Advance, Indiana Weather Forecast Discussion

463
FXUS63 KIND 201803
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
203 PM EDT Sat Sep 20 2025
.KEY MESSAGES...
- Isolated to scattered showers and storms possible late this
  afternoon and evening.
- Scattered afternoon showers and storms possible on Sunday.
- Daily chances for showers and a few t-storms next week.
&&
.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 (18Z TAF Issuance)...
Issued at 1207 PM EDT Sat Sep 20 2025
Impacts:
- Mainly VFR Conditions
- Showers and isolated thunderstorms will be possible 21Z-09Z.
Discussion:
An upper level trough arriving over the area along with forecast
soundings indicating shallow CAPE available this afternoon and
evening will allow for shower developing later today. HRRR shows
scattered shower and storm development this afternoon as convective
temperatures are reached.
As heating is lost this evening broad lift continues and HRRR
suggests continued sct-isolated coverage, but confidence for this is
low for the moment.
Overall will use VCSH groups to cover the best windows for potential
rainfall. Will not mention thunder for the moment due to low
confidence on coverage and timing, rather using updates to address
this when confidence is high.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Puma
LONG TERM...Updike
AVIATION...Puma

NWS IND Office Area Forecast Discussion