Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/27/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 951 PM EDT Wed Jul 26 2023

.Forecast Update...
Issued at 951 PM EDT Wed Jul 26 2023

Central Indiana remains quiet this evening, with just some clouds
around. Thunderstorms continued across northern Indiana near the
tail of a shortwave. Plentiful instability remains across central
Indiana, but convective inhibition continues as well.

Some decoupling of the boundary layer has occurred as can be seen
with the loss of wind gusts across the area. ACARS soundings continue
to show an inversion aloft over the area.

As the shortwave continues to move east, the thunderstorms across
northern Indiana should continue their trek southeast. These could
reach the northeastern forecast area early in the overnight. Severe
threat looks marginal. There could be some marginally severe hail or
an isolated severe gust if something can punch through to the
ground, especially northeast.

Adjusted PoPs to reflect this thinking, with chance PoPs mainly
northeast and slight chance PoPs elsewhere. Adjusted sky as
necessary based on trends seen on satellite. Temperatures look
reasonable so just made some tweaks.

&&

.Short Term...(This evening through Thursday)
Issued at 104 PM EDT Wed Jul 26 2023

...Strong to potentially severe storms this evening and tonight...

Rest of Today.

As of early this afternoon, a broken and skinny line of convection
has marched across central Indiana bring a brief cooldown of 4-8
degrees and leaving behind an area of fairly widespread cloud cover.
Further to the west, the southern periphery of the more intense
storms across Chicago and northern Indiana continues to generate
light to briefly moderate rain with additional cloud cover. This
will further limit heating through the afternoon and evening hours
and favors the scenario 1 outcome that has highlighted in
yesterday`s AFD. Model and ACARs soundings both show a weak cap at
the top of the boundary layer which is further limiting the upscale
growth of the ongoing convection. Expectations are for the mid
afternoon to be dominated by the scattered showers associated with
storms to the north with any severe weather during the late evening
into overnight hours. Further thoughts on the severe potential will
be discussed below and any mesoscale discussions above.

Tonight.

With the lack of more robust diurnal heating, intense convection
looks to hold off until after 00Z when the weak surface front
approaches the northwestern counties.  Models continue to weaken the
strength of the front with the front likely only barely making it
into the forecast area.  This should be enough though to kick off
isolated to scattered thunderstorms with marginally severe hail.
Models have struggled to capture even ongoing convection, so will
not trust their output later into the overnight. Model soundings by
the early overnight show upwards of 2500 J/kg of elevated
instability with much of that situated above the freezing level
which further will enhance the hail threat.  Damaging winds are
possible if storms end up more organized than expected, but a near
surface inversion will limit the threat. Convection will gradually
lessen in coverage later into the overnight hours as the better
forcing aloft pushes further east into eastern Michigan.

Thursday.

Primary focus for tomorrow will be on the increasing heat threat
along with a conditional threat for a few afternoon thunderstorms.
By the morning hours, any overnight convection should have come to
an end with model soundings showing clearing skies across central
Indiana. Convective temperatures should be met by the late afternoon
hours which will allow for a cu field to form.  An outflow boundary
from overnight convection may be just strong enough to break the
weak cap that is expected which would allow a thin line of
convection to form.  Confidence on this is low and would be
dependent on a well defined boundary to be formed by tonight`s
convection. Temperatures should reach into the mid 90s for much of
the area, but don`t have the confidence to go into the upper 90s as
some models like the GFS show with the expected cu formation and
shower potential. Will continue the Heat Advisory but not thinking
that an upgrade to Excessive Heat Warning is needed at this time.

&&

.Long Term...(Thursday night through Wednesday)
Issued at 104 PM EDT Wed Jul 26 2023

-Dangerous heat expected Friday.

Thursday Night through Saturday.

Quiet but very warm conditions will continue through the overnight
hours Thursday night with lows only falling into the mid to upper
70s due to the increased surface moisture limiting the radiational
cooling even with mostly clear skies.  The hottest day of the week
is expected for Friday with highs near 100 in spots, but think that
may still also be a bit overdone.  Dewpoints should remain steady in
the low to mid 70s with little mixing expected. Heat indices above
105 look very likely with the potential for a few spots to reach 110
which may warrant an excessive heat warning.  Will collaborate with
neighbors on any potential headline later this afternoon and again
as confidence on how high the dewpoints will be increases.

Convection is then expected across the Great Lakes region Friday
night into Saturday which should bring at least some relief to the
heat to central Indiana even if the precipitation stays to the
north. Thoughts are that outflow boundaries should be able to
initiate storms across central Indiana during the daytime hours, but
confidence isn`t quite as high as it is for the overnight storms to
the north.

Sunday Through Wednesday.

Northwesterly flow aloft becomes more predominant Sunday with the
ridge amplifying across the Central Plains which will bring some
relief to the heat but more importantly an improvement in surface
dewpoints which will fall into the 60s and briefly even upper 50s.
Storm complexes along the ridge look likely Sunday night through the
early week, but confidence on location and strength remains low.
Best chances for an MCS currently look to be Monday into Tuesday.
Other than organized convection, rain chances will be low with
seasonable temperatures and humidity through the early work week.

&&

.Aviation...(00Z TAF Issuance)
Issued at 656 PM EDT Wed Jul 26 2023

Impacts:

* Isolated to scattered convection possible through about 05Z.
* Wind gusts up to around 25kt mainly before 03Z.
* Patchy fog possible at KLAF mainly near sunrise.

Discussion:

Weak forcing for convection will continue this evening, with main
forcing off well to the north. Will watch a boundary moving across
northeast Illinois, but at the moment expect low coverage of
convection this evening. Best chances for TS will be at KLAF/KHUF,
so will mention VCTS there. Elsewhere will just mention showers.

Some fog may form at KLAF near sunrise, otherwise expect VFR
conditions into Thursday.

Some LLWS is possible overnight, but core of stronger winds aloft
will be east of the sites.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 8 AM Thursday to midnight EDT Friday night
for INZ021-028>031-035>049-051>057-060>065-067>072.

&&

$$

Update...50
Short Term...White
Long Term...White
Aviation...50