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Forecast Discussion for Indianapolis, IN

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113
FXUS63 KIND 250137
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
937 PM EDT Wed Jul 24 2024

.KEY MESSAGES...

- Isolated thunderstorms overnight.

- Wildfire smoke at times which may reduce visibility and air
  quality

- Seasonable temperatures in the 80s through this weekend gradually
  warming to near 90 early next week.

- Dry late week weather will be replaced but warmer and unsettled
  weather by late weekend.

&&

.FORECAST UPDATE...
Issued at 936 PM EDT Wed Jul 24 2024

- Small overnight thunderstorm chances along and south of I-70
overnight
- Patchy Fog possible

Surface analysis late this evening shows a frontal boundary
stretched across Central Indiana, just south of I-70. The gust front
from earlier convection was  south of the IND forecast area.  Any of
the remaining shower/storm activity was found along or south of this
boundary. A few lingering showers/storms were found upstream over
Central IL.  High pressure was found over WI and MI. This high was
building its influence farther south into Indiana. Dew points across
Central Indiana remained rather humid, in the upper 60s to near 70.

Overnight the strong high pressure system to the north is expected
to continue a slow, southward sag across Indiana. Meanwhile, the
HRRR continues to suggest isolated thunderstorm redevelopment along
the frontal boundary early in the overnight night hours. Coverage
appears quite limited as energy arrives from IL. Thus will include
some small pops along the frontal boundary. Otherwise, dew point
depressions are suggested to fall to less than 2F at many spots.
This may result in some patchy fog. Isolated dense fog cannot be
ruled out. Ongoing lows in the low to middle 60s are on track.

&&

.SHORT TERM (This evening through Thursday)...
Issued at 257 PM EDT Wed Jul 24 2024

Scattered thunderstorms have developed across much of the area as of
2pm. One cluster of storms, which passed through the northern parts
of the CWA, is now exiting eastward into Ohio. A second cluster of
storms, currently just beyond the Illinois state line west of
Lafayette, is moving southeastward. Additionally, isolated to
scattered storms have popped up along the first cluster`s outflow
boundary and in the preceding air mass.

ACARS soundings out of IND show deep but fairly skinny CAPE
profiles. Lapse rates are steep near the surface, but become poor in
the mid to upper levels. Additionally, a lot of dry air is present
above 700mb. Updrafts have been shallower than the CAPE profile
would otherwise suggest. This is likely due to relatively weak
forcing and dry air entrainment. Hodographs are short, with the
fastest flow occurring above the EL and thus not likely to impact
storm organization. As such, storms should behave more or less like
single cells or multicell clusters today. Given the amount of dry
air, sufficient DCAPE (500-1000 J/Kg) exists for cold pool
generation. Any transient cold pools could allow for additional
storm-scale organization into a weak MCS.

As for convective hazards, strong gusty winds are the primary threat
today. As mentioned above, enough DCAPE is present for cold
downdrafts which may allow for brief downburst potential.
Furthermore, if a weak MCS manages to form then some enhancement
from rear inflow jets may allow for bowing segments/strong wind
gusts. Hail is possible, but as of right now updrafts may not become
vigorous or tall enough to support large (over 1 inch) stones.

Tonight, lingering showers and storms may occur as a cold front
slowly sags southward. This front should pass through within the few
hours around midnight. Drier flow from the northeast should take
hold, allowing for a clearing trend as we head into Thursday.
However, before this occurs, there may be enough time for patchy fog
to develop...especially south of the front. The front should help
clear out any lingering wildfire smoke as well. Highs on Thursday
will be cooler, but remain in the upper 70s to lower 80s which is a
touch below normal. An isolated shower across our far southern
counties is possible tomorrow, though this is conditional on how
quickly the front exits the area.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 257 PM EDT Wed Jul 24 2024

Thursday night through Saturday morning...

The long term will start off with the cold front well south of the
area as high pressure builds in across the Great Lakes and a ridge
builds over the nation`s mid section. Subsidence associated with the
high along with a dry column per model soundings supports dry
weather through at least midday Saturday. ENE winds around the high
will result in comfortable humidity levels, although little cloud
cover will still allow temperatures to come close to seasonable
afternoon highs in the middle 80s. Meanwhile, dew points mostly in
the upper 50s and lower 60s a good radiational cooling setup will
mean overnight lows will mostly be in the upper 50s to lower 60s.

The surface high will shift to the Appalachians by late Saturday.
This will allow for Gulf moisture to build over the Ohio Valley.
With this in mind and an approaching Plains upper trough, would not
rule out a thunderstorm or two over far southwestern parts of
central Indiana Saturday afternoon and evening. That said,
confidence in convection is low with the trough still a bit to the
southwest of the area.

Saturday night through Wednesday...

Gulf inflow will continue late in the weekend and into next week.
Meanwhile, an upper low pressure system will move from the Plains
into the Great Lakes late Sunday and Sunday night. Another upper
wave is expected to move across the lower Great Lakes toward the
middle of next week. The combination of increasing humidity and
instability along with upper support will lead to a return of warmer
temperatures and thunderstorm chances. Confidence in timing of the
greatest coverage is not great but current indications suggest
Monday into Tuesday would be the best time frame. 40-60% PoPs look
reasonable then. That said, there are signals that central Indiana
could be in the path of potential ridge riders, especially Wednesday
as the upper flow becomes more northwesterly as a dome of high
pressure expands north across the Plains.

Some locales could reach the lower 90s next week as the southerly
low level flow continues and the nearest cold front likely remains
northwest of the area.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 727 PM EDT Wed Jul 24 2024

Impacts

- Thunderstorms exiting the area along with isolated MVFR Cigs.
- VFR Conditions return by 250200Z.
- MVFR fog possible overnight at LAF/HUF and BMG.

Discussion:

A cold front over Central Indiana was pushing south of the TAF sites
near 00Z. Radar shows decaying thunderstorms over central Indiana as
the advancing gust front has cut off access from the most favorable
air for TSRA development. Thus the decaying TSRA may be present at
BMG and IND for the first hour or so of the TAF period.

Thereafter, high pressure over the upper midwest will sag southward
into Indiana, providing mainly dry weather for Indiana tonight and
Thursday. HRRR suggests some TSRA redevelopment near HUF and the
lingering frontal boundary, but confidence is low for this and have
only included a VCTS mention for the moment.

High thin cloud is mentioned on Thursday due to possibly continued
smoke aloft, creating a thin veil.


&&

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

$$

UPDATE...Puma
SHORT TERM...Eckhoff
LONG TERM...MK
AVIATION...Puma

Previous Forecast Discussions may be found at
NWS Indianapolis, IN (IND) Office Forecast Discussions.
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