436
FXUS63 KIWX 132346
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
746 PM EDT Sat Jul 13 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.

&&

.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 /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 745 PM EDT Sat Jul 13 2024

A challenging aviation forecast this period with mid/upper
level northwest flow pattern and instability gradient sprawled
across the Great Lakes/Ohio Valley placing northern Indiana in a
potentially favored corridor for thunderstorm activity. Several
weak northwest flow waves noted this afternoon, with a small
cluster of showers and storms across NE Illinois. These storms
quickly became outflow dominant but have initiated sporadic
stronger cells along outflow boundary. This tendency should
diminish over next few hours as peak diurnal instability waves,
but a few isolated showers and storms may work into northwest
Indiana between 01Z-03Z. A more organized convective cluster
across central Wisconsin could pose some risk to affect KSBN
after 06Z tonight. Some question as to the sustainability of
this convective line, but orientation of instability gradient
could support this cluster reaching KSBN vicinity with some
thunderstorm outflow gusts. Another convective complex could
form later tonight across northern Minnesota and track southeast
into Sunday across northern Indiana. With a good deal of
uncertainty in timing and convective coverage, will defer
thunder mention for later forecasts. Light south winds tonight
to become south-southwest for Sunday with gusts to 15 to 20
knots during the day.

&&

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

&&

$$

DISCUSSION...Johnson
AVIATION...Marsili