243 
FXUS63 KIND 251134
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
734 AM EDT Tue Jun 25 2024

.KEY MESSAGES...

- Thunderstorms will be around at times today into Wednesday. Some
  severe storms are possible, especially this afternoon. 
- A good amount of uncertainty remains in the specifics of the storm
  chances today into tonight.
- Today will likely be the warmest day of the week.
- A brief respite from heat and humidity Thursday before another 
  warm up and additional storm chances this weekend.

&&

.MESOSCALE UPDATE...
Issued at 734 AM EDT Tue Jun 25 2024

A single storm has entered our CWA from the northwest, and has 
prompted a few warnings so far. The cell appears to be a multicell 
cluster, and has been quite pulsey in nature. SPC mesoanalysis shows 
a tight CAPE gradient stretching from South Bend Indiana 
southwestward to Vincennes, with higher CAPE values with westward 
extent. This area of instability is advecting into Indiana on the 
southern edge of a potent low-level jet (40-50kt across northern 
Indiana). 

ACARS soundings out of Indianapolis show a modest CAPE profile aloft 
from about 700mb, with a lot of dry air and a stout inversion below. 
ACARS soundings further west out of Peoria IL, deeper into the area 
of instability, show a much larger and deeper CAPE profile. MUCAPE 
over 2500 J/Kg is observed (versus less than 1000 J/Kg in Indy). 
Additionally, both soundings show an inversion in the lower levels, 
so the storm is elevated and rooted roughly around 850mb.

Going forward, the storm should experience gradual weakening as the 
low-level jet that's feeding it slowly diminishes as diurnal mixing 
picks up. However, a few updraft pulses capable of large (up to 1 
inch) hail and gusty winds (up to 60mph) are possible in the near-
term before the cluster finally dissipates. It is likely that the 
storm persists only for another hour, if that.

Just a quick note, another storm complex is located across northern 
Illinois into lower Michigan, and is propagating southward into the 
low-level jet. This system has an established cold pool, which will 
likely increase its longevity compared to the storm cluster 
currently in our area. CAMs will not handle this situation well. We 
are watching this closely, and will provide update AFDs/mesoscale 
AFDs as needed through the morning and into the early afternoon.

&&

.SHORT TERM (Today and tonight)...
Issued at 302 AM EDT Tue Jun 25 2024

Forecast remains challenging for the short term, as details will be 
mesoscale driven. Each potential cluster of thunderstorms may impact 
future ones, which results in a low confidence forecast with 
multiple potential outcomes. CAMs often struggle with weakly forced 
scenarios, so use caution in using individual CAM output.

Bottom line: There will be chances for thunderstorms throughout the 
short term, some of which could be strong to severe this afternoon 
depending on available instability. Hot temperatures will return, 
but how hot depends on convective development.

Early this morning...

An area of thunderstorms had developed across northeast Illinois, on 
a temperatures/moisture gradient along an approaching airmass. The 
storms were moving south/southeast along the gradient. As the 
airmass works its way east during the early morning, these storms 
should begin to move east as well. Stronger winds aloft remain 
across northern portions of the area, so the storms should hang on 
longest there. 

Uncertainty remains though on the speed that the area of storms 
moves east. Will have some chance PoPs, mainly across the northern 
forecast area for now.

Today...

The temperature gradient aloft should be east of central Indiana by 
the start of the today period, but some warm advection will still be 
ongoing. There will likely be some clouds around from the earlier 
convection, and some of this convection may still be ongoing, but in 
a weakened state.

Meanwhile, the tail of some additional upper forcing currently 
creating storms across Wisconsin, will be moving into Indiana from 
the north. Whether it can generate more convection will depend in 
part on what the early morning convection does. More early 
convection/clouds will lead to lower odds of convection with this 
forcing and vice-versa.

There are multiple scenarios that may play out, but feel that these 
two are the most likely:

1) Clouds/dying early morning convection inhibits additional 
development for a while today. Afternoon convection develops along 
old outflows and any upper forcing that moves in. Mainly scattered 
storm coverage. 

2) Clouds/early morning convection dissipate quickly. Instability 
builds and a line of storms moves south across the area from the 
initial upper forcing. These storms will intensify during the late 
morning into the afternoon as they move south across the area. 
Scattered to numerous coverage would occur.

Either scenario could result in strong to severe storms in the 
afternoon given the potential instability that could build. The 
primary threat would be damaging winds.

Will keep PoPs in the chance category given the high uncertainty.

The other concern today will be the heat. 850mb temperatures will be 
above 20 degrees C, leading to the potential of mid and upper 90s. 
Dewpoints will be around 70 to the lower 70s, leading to potential 
heat indices near 105 in the southwest forecast area. 

If confidence were higher in cloud cover/convection, a Heat Advisory 
would be needed in the far southwest. However, uncertainty is much 
too high. May issue a Special Weather Statement for heat. 

Tonight...

Thunderstorm chances will continue tonight. Storms may be ongoing 
early in the period from the afternoon convection, depending on its 
eventual timing.

Overnight, a cold front will approach from the north, along with 
some additional upper energy. This will result in more shower and 
thunderstorm development, especially north. However, once again, 
uncertainty remains on the amount of instability that will be 
available due to earlier convection.

Will go with high chance category or likely category PoPs tonight, 
with highest PoPs overnight when the cold front approaches. Low 
temperatures will be from around 70 to the lower 70s.

&&

.LONG TERM (Wednesday through Monday)...
Issued at 302 AM EDT Tue Jun 25 2024

The long term period will see temperatures fluctuating between near 
normal and above normal with multiple chances for showers and storms 
as numerous system pass through the region. 

Wednesday morning will start off with showers and thunderstorms 
along a cold front pushing south/ southeast through the area. As 
this will be an outflow influened frontal environment, can't rule 
out the possibility of a few stronger cells forming and potentially 
producing damaging winds and maybe some hail as the front exits. 
There is some uncertainty on when rain will end as some models 
indicate redevelopment could occur in the evening to overnight 
hours. Overall, expecting a bulk of the rain to come to an end by 
the evening to early overnight hours Wednesday.

Behind the front, cooler temperatures and high surface pressure will 
move in allowing for a pleasant and relatively dry day Thursday. 
Unfortuneatly, this nice weather will be short lived as heat and 
humidity return for the weekend. The end of the long term period 
will see multiple chances for precipitation but models lack 
agreement on exact extent and timing. Currently best precip chances 
look to be Saturday, but could arrive as early as late Friday. This 
will likely be followed by a dry break before another system 
potentially arrives around Tuesday.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 646 AM EDT Tue Jun 25 2024

Impacts: 

- Isolated convection this morning, then chances for convection
  anytime thereafter.
- Wind gusts over 20kt mid morning through the afternoon

Discussion: 

Low confidence forecast due to high uncertainty in convective 
development through tonight, as each round of convection will have 
an impact on the next. 

Isolated storm west of KLAF near 11Z will continue to slowly move 
southeast. It may not make it to KIND as atmosphere is less 
favorable there. Other storms will develop/move in later this 
morning or early afternoon north and eventually move south. More 
storms will develop tonight.

Given the low confidence, continued with VC or PROB30 at all sites. 
Outside of convection, VFR conditions are expected.


&&

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

&&

$$

MESOSCALE...Eckhoff
SHORT TERM...50
LONG TERM...KF
AVIATION...50