IND issues Area Forecast Discussion (AFD) at Sep 21, 12:52 AM EDT466
FXUS63 KIND 210452
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1252 AM EDT Sun Sep 21 2025
.KEY MESSAGES...
- Isolated to scattered showers and storms possible through the
night
- Scattered afternoon showers and storms possible on Sunday.
- Daily chances for showers and a few t-storms next week.
&&
.FORECAST UPDATE...
Issued at 1022 PM EDT Sat Sep 20 2025
A major weather pattern change is currently underway across the
Midwest as we transition from drought conditions to a parade of
storm storms this coming week.
Troughing in place across the Upper Midwest places Indiana within a
southwest flow pattern aloft with multiple waves bringing chances
for showers and thunderstorms to the region tonight through much of
next week. Satellite and radar imagery show numerous clusters of
convection stretching from Oklahoma to Indiana and northward through
the Great Lakes on the leading edge of the trough. A weakening
cluster of showers and storms has slowly been progressing
northeastward through Central and Western Indiana late this evening.
The environment across Indiana and points east is very dry, with
deep low level dry layer making it difficult for convection to
sustain itself as it moves eastward. In addition to such dry air in
place, the best forcing and dynamics still remain to the west
tonight, so most of the showers and storms moving into Indiana
tonight will likely be weakening and under severe limits. Low
confidence exists that the current cluster of convection will make
it east of the I-65 corridor as GOES Lightning Cast has shown a
considerable diminishing trend in lightning and lightning probs in
the last several scans. Radar shows the entire cluster falling apart
with scattered cells developing along a gust front racing eastward.
Showers and a few thunderstorms are still possible over the next
several hours for portions of Central and North Central Indiana, but
do not expect widespread measurable rainfall until tomorrow
afternoon into Monday. Keeping scattered showers and thunderstorms
in the forecast for much of Western and Central Indiana through the
night as a weak LLJ develops overhead, but confidence in any specific
area observing rainfall is fairly low due to the disorganized
nature of these storms within a weakly forced and weakly sheared
environment.
&&
.SHORT TERM (This evening through Sunday)...
Issued at 203 PM EDT Sat Sep 20 2025
Surface analysis early this afternoon shows a large and broad area
of high pressure over Ontario, extending its influence south and
west to include the east coast, the Ohio Valley and deep south. Low
pressure was found over the Dakotas and over OK. Looking aloft,
water vapor showed a negatively tilted trough from the northern
plains across IA to Indiana. The subsidence that has been persistent
across Central Indiana for quite some time is gone. An upper low at
near the bottom of the trough was found over NE IA. Water vapor
shows plenty of mid and upper level moisture over Indiana within the
trough. Radar Mosaics shows isolated showers over IL Dew points
across the area remained high, in the upper 50s and lower 60s.
Tonight...
Models suggest the upper trough will continue to swing through
Indiana this evening and overnight, providing forcing. Forecast
soundings fail to show deep saturation as lower level organization
is lacking due to the broad high pressure system. HRRR continues to
suggest isolated-scattered shower and storm development this
afternoon and evening, and given forecast soundings suggesting
attainable convective temperatures long with precipitation upstream
in IL, chance pops are still warranted, mainly during the evening
hours. Isolated thunder will remain possible. Otherwise, expect
mostly cloudy skies overnight...due to mid and high cloud as the
upper trough swings across Indiana. Lows should be a little warmer
due to cloud cover, in the lower to middle 60s.
Sunday...
Models on Sunday continue to suggest a broad trough-like pattern
aloft over Indiana on Sunday, but best forcing in the area looks to
remain over MI and well to the west near the Mississippi valley. Mid
levels are suggest to be dry in the wake of the departing trough.
However, forecast soundings do again suggest shallow CAPE available,
favorable for diurnal convection. Again with little support within
the lower levels and aloft, daytime heating appears to be the best
trigger. Thus only some minimal, low confidence pops will be used,
during the afternoon hours. Overall, there is little change in the
air mass, so highs in the middle to upper 80s will once again be
expected.
&&
.LONG TERM (Sunday night through Saturday)...
Issued at 203 PM EDT Sat Sep 20 2025
Strong ridging over the Western Conus has led to broad but weakly
forced troughing over the Plains, of which will slowly push into the
Great Lakes and Ohio valley this weekend into early next week.
Although the longwave pattern is weakly forced, meso-alpha scale
shortwaves within the broad flow are expected to be relatively
strong inducing moderate lift across the region. This will likely
lead to periodic rain and storm chances to begin the week. There is
some uncertainty on timing, but generally the greatest rainfall
chances for early next week are expected to be Monday morning and
then again Monday night with diurnally induced convection in the
afternoons each day. Temperatures will remain elevated, but
curtailed by widespread cloud cover. This will lead to surface
environments of upper 70s over upper 60 dewpoints, so comfortable
but somewhat muggy for mid to late September.
As we reach the middle of the week, there is a large consensus on a
quickly dropping mid to upper level trough becoming cut off from the
parent upper level flow. However, this consistency does not continue
to the surface with a wide range in possible outcomes with the track
of the associated surface low. Generally, this should lead to
overall cooler and wetter conditions for Wednesday onward, but total
QPF varies greatly depending on where the low tracks. A more
northern track would lead to more sporatic rain chances, where as a
southern track could lead to a more consistent moderate to light
rain to end the work week.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1252 AM EDT Sun Sep 21 2025
Impacts:
- Scattered convection continues at times through the day
- More numerous showers and some storms tonight
Discussion:
Outside of convection, VFR conditions are expected through 06Z
Monday.
Showers and a few thunderstorms are possible during the entire
period as rounds of forcing move through, but confidence in specific
timing is low. Will use generic VCSH, and then use PROB30s to
indicate times when coverage should be higher.
One round of more coverage is expected in the predawn hours, with
another round probably developing this afternoon. More widespread
showers will move in tonight.
Drier low levels will keep ceilings outside of convection VFR
through 06Z Monday. Winds may vary with boundaries from convection.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...CM
SHORT TERM...Puma
LONG TERM...Updike
AVIATION...50
Source:
IND issues Area Forecast Discussion (AFD) at Sep 21, 12:52 AM EDT---------------
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