147
FXUS63 KIWX 241000
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
600 AM EDT Mon Jun 24 2024

.KEY MESSAGES...

- Seasonable temperatures and low humidity values today with
  dry weather persisting.

- Chance of storms increase overnight tonight with some
  potential of thunderstorm wind gusts over 40 mph.

- Scattered thunderstorms are possible Tuesday with some potential
  of strong to severe thunderstorms Tuesday and Tuesday night.
  Confidence remains low in timing and the extent of the severe
  weather threat.

- If lesser storm coverage/cloud cover is realized for Tuesday,
  heat indices may approach the upper 90s to around 100 Tuesday
  afternoon across portions of the area.

&&

.DISCUSSION...
Issued at 335 AM EDT Mon Jun 24 2024

Main theme of previous forecast remains intact. A quiet Monday
will be followed by building heat and humidity for Tuesday, but
the extent of this heat and humidity will depend on thunderstorm
and cloud evolution late tonight into Tuesday. There is a
potential of strong to severe storms late tonight into Tuesday
night, but the extent of this threat and timing greatest chances
remains low confidence.

In the near term, a small scale but compact upper level short wave
continues to drop across southeast Lower Michigan. A small pocket of
500 J/kg MUCAPE did allow maintenance of isolated thunderstorms
across central Lower MI, but this line has weakened as it has
approached south central Lower Michigan. A few showers and
sprinkles can be expected over next few hours across southern
Lower Michigan.

Otherwise today should be a quiet, pleasant day with seasonable high
temperatures and weak winds under the influence of low level
anticyclone. Low level thermal trough will be positioned across the
area with a dry air mass in place and afternoon dew points likely
mixing out into the mid 50s in many spots.

For tonight, highly progressive pattern allows for quick
rebound in mid level heights across the western Great Lakes with
a strong low level jet developing from the Central Plains into
Minnesota. Strong low level mass/moisture convergence at the
nose of this jet should force one or two convective systems
tonight across the Upper Midwest. Evolution of mid and upper
level pattern will allow a very strong low-mid level theta-e
gradient to push into the region overnight. Some concern for MCS
activity tonight given this strong instability gradient across
the region and eastward shifting strong mid level lapse rates.
In addition, the development of the strong low level jet across
the MS Valley will result in north to south Corfidi vectors
tonight and a southward preference to MCS propagation from the
Upper Midwest. Given this low level jet interaction with
outflows and stronger instability back across the Corn Belt,
would suspect the upwind propagation idea among many of the
HREF members would be preferred as opposed to forward
propagation. This would put local area in possible path of a
potential upstream MCS late tonight into Tuesday morning. As is
the case in these type of setups, difficult to have much
confidence in exactly where potential convective system
initiates tonight and where it will track. Late arrival (low
level CIN) and weaker deep layer shear with southward extent
across the southern Great Lakes and Ohio Valley, may allow for
lesser severe threat locally with a Marginal Day 1 Risk for
western two thirds of the area late tonight. One caveat is these
convective disturbances have localized stronger shear
environments and if well developed cold pool can develop, cannot
discount some potential of severe thunderstorm wind gusts
overnight into early Tuesday.

Forecast confidence further dwindles for Tuesday with a high amount
of dependence on how potential AM storms/outflow boundaries set up
during the day. The potential does exist for an outflow
boundary to lay out across the area from these storms which
could be possible focal point for more storm development in the
afternoon. The environment Tuesday afternoon could be
characterized by moderate to strong instability, but guidance
consensus suggests shear magnitudes decrease through the
afternoon without a well defined synoptic scale disturbance to
latch onto. If stronger overnight convection develops tonight,
outflow boundary could be pushed farther south with lower
thunderstorm potential Tuesday afternoon/early evening. The
uncertainty in convective forecast results in low confidence in
extent of heat indices Tuesday afternoon. Overall trend may be
to slightly lower confidence in advisory level heat indices with
a suspicion that outflow boundary/remnant cloud cover could be
limiting factor. Opted for middle of road solution given all the
uncertainties with peak afternoon heat indices from lower 90s
north to mid-upper 90s south on Tuesday.

For Tuesday night, thunderstorms chances will likely become renewed
as low amplitude upstream short wave approaches from the west
interacting with what should be rich west-east oriented low
level theta-e ridge. These storm chances may continue through
the night into early Wednesday across the south as low level
convergence axis shifts southward. Still feel that better focus
for stronger storms Wednesday afternoon may end up just south of
the area with outflows pushing effective boundary south of the
area.

Cooler and less humid conditions build in for Thursday, but the
highly progressive nature of this pattern will allow for highs back
into the mid 80s to around 90 by Saturday. Another potential frontal
passage Saturday would bring more chances of showers and storms for
first part of weekend, but timing of this fropa will need to be
resolved over next several forecast cycles.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 556 AM EDT Mon Jun 24 2024

Tranquil weather within the critical TAF period thanks to high
pressure in place. This high pressure gives way to shortwave
aloft and the risk of showers and storms approaching KSBN in
the latter portion of the TAF period. Confidence is medium at
best. The anticipated line of storms is forecast to develop over
the MN/WI line very late this afternoon and dive ESE.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Marsili
AVIATION...Brown