340
FXUS63 KIWX 210510
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
110 AM EDT Tue May 21 2024

.KEY MESSAGES...

- A strong to locally severe thunderstorm is possible between 6
  and 10 pm in NW Indiana/SW Lower MI as well as locally heavy
  rain.

- Strong to severe thunderstorms are possible late Tuesday
  night, mainly west of IN-15 and then again along and east of
  I-69 Wednesday afternoon and evening.

- Warm and muggy conditions to be replaced by somewhat cooler
  and less humid air late this week into the Memorial Day
  weekend with some chances for showers and storms.

&&

.UPDATE...
Issued at 732 PM EDT Mon May 20 2024

Freshening grids up to reflect current trends in the line of
showers and storms extending from Marcellus to Lakeville and
San Pierre. Outflow boundary was now ahead of the line, by
several miles further north, which should result in a slow
decrease in intensity over the next couple of hours. Damage has
been reported in parts of LaPorte county as the strongest storm
collapsed and the winds from the storm raced east. Some
additional convection is noted across NE IL in an area of weak
convergence. Even if this progresses east, it will be
encountering a stabilized airmass in the wake of the main line
which should help either dissipate them or at least keep them in
check. No other changes made to grids for now.

&&

.DISCUSSION...
Issued at 214 PM EDT Mon May 20 2024

Very summer-like pattern comes with summer like challenges for
convection over the next couple of days in a rather moist and
diurnally unstable environment. Highs the next several days will
soar well into the 80s

Initial focus, with greatest (albeit still somewhat reserved)
confidence being with impacts of a MCV set to move across SE
Wisconsin later this afternoon. While the best dynamics remain
northwest of the area, a spoke of the wave does clip far NW areas,
resulting in some weak convergence that may be sufficient to
develop scattered showers and storms in the 22-00Z time frame.
NAM suite overly unimpressed with the development with other
CAMs a bit more confident on some development (HRRR the
greatest). Much like yesterday, shear profiles are rather paltry
(20 kts or less) resulting in more pulse type convection that
could drop a good deal of rain in a short time along with some
threat for locally gusty winds/small hail. Confidence in
eastward extent in the 00Z-04Z period decreases with loss of
diurnal heating and continued NE track of the MCV removing the
already limited convergence. Concerned that likely pops this
evening may be overdone, but if it is going to occur, location
is about right. Have made some adjustments to pops to reflect a
bit more inland extent to the storms but continue with a
weakening trend into the overnight hours.

Between 9Z Tue and quite possibly through 4-6Z Wed the best
forcing will likely remain well north into MI with the warm
front and well west with the cold front, resulting in a dry
forecast despite increasing instability and shear during the
afternoon and evening hours. 700 mb temps of +11 to +12 C edge
in as well, further capping off any development. While a stray
shower or storm could form across northern parts of the area
during the morning and maybe late afternoon in the far W, by far
the best chances look to wait to closer to 6Z Wed and beyond as
a line of strong to severe storms will likely have moved across
IL and be edging into western areas. A few CAMs show some
possible additional development ahead of the line on more of a
pre-frontal trough late evening with the main line then catching
up. Several models show a fair amount of SFC based CIN taking
shape overnight and the 50 kts of 0-6 km shear actually
decreases just ahead of the approaching convection (still
maintained along and behind). If the line holds together into
the overnight hours, pockets of damaging winds and some large
hail would be the main concerns. Slight risk in NW areas appears
reasonable still for Tuesday night with greatest chances
remaining well west of the area across E IA/W IL where a
moderate risk for severe storms now exists.

Cold front will ease its way through Wednesday with the potential
for some lingering cloud cover early. CAMs vary greatly on potential
for development along and ahead of the front with stronger signals
maybe residing just SE of our area during the afternoon/eve hours as
better upper level dynamics take time to catch up with the front.
DY3 slight risk is warranted at this point, but may change over the
next 24 to 36 hours as the mesoscale impacts of Tuesday night`s
convection becomes more apparent. New blend of models expands the
likely pops well NW to match where the better chance for storms
may exist (SE third or so-roughly I-69 east) and lingers into
Wednesday evening. This could very well be overdone, but given
the proximity of the front can`t entirely dismiss.

Frontal boundary will settle south of the area, with models
continuing to indicate a weak disturbance edging north from TX
Thursday evening towards the Ohio Valley for Friday. Additional
waves move in from the northern Plains the rest of the weekend into
early next week resulting in several period of slgt chc to chc pops
over the holiday weekend. Don`t think by any means it will be a
washout, but something to monitor in the coming days. The cloud
cover will help keep it somewhat cooler during the day (70s).

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 108 AM EDT Tue May 21 2024

Showers and storms have weakened, and dry conditions will now
prevail through the day Tuesday. VFR ceilings will persist
through much of the day Tuesday, and southerly winds will pick
up in the afternoon with gusts up to 20-25 kts possible. Showers
and storms will be likely Tuesday night (likely arriving in
Indiana between 02-06Z), so chances for storms will need to be
added in subsequent TAF forecasts as confidence increases.
Storms may be strong to severe overnight Tuesday into early
Wednesday, and the primary concern is strong, gusty winds.

&&

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

&&

$$

UPDATE...Fisher
DISCUSSION...Fisher
AVIATION...Johnson