499
FXUS63 KIWX 251012
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
612 AM EDT Tue Jun 25 2024

.KEY MESSAGES...

- There is a slight to marginal risk for severe weather today.
  One round will be this morning between 7 am and 12 pm EDT,
  then the second, be the 3 pm to midnight EDT. Damaging winds
  and heavy rain are the main threats, but hail and localized
  flooding are possible. Confidence is medium in severe weather
  occurring, greatest confidence with the first round of
  storms.

- High temperatures will be in the 80s, with some locations
  largely along and west of Interstate 69, especially south of
  US 30, will see high temperatures in the upper 80s with heat
  indices possibly reaching the mid to upper 90s. Confidence is
  low because of cloud cover and precipitation chances.

- Dry conditions return later Wednesday into early Friday
  afternoon, with highs in the 70s and 80s.

&&

.DISCUSSION...
Issued at 532 AM EDT Tue Jun 25 2024

Well this is certainly going to be a low to medium (at best)
confidence forecast, with model guidance all over the place in terms
of what`s ongoing now, and then how we expect things to evolve all
day in terms of storms.

The first (and potentially only) round of storms, currently over
WI/North-Central Lake MI as of this writing, will likely move in
from the north between 7 am-11 am EDT. Storm motion will be
southeast around 60 mph, with damaging winds and heavy rain the main
threat. Hail is also possible. Storms are currently strong to
severe, but are expected to weaken as they reach our area later this
morning...but by how much? I am always hesitant to poo-poo a severe
risk with an MCV around, as they tend to have their own environment
and can be full of surprises. Have categorical pops, particularly in
the northeast (in line with the 5z HRRR/5-7z RAP). The latest HRRR
and NAMNest models bring in likelihood of precipitation across the
entire northern CWA for the morning (vs confined to eastern
positioned RAP). This was a flip flop back to the earlier model
solutions by the HRRR...so not sure how well to trust that.

If the HRRR is correct...the line/MCV drops southeastward through
our CWA throughout the day, possibly intensifying later in the
afternoon as it gets south of US 24.

If the RAP solution (or something like it is correct), the morning
round will be less extensive, confined to NE IN/NW OH/SE Lower MI,
exiting (or diminishing) by the afternoon. It then generates a
second round of convection west over IL and that spreads eastward
along the slowly meandering cold front (3 pm-midnight EDT).
Confidence is much lower with regards to the second round of storms,
mainly because we don`t know how the incoming MCV will impact our
environment. What kind of boundaries will be around? Will the
subsidence behind the exiting morning wave limit any development
afterwards? Will round 1 completely dissipate and limit cloud cover,
making it warmer and possibly more unstable for the afternoon? More
questions than answers...

The bottom line is...pay attention today for watches and warnings.
SPC has our area in either a slight/marginal risk for today, and I
feel that`s reasonable. Just with the ambient synoptic environment
we have about 30 knots of bulk effective shear, perhaps as much as
1000-2000 J/kg of surface cape (upwards of that in MUCAPE), and mid
level lapse rates of 7-8 C/KM. Dewpoints look to be in the upper 60s
and low 70s (some models had low to mid 70s, which is not totally
insane given there are observations with those values in western IL
as of this writing. LCL values are on the lower end as well. I
wouldn`t be surprised if we had an isolated tornado given ll
moisture and the presence of an MCV, but I`d expect the predominant
hazards with any severe storms to be damaging winds and heavy
rainfall/localized flooding.

Given the chances for showers and storms, and the fact that models
are already seriously underdoing the cloud cover (thanks to the
overnight storms over IL that were not captured well by model
guidance), opted to lower high temperatures slightly to be
around the mid-upper 80s. With the humidity comes higher heat
indices...which look to be around 90 degrees for most. The best
chance of seeing values closer to 95-100 degrees (our advisory
criteria) would be south and west, as they have time to warm up
before the MCV and associated precipitation/cloud cover arrive
(Especially assuming the RAP is right, as the better cloud cover
is going to be east). Held off on advisory headline for now
given tremendous uncertainty, and mentioned in the HWO.

Last but not least in regards to the immediate short term, with the
MCV and ongoing convection on the lake, expect we`ll have a higher
swim risk than what it appears to be based on wave heights alone. In
addition to wave heights being higher near thunderstorms, water
level fluctuations are occurring from the mid lake storm pressure
perturbations. Calumet Harbor IL (southern Lake MI) dropped suddenly
by 1 ft, Port Inland MI (northern Lake MI) by a half of a foot. I
expect this to intensify as the bowing segment continues to dive
southeastward. Outside of that, winds will be south-southwest, with
waves climbing to around 2-3 feet. This is favorable for strong
longshore and structural currents (where piers are present). Rip
currents are also possible within the sandbars, especially if we see
those continued water level fluctuations into the morning and
afternoon hours. For today, have kept the moderate swim risk for
Berrien County, MI and have La Porte in a low swim risk. However,
depending on how things evolve with the incoming storms-an upgrade
to high swim risk for at least Berrien may be warranted (perhaps
upgrade to moderate for La Porte). Water level fluctuations from
seiches/meteotsunamis can cause sudden dangerous current development-
despite lower wave heights.

Beyond the short term, expect Wednesday to feature additional
chances for showers and storms associated with an incoming mid level
trough, however where the best potential is will depend on how far
the cold front from today`s storms makes it southeast before
stalling and (possibly) lifting back northward. It`s possible we see
a period of heavy rain Tuesday night into Wednesday as the LLJ pumps
moisture up over the front. Severe weather is not expected, but
could see some ponding on the roads or minor flooding if the front
stalls and storms redevelop along it.

Dry conditions return for mid-late week, with highs in the 70s and
80s. The next chances for rain will be Friday afternoon into
Saturday.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 606 AM EDT Tue Jun 25 2024

A line of thunderstorms is racing southeast along the eastern
shore of Lake Michigan. Wind gusts of 60 mph have been recorded.
A gradual weakening trend is anticipated but this has not been
observed quiet yet. Upstream observations will be monitored
closely and amendments will be made to KSBN as needed.

This complex has a greater likelihood of weakening by the time
it reaches KFWA, but this will need to be monitored closely as
well.

Additional storms are possible this evening, resulting in
PROB30s for now. Morning storms could either squash or enhance
the evening risk.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 2 PM EDT this afternoon for LMZ043-
     046.

&&

$$

DISCUSSION...
AVIATION...Brown