309 
FXUS63 KIND 201607
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1207 PM EDT Sat Sep 20 2025

.KEY MESSAGES...

- Very warm temperatures again today

- Isolated to scattered showers and storms will be around today
  through Sunday...with strong gusts possible in storms late Sunday

- Daily chances for showers and a few t-storms next week...while 
  higher humidity keeps overnights warmer, clouds bring milder days

&&

.FORECAST UPDATE...
Issued at 935 AM EDT Sat Sep 20 2025

Surface analysis late this morning 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. Dew points across the area remained high, in the upper 50s 
and lower 60s.

Forecast soundings this afternoon suggest that convective 
temperatures will be reached this afternoon while shallow 
CAPE...values around 800 J/kg...will be available. HRRR suggests as 
convective temps are reached by late afternoon, a weak wave pushing 
around the trough will trigger some isolated to scattered showers 
and storms. Areal coverage appears rather limited at this point, and 
most locations will remain rain-free, but confidence is high for at 
least a few scattered storms on Radar late this afternoon. Thus will 
include 30-40 pops at many spots late this afternoon, but dry 
weather will be expected until at least 3pm. Ongoing highs in the 
middle to upper 80s appear on the mark.

&&

.SHORT TERM (Today and tonight)...
Issued at 257 AM EDT Sat Sep 20 2025

Central Indiana will remain under the increasing influence of an 
upper trough throughout the short term period. Heights will fall 
some today. At the surface, a weak front will remain northeast of 
the area.

Impulses will bring forcing at times as they move through the upper 
trough. These will interact with increasing moisture to produce some 
isolated to scattered showers and storms through tonight.

Trends on satellite show that there will be some sunshine today with 
breaks in the mid and high clouds. This will allow some instability 
to build this afternoon, but it will be low enough that severe 
storms are not expected. This instability be what allows the most 
coverage of convection.

Tonight, 850mb winds increase some, which could add additional 
forcing to the mix. 

Uncertainty remains in the timing and strength of the upper 
impulses, so confidence in the specific PoPs is lower than desired.

Given all of the above, will keep PoPs no higher than the chance 
category. Will generally time the highest PoPs in the afternoon and 
then again overnight as 850mb winds increase and moisture deepens.

The expected sunshine today will allow temperatures to peak in the 
middle and upper 80s. Clouds and increasing moisture will keep 
temperatures in the lower and middle 60s for lows tonight.

&&

.LONG TERM (Sunday through Friday)...
Issued at 257 AM EDT Sat Sep 20 2025

Sunday through Tuesday...

Broad and slowly-progressing troughiness will prevail over much of 
the northern CONUS through the early week...with somewhat-organized 
group of weaker short waves circulating around the southern side of 
a parent axis near Duluth...from the central Plains to the Midwest.
Despite overall unimpressive gradients...central Indiana's proximity 
on the southeast quadrant of the wide region of lower heights...will 
promote moderate SSW breezes that will slowly increase deep moisture 
into the mid-week.

Occasional scattered to at times numerous rain showers should be the 
rule...with greatest rain chances in the late Sunday night through 
Monday night timeframe...when a linear vort aligned parallel to the 
moisture advection slowly pushes east through the region.  Mainly 
isolated thunder will be favored during PM hours when modest daytime 
heating assists convection.  Diurnal ranges of 15 degrees or less 
are expected between considerable daytime cloudiness and warmer 
overnights amid unseasonably high dewpoints near the 65-70F range.

Wednesday and Friday...

Recent model trends are increasing rain chances into the late 
week...with the potential for the retracted northern jet to 
facilitate two vorts dumbbelling around each other in a broad cut-
off H500 trough centered near the Quad Cities area.  While lower 
confidence still surrounds the details of this set-up...there is a 
good chance the local region stays on the more humid/showery 
southeast side of any such cut-off...while positioned close enough 
to the spinning vorts to continue chances of at least scattered 
showers. Expect occasional isolated thunder chances, with overall 
lower chances for storms than the first half of the long term.

Highs in the 70s are most likely.  Lower certainty for overnight 
lows, dependent on if the humid Gulf fetch is maintained, or if the 
cooler cut-off core spins over the region...with this downward trend 
in morning minimums to near normal levels more likely towards the 
end of the long term.

Low confidence in total rainfall amounts for this upcoming week, 
given all of the pattern's moving synoptic parts, and what should be 
several, if not numerous rounds of showers.  Certainly the potential 
for widespread 1.00-2.00 inch totals is present, yet amounts will be 
refined as this much-needed rainy forecast is updated into next 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.
&&

$$

UPDATE...Puma
SHORT TERM...50
LONG TERM...AGM
AVIATION...Puma