frost across roughly the northern half. A
few outlying areas could reach freezing. Urban areas are less at
risk for frost and for now will not include frost for the core of
Indianapolis. One caveat may be cirrus preceding an upstream
midlevel wave, but current timing appears to have minimal impact
to the radiative cooling process other than perhaps slowing it
slightly toward sunrise.

Weak thermal ridging preceding the upstream shortwave trough will
bring our temperatures back to around normal Friday. There has been
a trend of this wave closing/deepening over the Great Lakes Friday a
little more substantially than earlier model cycles, and then
drifting south before dampening. This may nudge a cooler air mass a
little deeper into Indiana this weekend which could slightly counter
what would otherwise be an overall warming trend. This may be
especially true if post-frontal stratus is extensive. There may be
enough ascent and midlevel moisture for low coverage / low QPF
showers, late Friday into Saturday depending on the behavior of the
aforementioned midlevel wave. At this time, probabilities of
measurable rainfall amounts are <20 percent.

Next week, moderate-strongly positive midlevel heights from building
ridging will result in +5-10 degree temperature anomalies. A plume
of high-level subtropical moisture from the east Pacific and lower
tropospheric moisture returning on the western side of the ridge
will bring precipitable water to above climatology. Forcing is
minimal, however. Minor perturbations at the periphery of the ridge
is resulting in a light QPF signal in many ensemble members, but
overall rainfall probabilities and amounts will be minimal next
week.

For the Day 8-14 period, early indications in the medium-range
ensembles is for the ridge of deamplify and/or retrograde some with
a more active synoptic flow potentially leading to some moderation
in temperatures but probably still above normal. Precipitation
signal is near average in this pattern.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1122 PM EDT Wed Oct 8 2025

Impacts:

- None; VFR conditions expected

Discussion:

High pressure and broad subsidence moving through Indiana will
result in VFR Conditions and light winds through the TAF period.
Forecast soundings and time heights support this showing a dry
column.

Winds will slowly change from northerly to northeast as the surface
high drifts east to the eastern Great Lakes.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 5 AM to 9 AM EDT Thursday for INZ021-028>031-
035>042.

&&

$$

UPDATE...50
SHORT TERM...Eckhoff
LONG TERM...BRB
AVIATION...Puma