108
FXUS63 KIWX 071003
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
603 AM EDT Tue May 7 2024

.KEY MESSAGES...

- Severe storms are likely this afternoon into the evening. The
  primary threat with any severe storms that occur include
  damaging winds, large hail, and even a few tornadoes. Heavy
  rain and minor flooding are also possible. Confidence is
  medium at this time.

- Isolated strong to severe storms are possible again Wednesday
  evening into the overnight hours, mainly south of a line from
  LaPorte, IN down to Lima, OH. Damaging winds, large hail,
  heavy rain, and localized flooding are the primary threats.
  Confidence is low at this time.

- Cooler with chances for showers and thunderstorms later this
  week into the weekend. Highs Friday into Sunday will be in the
  50s and 60s. Otherwise, expect temperatures in the mid to
  upper 60s and 70s.

&&

.DISCUSSION...
Issued at 536 AM EDT Tue May 7 2024

The day 1 SPC outlook was upgraded to expand the enhanced risk for
severe storms across much of our area, with a slight risk elsewhere.
Confidence has increased in at least scattered severe storms
developing in the 2 to 10 pm EDT time frame, and much of the model
guidance is within that general window. Confidence in the event
occurring as forecast overall is medium, with less confidence in the
exact intensity/exact location of the strongest storms. However,
feel SPC has a great first guess at the most likely location of the
worst storms-and greater tornado risk.


Models are in reasonably good agreement regarding the overall event
evolution and general parameters. As of this writing, a warm front
extends from southwestern IA and into far southern IL/IN. This warm
front will lift north through the afternoon as the LLJ takes aim at
our CWA this morning, orienting itself E-W just south of the IN/MI
border (depending on the model) by 18z. By 00z, the front will
extend across Lower Michigan, with the cold front along the western
Lake Michigan shore down through the IN/IL Stateline. This cold
front will cross our southern/central CWA from the evening into the
overnight hours.

Models suggest two main rounds of thunderstorm activity. The first
is a squall line, which is entering IL at the moment. This line will
likely decay some as it moves eastward, reaching our area this
morning sometime around 10 am. There could be a few showers that pop
up with the moisture/warm air advection out ahead of the line, so
have pops increasing after about 8 am EDT. It is possible that the
line holds together or reinvigorates a little bit later this
afternoon in the northern portions as the environment becomes more
unstable, but the threat of severe weather before 2 pm EDT is low.
This line also adds some uncertainty to the afternoon forecast, as
it will likely leave behind outflow that can limit destabilization
at first. However, given the lull in between the two rounds (could
be a few hours), I think we`ll be able to recover adequately. Cooked
outflow (from daytime heating) can sometimes be helpful fuel and
lift for storms later on (and vorticity augmentation in
mesocyclones/moisture pooling-both favorable for tornado
development).

The second round will develop behind the exiting morning/early
afternoon line, but models disagree on exactly where and how long it
takes before these discrete cells develop (again, what are the
leftover boundaries and environmental conditions after round 1).
Some are as early as 18z in IL/IN and others are later like the NAM,
which is closer to 21-00z for initiation in IL, moving eastward into
IN in the later evening/overnight. Either way, the environment will
likely be conducive to discrete supercells, with 50-70 knots of bulk
effective shear, 0-1 km bulk shear of 20-30 knots, and PWATS upwards
of 200 percent of normal. Surface based CAPE in the 18-00z time
frame is higher than what we usually see in this area---around 1500-
2500 J/kg! Some of the models suggest closer to 3000 J/kg. LCL`s are
around 500 to 1000, with the dewpoints in the warm sector (close the
enhanced risk area) in the low to even mid 60s. Mid level lapse
rates are another factor I`m not too impressed with---usually our
better severe weather events we have 7-8 C/km lapse rates in the 500-
700 mb layer but for this event models really suggest more like 5.5
to 6.5 C/Km (outlier is the NAM, which has LR of 7 to 7.5 C/KM).
However, given the other factors at play, we have plenty of severe
weather ingredients to work with-and I think it warrants paying
attention to. It`s not out of the question with the SRH values of
100-200 m2/s2 and the higher cape/bulk effective shear/high moisture
we see a few stronger tornadoes.

Obviously focused most of this discussion on today-tonight, but
there is a severe threat for Wednesday night as well. However, it is
looking less likely than yesterday, and delayed slightly (yesterday
threat included the afternoon hours). The better threat will be
south of our area, but we could see some stronger storms (SPC kept
us in a marginal risk generally from LaPorte, IN to Lima, OH and
south and west from there). Otherwise, rain is likely with
thunderstorms. Confidence in severe weather threat is lower, with
the main hazards (if any) being damaging wind, large hail, and heavy
rain with localized flooding.

Expect wet weather to continue through early next week, with chances
for showers most days. Thunderstorms are possible. It will be
slightly cooler, with highs will be in the 60s this weekend.
Temperatures warm back into the mid to upper 70s by early next
week.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 601 AM EDT Tue May 7 2024

Spotty MVFR cigs will likely linger in the vicinity of the
terminals this morning as moisture begins to stream northward
in advance of a warm front. This warm front will lift into
northern IN late this morning and afternoon with a couple rounds
of convection expected. The first will be associated with a
decaying line of convection that will track through from west to
east late this morning into the early afternoon. Moisture
advection in advance should allow cigs to range in the MVFR to
low VFR with an hour or two of showers and embedded thunder
expected. Greater concern is for a round of more vigorous
surface based convection mid-late afternoon as instability
increases just in time for a MCV to track through with scattered
strong-severe storms. VFR/dry otherwise into tonight behind
this feature.

&&

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

&&

$$

DISCUSSION...MCD
AVIATION...Steinwedel