IND issues Area Forecast Discussion (AFD) at Jun 25, 7:34 AM EDT243
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
Source:
IND issues Area Forecast Discussion (AFD) at Jun 25, 7:34 AM EDT---------------
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