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679
FXUS63 KIND 221632
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1232 PM EDT Sun Sep 22 2024

.KEY MESSAGES...

- Widespread showers and thunderstorms today and this evening

- Turning cooler and more active with additional rain chances early
  next week

&&

.FORECAST UPDATE...
Issued at 944 AM EDT Sun Sep 22 2024

Clouds have increased from the west through the morning as rain with
embedded thunder slowly spreads into the Wabash Valley. Temperatures
at 13Z were generally in the upper 60s and lower 70s.

The ongoing forecast is in good shape for today with the focus for
the morning update on making subtle adjustments based on current
trends.

The main adjustment in the near term is to slow down eastward
expansion of the rain over the next few hours as lingering dry air
over eastern Indiana has aided in slowing down arrival times to
rain. That being said...with low pressure now over western Illinois
and a steady infusion of deeper moisture from the southwest...expect
rain showers to become numerous over the region through early
afternoon. Instability will be limited over much of the forecast
area with storms likely to be isolated. There is potential for a
subtle uptick in convection over the lower Wabash Valley by late day
where the airmass will be most unstable.

Highs ranging from the mid 70s to the lower 80s continue to look
reasonable with the increased cloud coverage and rain. Zone and grid
updates out.

&&

.SHORT TERM (Today and tonight)...
Issued at 303 AM EDT Sun Sep 22 2024

Beneficial rainfall is on the way to central Indiana starting late
this weekend as a frontal system takes aim on the Ohio Valley and
Great Lakes. MRMS reflectivity loop was showing large areas of
convection from Lake Michigan to the southern Plains near an
approaching cold front. Closer to home, IR satellite and obs were
showing only patches of AC over central Indiana. An associated warm
front extending from a low center over southeastern Wisconsin to the
upper Wabash Valley and northern Kentucky, was quiet early this
morning aided by upper ridging.

CAMs and Hi-Res models have showed a slowing trend regarding when
the upstream convection enters the Wabash Valley  with all but the
Wabash Valley now expected to stay dry overnight. However,
combination of synoptic forcing, weak instability and deep moisture
per Hi-Res soundings and max moving average PWATs to 2 inches per
SPC ILX sounding climatology, support widespread convection coverage
over central Indiana this morning over the Wabash Valley and
afternoon over areas near and east US-31. After the first wave moves
through, there may be a brief break, but more convection will fire
up late this afternoon and evening, closer to the front, as it moves
through from northwest to southeast tonight. With such deep
moisture, synoptic support and sufficient instability, the 90th
percentile DESI grand ensemble 24 hour QPF ending 12z Monday data
looks to have a better handle on things. Most locales should see a
quarter inch by Monday morning with 1 inch amounts amounts possible
in the most robust convection.

The increase in cloud cover and convection will limit temperatures
today. Many locales will not reach 80 degrees per DESI grand
ensemble 25th to 75th percentile 2m temperatures. That said,
overnight lows will only get down to the 60s due to increasing low
clouds and overall saturated boundary layer.

&&

.LONG TERM (Monday through Saturday)...
Issued at 303 AM EDT Sun Sep 22 2024

Guidance continues to advertise a much milder week across central
Indiana than in recent days, with highs in the 70s and lows in the
50s with the exception of Monday night, when southern areas may only
bottom out in the low 60s.

There is relatively high confidence in a solid rainfall early in the
work week - with chances highest Monday night into Tuesday.  Beyond
mid week, forecast confidence is minimal as run-to-run and model-to-
model inconsistencies and fluctuations continue with respect to the
overall pattern. The primary struggle is in the potential for the
larger scale upper trough to cut off from the main westerlies and
linger across the central or eastern CONUS, which could then
introduce the possibility of this large scale circulation also
absorbing potential tropical remnants as well.

Given these continued model struggles and uncertainties, can justify
no more than slight chance PoPs late week and into the weekend.

Continued expectation is for a broad inch or two of rainfall through
mid week, with uncertainty then very high beyond then. While this
may prevent further deterioration of the ongoing hydrologic
situation, it will not be enough to produce significant improvement
and certainly not enough to resolve the drought completely. At this
point, several inches of rain over multiple events will be needed to
get us back to baseline.

&&

.AVIATION (18Z TAF Issuance)...
-- Changed Discussion --
Issued at 1232 PM EDT Sun Sep 22 2024

Impacts:

- Rain with embedded convection at times this afternoon and evening
- Periodic MVFR ceilings through the afternoon...dropping to
widespread IFR ceilings overnight into Monday morning
- Patchy fog possible late tonight and early Monday

Discussion:

Rain has been slowly but steadily moving east across central Indiana
all morning and will continue to do so into the afternoon. Lightning
strikes so far have been minimal and over the next few hours appear
most likely to the east of the terminals moving further away into
Ohio. As low pressure tracks into lower Michigan late today and
pulls a cold front into the area...there is potential for renewed
convective development and at least a threat for a few thunderstorms.

The front will shift south through the area by late evening and
settle near the Ohio River for the overnight into Monday morning.
Should see showers diminish as a result with the focus transitioning
to lower ceilings and visibilities as moisture becomes trapped
within the boundary layer beneath an inversion. High likelihood of
IFR and lower ceilings developing at all of the terminals late
tonight with only modest improvement through midday Monday. Expect
visibilities to lower as well...perhaps down to 2-3SM at times.

Wind direction will remain chaotic through much of the forecast
period but should veer to a northerly direction in the post-frontal
environment then to north-northeast on Monday.
-- End Changed Discussion --

&&

.IND WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

UPDATE...Ryan
SHORT TERM...MK
LONG TERM...Nield
AVIATION...Ryan