761
FXUS63 KIWX 221723
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
123 PM EDT Sat Jun 22 2024

.KEY MESSAGES...

* Dangerous heat continues today and becoming breezy, but relief
  from the heat arrives for Sunday and Monday.

* Showers and scattered storms expected to move in tonight with some
  potential of wind gusts in excess of 50 mph late evening into
  early overnight hours.

* Depending on evolution of clouds and storms on Tuesday, heat
  indices may reach closer to 100 degrees again Tuesday
  afternoon.

&&

.DISCUSSION...
Issued at 350 AM EDT Sat Jun 22 2024

No changes will be made to ongoing heat headlines, with one more day
of peak afternoon heat indices in the 95 to 100 degree range.  Some
potential of gusty thunderstorms tonight, particularly northwest
Indiana into southwest Lower Michigan. Heat may make brief return
for Tuesday with additional thunderstorm chances for Tue-Wed.

Primarily dry weather is expected today, but will be monitoring a
cluster of showers and thunderstorms moving out of northern
Illinois/southern Wisconsin this morning. This area of storms
appears to be tied to some broad low level theta-e advection and
perhaps earlier enhanced by some anvil seeding from upstream Corn
Belt convection. Bulk of these showers and thunderstorms should
bypass the local area to the northwest following progression of
pocket of 500-1000 J/kg MUCAPEs from southeast Wisconsin into
west central Lower Michigan. Otherwise, still expecting today to
be dry as weak mid level troughing swings northeast across
central Lake Michigan with a robust +9 to +11 C 700 mb thermal
ridge nosing into southern Lower Michigan. Weak cyclogenesis
across WI today will allow for respectable strength to low level
height gradient across the Great Lakes and Ohio Valley. Mixing
up to 850-800 mb should allow for some peak afternoon gusts into
the 20 to 30 mph range. This good mixing should result in dew
points being held in check in the 60s for most areas similar to
yesterday. The combination of high temperatures in the low to
mid 90s and these modest dew points should result in another day
of peak afternoon heat indices between 95 and 100 degrees.

For late this afternoon into this evening, a stronger upper level
trough will race east out of the eastern Dakotas allowing for cold
frontal progression into northwest IL/southeast WI by late evening.
Showers and storms should fill in along or just in advance of the
front in pre-frontal moisture pooling zone early this evening. All
indications still point to a sharp gradient in convective
environment from western Great Lakes to the southern Great
Lakes/Ohio Valley with best instability axis remaining from northern
IL into southeast WI. Dampening of the mid/upper level ridge
later today will allow some modest deep layer shear values into
the 25 to 30 knot range by this evening across far northern
Indiana/southern Lower Michigan. However, convective line will
have less downstream instability to work with across the local
area late evening/early overnight, and given marginal shear
profiles, should see a transition to outflow dominant line. SPC
Day 1 severe probs have been increased across the area with a
Slight Risk across the far northwest. Still feel that
thunderstorm wind gusts in the 35 to 50 mph range will be of
higher confidence with this convective line, with some lower
confidence in isolated severe gusts. Best chance of near
severe/severe wind gusts should be in a fairly narrow temporal
window in the 04-07Z timeframe from northwest IN into perhaps
far SW Lower Michigan. The convective line should gradually wane
with time during the overnight hours tonight.

A few storms are possible into Sunday with cold frontal progression
across the area, but effective sharper convergence zone resulting
from outflow evolution may be focused just southeast of the area.
Less humid conditions will overspread the area behind this
front Sunday afternoon into Monday.

Monday will be a transition day and appears to feature pleasant
conditions with seasonable temperatures and low humidity levels. A
progressive northern stream pattern will allow for a quick
transition to a dampening of incoming upper level ridge Monday
night/early Tuesday and a period of very strong return positive
low/mid level theta-e advection late Monday night into Tuesday.
Forecast soundings still suggest capping may hold into midday
Tuesday, but elevated moisture return could be enough for
isolated-scattered storms moving in from the west late Monday
night into Tuesday morning across the west. While current
indications still suggest a potentially more active convective
pattern Tuesday afternoon into Wednesday, forecast confidence in
details remains low given lead forcing on Tuesday will be
driven largely by upstream diabatic processes across the Upper
Midwest, and the fact that stronger synoptic forcing lags
across US/Canadian border later Tuesday night into Wednesday.
This pattern may support MCS activity, but mesoscale details
including instability magnitudes and shear magnitudes with
southward extent across local area will need to be resolved in
later forecasts. Depending on how clouds/convection play out
Tuesday, a brief return of heat indices from the mid 90s to
around 100 is possible Tuesday afternoon.

Chances of storms may persist with cold frontal progression into
Wednesday, but quieter and cooler weather spreads back into the area
for Thursday. Temps should warm to above normal again for Fri-Sat,
but another frontal passage is possible toward end of this
forecast valid period.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 121 PM EDT Sat Jun 22 2024

We`ll start the period with VFR conditions as high pressure keeps
the area dry. However, a cold front arrives around midnight
and this may provide showers and thunderstorms to the area. At
this point, feel more confident in SBN getting thunderstorms and
perhaps some MVFR VISBY reductions (in a tempo group). FWA
appears more likely to receive showers as the line looks to
become outflow dominant and lose its strength between SBN and
FWA. Either way, have more confidence in a deck of MVFR CIGs
starting just after 10z at SBN and around 12z at FWA. Moderation
back to VFR will be possible in mid to late morning as the
front continues to sink southward. Winds, initially
southwesterly with gusts up to 25 kts today, will veer more
westerly and northwesterly behind the front on Sunday with
gusts up to around 25 kts once again.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
     INZ005>008-012>015-020-022-023-103-104-116-203-204-216.
     Excessive Heat Warning until 8 PM EDT this evening for INZ009-
     017-018-024>027-032>034.
OH...Excessive Heat Warning until 8 PM EDT this evening for OHZ001-
     002-004-005-015-016-024-025.
MI...Heat Advisory until 8 PM EDT this evening for MIZ078>081-177-
     277.
MARINE...None.

&&

$$

DISCUSSION...Marsili
AVIATION...Roller