579
FXUS63 KIWX 132254
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
654 PM EDT Thu Jun 13 2024

.KEY MESSAGES...

- Scattered strong to severe storms are possible until midnight
  EDT, with the main threat being damaging wind gusts.

- A long duration heat wave begins on Sunday, June 16th. Highs
  will be in the low to mid 90s with heat indices upwards of 100
  to 105 degrees starting on Father`s Day through at least the
  middle of next week! Can`t rule out a few low chances (20% or
  less) for showers and storms but this timeframe looks mainly
  dry.

&&

.DISCUSSION...
Issued at 309 PM EDT Thu Jun 13 2024

Stay weather aware late this afternoon and evening as strong to
severe thunderstorms are possible. SPC has maintained a Slight Risk
(level 2 of 5) for much of our area. GOES satellite imagery this
afternoon shows ongoing clearing for much of the lower Great Lakes.
There is also a growing field of developing cumulus near Chicago out
ahead of the cold front that is currently over SE Wisconsin and NW
Illinois. High temperatures will approach the low 90s with dewpoints
in the low to mid 60s. Moderate MLCAPE of around 1000 J/kg combined
with ~40 kts of shear orthogonal to the aforementioned frontal
boundary will result in a favorable environment for severe
weather tonight. As the cold front and attendant shortwave
trough sweep eastward, storms should initiate between 4 to 6 PM
EDT over Lake Michigan and far southwest Lower Michigan. These
initial discrete cells could merge into clusters/a QLCS as they
grow upscale, although the latest hi-res model guidance still
differs in the coverage and intensity of this convection. Expect
storms to move south/southeastward throughout the evening
hours. Our southeast CWA may see additional storm development
after 8 PM EDT as an MCS develops in northern/central Illinois.
As storms initially develop late this afternoon, they may pose
an initial threat for hail, but as storms grow upscale, the
primary concern will become damaging winds. Inverted-v HRRR,
RAP, and NAM soundings have 800-1100 J/kg of DCAPE, indicating a
favorable environment for damaging downburst winds. Throughout
the event, damaging winds 60-70 mph will be the main threat
across much of the area, but hail 1-2" in diameter, torrential
rain, and a brief, isolated tornado or two are all possible as
well. In addition, PWAT values are around 1.5 to 1.75", which is
near the 90th percentile for this time of the year. This could
bode very efficient rainfall rates and some localized flooding
potential as well this evening (especially in the SW CWA where
additional storm development is possible). Most storms should
dissipate before midnight EDT, but a few may linger in the SW
CWA as late as 3 AM EDT Friday.

Friday and Saturday look to be slightly `cooler` (highs upper 70s to
mid 80s) and dry in the wake of the cold front. However, starting
Sunday, the first prolonged stretch of hot and humid summer days
will begin! An early season heatwave is likely, with high confidence
in near record temperatures and increasing humidity. Surface high
pressure and impressive upper level ridging will build across much
of the eastern CONUS this weekend, setting the stage for a `heat
dome` to set up. Highs will be in the low to mid 90s with heat
indices pushing 100 to 105 degrees starting on Father`s Day through
at least the middle of next week! Near record overnight lows in the
low to mid 70s will offer little to no relief from the heat. This is
the typical summertime "Ring of Fire" pattern for the Upper Midwest
and Great Lakes regions where any clusters of storms can develop and
tend to ride around the periphery of the heat dome. For the next 3
to 7 days, subsidence should keep precipitation chances at bay, with
only a few low chances (20% or less) for rain/storms).

There is growing confidence that Heat Advisories or even an
Excessive Heat Warning may be need for next week. Prepare now for
the incoming heat wave next week! Those without AC, elderly or young
children, or who are susceptible to heat may be especially
vulnerable. Find out where cooler shelters are in your town, stay
hydrated, and prepare to limit activities outdoor during peak
heating hours.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 648 PM EDT Thu Jun 13 2024

The existing TAFs were generally in good shape. Adjustments
were made based on current radar and anticipated trends. Showers
and storms are generally on a weakening trend as they exit KSBN
and approach KFWA. Therefore, I offer a dry TAF at KSBN and
have downplayed the previously advertised G45kt at KFWA.
Guidance continues to hint at a 30% probability of MVFR ceilings
near 09z tonight, but ceilings have trended higher since six
hours ago. Thus, that trend was adjusted in the TAFs.

It should be noted that showers and thunderstorms can pass south
of KSBN later tonight. This would stem from the TSRA currently
over extreme western IL. Therefore, this area will be monitored
closely. Non-zero chance this activity survives to KFWA, but it
seems unlikely.

&&

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

&&

$$

DISCUSSION...Johnson
AVIATION...Brown