681
FXUS63 KIWX 140453
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1253 AM EDT Sun Jul 14 2024

.KEY MESSAGES...

- There are periodic chances for showers and storms (20 to 50%) tonight
  through Tuesday night, with one or more rounds of strong to
  severe storms possible during this timeframe.

- Hot and humid conditions possible Sunday and Monday, depending
  on storm coverage, timing, and cloud cover. Afternoon heat
  indices mid 90s to near 100 degrees.

- Cooler, drier weather is anticipated midweek through next
  weekend.

&&

.UPDATE...
Issued at 910 PM EDT Sat Jul 13 2024

A cluster of thunderstorms from north central Illinois has
gradually been on a diminishing trend as it entered northwest
Indiana early this evening. Some lingering outflow gusts to 20
to 30 mph will be possible across the far northwest over the
next hour as weak surfaced based CIN begins to develop. A more
mature MCS is ongoing across central/southeast Wisconsin, and
present indications would suggest favored path of this MCS to
ride instability gradient into SW Lower Michigan/northwest
Indiana after 04-05Z. MLCIN will continue to develop ahead of
this line this evening, but outflow should provide enough
forcing to overcome this low level CIN and maintain convection
into the local area. Background shear is marginal across the
area and may have difficulty in striking a balance with the cold
pool shear. Maintenance of this convection will likely occur
through regeneration of cells along the outflow boundary.
Widespread severe weather is not expected, but SPS level gusts
and a few gusts to 40 to 50 mph are a possibility in the
05Z-08Z timeframe across the far northwest. Will make an evening
update to increase PoPs across northwest half of the area for
the early overnight hours given increasing confidence in parts
of the area being affected.

&&

.DISCUSSION...
Issued at 227 PM EDT Sat Jul 13 2024

To be straightforward, this is a tricky forecast. There is quite a
lot of boom or bust potential in the coming days, as our CWA could
see multiple rounds of severe weather, just one round, or even
nothing at all. Our CWA is on the periphery of a building ridge in
the Plains, and with northwest steering flow, this puts the Upper
Midwest and Great Lakes regions in a very favorable zone for storms.
Several strong shortwaves that drop into the Midwest in the coming
days may help to sustain convection. There is potential one or more
rounds thunderstorm activity could be severe in our CWA, as SPC has
us in a Day 1 and Day 2 Marginal Risk (level 1 of 5) and a Day 3
Slight Risk (level 2 of 5).

The airmass moving in from upstream will be very unstable, with one
or more MCSs potentially developing tonight through Tuesday night
across the upper Midwest. Do these storms move east into Michigan or
dive south/southeast into Illinois and Indiana? Do one or more MCSs
overrun the most favorable environment and decay before making it
to our area? How many rounds of storms do we get? These are all
unanswered questions we still have...the first chance for storms
will come Sunday morning and afternoon. Some of the hi-res models
depict an MCV/remnant clusters of convection from a decaying MCS
moving southeast Sunday morning to early afternoon across the area.
With ample MLCAPE 2000-3000 J/kg and DCAPE 1200+ J/kg, damaging
winds would be the main hazard should these storms intensify. Given
low confidence in storm development and timing, have opted to keep
broadbrush 30-40% PoPs tonight into Sunday.

With all of the uncertainty with storm chances, this also means the
temperature forecast is low confidence through Tuesday. Heat and
humidity build Sunday and Monday, with highs in the low 90s and heat
indices potentially in the upper 90s to low 100s. Heat Advisory
headline could be needed. Uncertainty in storm coverage, timing, and
lingering cloud cover could all result in temperatures being lower
than what is currently forecasted.

At this point, my highest confidence in storms and chances for
severe weather is with the cold front Tuesday. An upper level trough
will pivot through the Great Lakes, resulting in chances for storms
ahead of and along the front. A continental, cooler airmass from
Canada will sink south midweek, resulting in seasonable highs in the
70s, a stark decrease in humidity, and dry conditions.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1234 AM EDT Sun Jul 14 2024

Northwest flow was setting up across the Upper Midwest into the
Upper Great Lakes regions with upper level disturbances embedded
in this flow. At the onset, a pair of systems were upstream with
associated convective complexes. The closer one was just upstream
over northeast IL across Lake Michigan. Updated TAFs to include
the latest expectations from this system with the timing of this
system with storms with wind gusts to around 30 knots at SBN.
Some lingering precipitation with embedded thunder is likely after
the initial line in the trailing stratiform area. Otherwise, great
uncertainty prevails with the evolution of outflow boundaries and
subsequent development of convection. For now, just went with
evening VCTS at both sites. Updates to this timing and coverage
will likely be needed.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...Air Quality Alert until midnight EDT tonight for MIZ177-277.
MARINE...None.

&&

$$

UPDATE...Marsili
DISCUSSION...Johnson
AVIATION...Skipper