Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/08/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 1015 PM EDT Sun May 7 2023

.Forecast Update...
Issued at 1015 PM EDT Sun May 7 2023

Generally quiet weather across the CWA this evening with the
exception of a stray thunderstorm just north of Kokomo. This cell
appears to be tied to a weak cold front slowly sagging southward.
Convection ignited along the majority of the boundary in northern
Indiana earlier but has been on a weakening trend. Recent ACARS
soundings out of IND, which is south of the boundary, show
stabilization in the lower boundary layer. This may be why the
convection has been slowly weakening as it drifts south.
Nevertheless, some gusty winds or small hail is possible in any
lingering storm as plenty of CAPE and strong flow remain aloft.
Though based on trends this should not last too much longer.

A much more impressive area of convection is noted northwest into
Illinois. Most CAM guidance depicts this congealing into an MCS and
heading southeast towards Indiana. However, a few things are working
against it. This morning`s convection has stabilized the atmosphere
ahead of an effective warm front / residual outflow boundary that
extends northwest to southeast near the Illinois Missouri border. In
fact, convection has been rather robust along this boundary for much
of the day today with numerous severe weather reports.

While some rouge storms have attempted to drift eastward away from
the warm front into the convectively modified air mass, they quickly
lost steam and subsequently dissipated. This poses the question as
to whether tonight`s developing MCS will meet the same fate. A
reasonable guess would be to assume that this feature turns
increasingly southward in search of instability. SPC mesoanalysis
show a theta-e and CAPE gradient extends along the effective warm
front. This could gradually lift northward as the night goes on,
which will need to be watched as it could end up being the most
likely path overnight convection takes.

&&

.Short Term...(This evening through Monday)
Issued at 259 PM EDT Sun May 7 2023

This afternoon temperatures across central Indiana range from the
upper 70s north where there`s been plentiful sunshine to the middle
to upper 60s south where clouds from convective blowoff have been in
abundance. Central Indiana is currently dry with convection to the
south and more firing off to the west over southern Illinois.

The main forecast concern will be rain and thunderstorm chances and
timing, but unfortunately confidence in timing/placement of
convective chances during the short term remains low, with varying
solutions for potential MCS development. Could see some of the
storms firing over southern/central Illinois move into the
southwestern counties early this evening, but they may also dive
more southeast toward the better instability. With weak upper
forcing, could see development later tonight in Iowas/northwest
Illinois that could then ride the ridge and theta-e gradient down
into northwestern Indiana and head southeast from there, and this
is the prevailing thought that went into the forecast Pops. This
could also hold off or stay north of the area and instead drop an
outflow boundary that could fire late Monday morning/early Monday
afternoon. Any severe threat will be contingent on available
instability and local boundaries. Abundant moisture could lead to
heavy rainfall in storms, and any that move over already saturated
areas or get tied to a local boundary could pose a localized
flash flooding threat.

Warm advection and potential for some cloud cover overnight should
keep lows in the upper 50s to lower 60s. Temperatures Monday could
be suppressed due to cloud cover from any ongoing MCS or debris
clouds from nearby MCS, so even with warm air over the area only
looking at highs in the 70s.

&&

.Long Term...(Monday night through Sunday)
Issued at 259 PM EDT Sun May 7 2023

Monday night...

A cold front will be moving through at the start of the
period with numerous showers and storms expected ahead of the
boundary. Moderate instability and effective bulk wind shear around
35-45 kts will support the potential for some organized
thunderstorms. A few of these could be strong to severe, but this
will be heavily dependent on how convection evolves during the day
Monday. Confidence remains low due to the low-predictability pattern
in the short term period. The cold front should move south of the
area by late Monday night with mostly quiet conditions expected.
Look for slightly cooler lows in the 50s as cold air advection
filters in.

Tuesday through Wednesday night...

Increasing subsidence from surface high pressure settling in will
lead to quiet conditions with plentiful sunshine. There is a non-
zero chance for an isolated light shower or two with lingering low-
level moisture on Tuesday, but confidence is very low. Otherwise,
expect pleasant weather with highs in the 70s and dewpoints dropping
into the 40s.

Thursday through Sunday...

More active weather is expected late week as surface high pressure
moves east. Return flow between the surface high pressure to the
east and a developing surface low over the plains will advect warm-
moist unstable air northward. Dry weather is likely for much of the
day Thursday, but a warm front lifting north late will lead to
increasing rain chances. Scattered showers and storms will be
possible at times from late Thursday through Sunday as central
Indiana remains in a warm-moist unstable airmass. Much of this will
be diurnally driven with the best chances for storms in the
afternoon, but a cold front is expected to move through late Sunday.

Temperatures will be above average during the latter half of the
period with highs generally in the upper 70s to low 80s.

&&

.Aviation...(00Z TAF Issuance)
Issued at 745 PM EDT Sun May 7 2023

Impacts:

* Thunderstorm chances return overnight
* MVFR ceilings move in from the northwest near daybreak
* Shifting wind direction with a front and boundaries meandering
  about

Discussion:

A rather complicated forecast tonight as much of the impacts will be
determined by convective evolution upstream. Nevertheless, VFR
conditions are expected through much of the night as thunderstorms
arrive rather late...by around 10z from HUF to LAF. These storms
should progress southeastward reaching IND and BMG by 12z. Timing
is a bit tricky, but these times represent the best idea based on
current information. Winds will generally retain a southerly
component, though any thunderstorm will briefly change the wind
direction and or increase the gust speed. After the main batch of
storms enters the region, lowering ceilings are expected with
possible MVFR conditions by daybreak. Once the convection is
through, expect improving conditions. Renewed shower and
thunderstorm activity is possible tomorrow afternoon, but details
on this are largely dependent on how tonight`s convection evolves.
Overall, a rather low confidence forecast going forward.


&&

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

&&

$$

Update...Eckhoff
Short Term...CP
Long Term...Melo
Aviation...Eckhoff