967
FXUS63 KIND 300038
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
838 PM EDT Sat Jun 29 2024

.KEY MESSAGES...

- Severe Thunderstorms possible this Evening
- Cooler Sunday and Monday, heat returns on Tuesday and Wednesday
- Rain/storm chances return Wednesday onward

&&

.FORECAST UPDATE...

...Strong to Severe Thunderstorms Possible the Remainder of the
Evening...

Latest mesoscale analysis was showing CAPES to 4000 J/kg over the
Wabash Valley with lesser CAPE over east central sections, closer to
where the bowing line went through late this afternoon. Radar  was
showing widely scattered thunderstorms from south central Indiana
into the Wabash Valley, closer to the outflow from the earlier
convection. Meanwhile, a cold front extended from near the
northeaster Indiana and southern lower Michigan border to around
Rensselaer and points southwest. This front will move to the I-70
corridor late this evening and south central Indiana overnight. The
front will interact with the strong, albeit weakening instability
and 70+ degree dew points to trigger more convection. Marginal shear
but strong instability suggests a few severe storms will be possible
with damaging winds the main concern.

The thunderstorms should move to the southeast of the area toward
morning as the front clears and much drier air moves in. This will
also allow for clearing northwest to southeast and cooler
temperatures with lows in the lower 60s northwest to around 70
southeast looking good. The northwest post frontal winds should keep
fog from being an issue.

&&

.MESOSCALE UPDATE...
Issued at 603 PM EDT Sat Jun 29 2024

The bowing line of thunderstorms that produced some damaging winds
along its path has moved southeast of central Indiana. Meanwhile
more isolated benign cells were forming over the Wabash Valley and
east central Illinois as well as further north, closer to the
synoptic cold front that was extending from near South Bend
southwest to Kankakee. The atmosphere has recovered in a big way
over east central Illinois into north central Indiana, ahead of the
front with CAPEs to 4500 J/kg. Meanwhile, further southeast along
the bowling line path, CAPEs have dropped below 1000 J/kg and CIN
has resulted. So, think the Wabash Valley activity will not be a
huge concern moving into a more worked over atmosphere. However,
convection may light up along and ahead of the front and be at least
a semi-concern later this evening as the front gets closer.

&&

.SHORT TERM (Today and tonight)...
Issued at 146 AM EDT Sat Jun 29 2024

Forcing for ascent this morning is primary from warm/moist
advection preceding a low amplitude shortwave trough upstream. The
effects of the shortwave itself are otherwise minimal on our
atmosphere at this latitude. These are difficult patterns to
forecast precision with regards to timing of convection.

Current thinking is the anomalous moisture plume at both low levels
and aloft will continue supporting scattered to numerous showers,
and modest instability will support isolated thunder. A small
midlevel vorticity maxima likely augmented by ongoing convection in
Missouri may result in an uptick in convective coverage early this
morning as it moves east and interacts with deeper moisture plume.
In fact, some new convection and lightning strikes are occurring as
of this writing in west-central Illinois. This will probably expand
and reach Indiana around daybreak.

There will probably be a decrease in coverage and intensity by late
morning or midday as the core of the low level jet and moisture
plume shifts eastward. Diurnal convection may increase ahead of the
front late afternoon into the evening. CAPE/shear parameter space
may be marginally supportive of a few strong to severe wind gusts.
This should mean a relative minimum in convective coverage during
the early-mid afternoon time frame.

Temperatures should be similar to yesterday but richer influx of
moisture will result in noticeably more humid conditions. As the low-
amplitude shortwave trough passes, it will nudge a drier continental
air mass in overnight along with modest cold advection bringing
temperatures down slightly compared to previous nights.

&&

.LONG TERM (Sunday through Friday)...
Issued at 146 AM EDT Sat Jun 29 2024

Sunday and Monday...

The low amplitude meridional pattern will continue through the long
term. Initially, this will lead to cool, calm conditions with surface
high pressure and upper level troughing for Sunday and Monday, and
should allow for generally clear skies and highs around 80. Winds
will veer post frontal passage today and continue to be northerly to
northwesterly through Monday.

With mostly clear skies and dew points in the 40s, overnight lows
should be well below normal for both Sunday and Monday night.
Current forecast is for lows in the 40s each night.

Tuesday through Friday...

The next phase of the this pattern will arrive mid week, with broad
ridging developing aloft. By Tuesday, 850mb temps rise by about 5-10
degrees, which under full sun and efficient mixing corresponds to
highs in the mid to upper 80s. The primary axis of warm air will
then arrive Wednesday, with highs expected to be back into the 90s.
This upper ridge will continue to remain aloft keeping temperatures
above normal through the end of next week.

Even though upper level ridging will be in place across the Ohio
Valley, precipitation chances will still increase as a succession of
weak waves develop within broad upper level diffluence in the right
entrance region of the upper jet. This should lead to variable
thunderstorm chances Wednesday through Friday, until a frontal
boundary moves through late week, decreasing surface moisture.

Its still too early to pinpoint specifics regarding timing and
potency of thunderstorms Wednesday through Friday of next week.
Ensemble guidance is highly variable on how the low level
disturbances develop and pass through the Ohio Valley, of which will
greatly influence surface conditions over central Indiana. For now,
understand and prepare for thunderstorms to potentially interrupt
holiday plans next week, and stay alert for updates as forecast
confidence increases over the next several days.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 625 PM EDT Sat Jun 29 2024

Impacts:

- Thunderstorms and brief MVFR flying conditions possible through
  04z

Discussion:

The cold front will slide southeast to near a KIND to KHUF line at
00z and then to near the Ohio River by 06z. Until the cold front
moves through, a moist, unstable atmosphere and lift from the front
and smaller scale boundaries will result in scattered thunderstorms.
Would not rule out a strong or severe thunderstorm but with
coverage expected to be 30% and less, only went with VCTS.

The rest of the TAF period looks good with NW winds bringing in
drier and cooler air which will present as clearing skies and
northwest winds less than 10 knots tonight and near or more than 10
knots Sunday afternoon.


&&

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

$$

UPDATE...MK
SHORT TERM...BRB
LONG TERM...Updike
AVIATION...MK