412
FXUS63 KIND 070645
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
245 AM EDT Tue May 7 2024

.KEY MESSAGES...

- Severe storms expected today, especially during the afternoon
  and evening. All forms of severe hazards are possible.

- Additional severe storms are possible Wednesday afternoon and
  evening. All forms of severe hazards are again possible.

- Heavy rain is possible at times through Wednesday night. Localized
  flooding will also be possible.

- More chances for thunderstorms mainly Thursday and Saturday.

- Normal to slightly below normal temperatures from Thursday
  into early next week.

&&

.SHORT TERM (Today and tonight)...
Issued at 245 AM EDT Tue May 7 2024

Tuesday Rd #1 | Strong but Mostly Sub-Severe | Between 9AM and 12PM

An ongoing MCS over MO will progress eastward overnight, propelled
by a strong LLJ. As this reaches the Ohio Valley this morning, the
LLJ will begin to wain, remaining stronger further west. Still,
sufficient 0-3km CAPE between 100-150 J/kg, and a sustained cold
pool should be enough to keep the MCS ongoing despite weaker LL
dynamics. The expectation is for this MCS to be over Indiana
between 9AM and 12PM.

Atmospheric disorganization and a lull in thermodynamic availability
will be the main mitigating factors for severe convection within
this initial round. An elongated low to the north will keep deep
layer shear elevated over the northern half of central Indiana, but
mid level lapse rates and theta-e advection ahead of the MCS will be
much weaker. The opposite will be true for the southern half of
central Indiana (Elevated Instability, but Weak Shear).

This should cause the storms over northern central Indiana to become
more shear dominant, with convection outrunning the UDCZ. For this
reason, the northern section of the line may briefly be near severe
criteria as it nears/enters Indiana, but should quickly weaken as it
progresses eastward.

The southern half of the storm then becomes the greater concern
depending on how quickly the cold pool moves eastward. Its possible
the cold pool becomes dominant on the southern half, and the main
concern then shifts towards initiation along the outflow boundary.
However, if balance does remain, there is high enough 0-3km CAPE,
and theta-e ingestion for potentially severe wind gusts along the
UDCZ for this first round.


Tuesday Rd #2 | Scattered Severe Storms | Between 3PM and 10PM

Even though this is round 2 of convection for the day, the storm
mode and overall hazards will likely not be the same over the entire
7 hour threat period. For that reason, I am going to split this
portion of the discussion into 2a (3P-7P) and 2b (6P-10P).


Round 2a (3P-7P): The remnants of the morning convective line will
be moving away by early afternoon with a capped lower level for
portions of the late morning and early afternoon. Any cap that does
form will quickly erode as rapid theta-e advection pushes a warm,
moist layer over central Indiana this afternoon. Broad diffluence of
the mid/upper level jet streaks along with this rapidly
destabilizing atmosphere should lead to scattered CI over central
Indiana around mid-afternoon.

Early on, multicellular clusters will be the more common storm mode
as overall parameter spacing remains moderated by sufficient, but
weak 800-700mb winds, and weak anvil level flow. Current
expectations for this initial time period are for 0-1 SRH to be
around 100, with CAPE beginning around 1500 J/kg. Effective shear
will still be plenty strong for updraft organization within
multicells, and an isolated wind and hail threat is likely. Poor
precip dispersion aloft within weak anvil level flow, may lead to
precip loading in the updraft, creating more sub-severe and melting
hail, but confidence is not high in this solution given robust
effective bulk shear.


Round 2b (6P-10P): The second half of this round looks to be the
most potent portion of the entire day. A pressure trough will begin
to develop across central Indiana late this afternoon into the
evening providing another source of lift and convective
organization. Shear vectors along this pressure trough remain
orthogonal keeping the storm mode mostly discrete. During this time
period, mid level lapse rates ramp up even further, pushing SBCAPE
values near 3000 J/kg. This along with better anvil level flow, and
a strengthening LLJ will likely lead to the formation of supercells.
This time period will be most concerning for areas along and east of
the I-69 corridor including the cities of Muncie, Indianapolis,
Bloomington, Shelbyville, Columbus, Rushville, Winchester, and
Seymour.

With the expectation of supercells during this time period, all
severe hazards are on the table. Strong 0-1km lapse rates, 0-1km
shear and low LCLs also intensify the tornado threat for this time
period, including the potential for a few strong tornadoes (EF2+).
Giant hail (2.5"+) will also be possible within strong updrafts of
supercells.

&&

.LONG TERM (Wednesday through Monday)...
Issued at 245 AM EDT Tue May 7 2024

Wednesday and Wednesday night...

A severe weather outbreak followed by heavy rain and flooding are
possible Wednesday afternoon and night as a surface low heads
northeast towards central Indiana in the fast southwest flow aloft
around the base of the High Plains upper low. This will allow a warm
front to lift northeast from southern Indiana to near the I-74
corridor by late afternoon. By Thursday morning, the associated
surface low will be somewhere near Muncie with a cold front sweeping
through from the west. Out ahead of the cold front and in the warm
sector to the south of the northeastward moving warm front, the
atmosphere will destabilize during the afternoon with CAPEs in
excess of 1000 J/kg. The combination of the instability, strong mid
level shear in excess of 50 knots and the synoptic forcing will
likely lead to rapid thunderstorm development during the afternoon
with all modes of severe storms possible. Model soundings are
afternoon curved hodographs with 0-3 km SRH near 200 and 0-1 km SRH
slightly over 100.

The biggest caveat to severe weather potential across central
Indiana will be how far northeast the warm front gets during the
afternoon and if discrete cells can form ahead of a likely MCS
approaching from the southwest. If the front doesn`t it make it as
far northeast, and the 00z runs are hinting at this scenario, severe
weather will likely be limited to our southwestern counties. This
has prompted a further southwest shift in the SPC Day2 severe
outlook, which has the Enhanced Risk south of Terre Haute and
Greensburg and the Slight Risk only as far north as Cicero and
Anderson. FWIW, CAMs favor the bulk of the MCS to move south of I-74
with little to no discrete cells ahead of it. Still, with
uncertainty, will continue with 80+ percent PoPs over all central
Indiana Wednesday night with 50 percent PoPs Wed afternoon
over southwestern counties tapering to 20 percent northeast.

By nightfall, the focus will shift more towards heavy rain and
flooding as PWATS increase to 1.5 inches or higher which is the max
moving average for this time of year. In addition, coupled jet
structure from jet maxes over the Great Lakes and southern states,
could enhance rainfall totals. DESI suggests an inch or more 24 hour
QPF is possible over south central Indiana and this looks to be on
the low side. Will make mention of heavy rain and flooding potential
in the HWO and in web site and social media graphics.

Thursday night through Tuesday...

A pair of upper waves in northwest flow aloft will bring decent
chances for convection to the area Thursday and again Saturday.
Otherwise, signal lacking for anything other than low chances for
convection for the rest of the weekend due to general troughy flow
aloft. Meanwhile, models are hinting at an approaching upper ridge
early next week which would tend to bring dry weather.

Temperatures look to be more on the cool side than recently with
normal or slightly below normal afternoon highs in the 60s and 70s.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1147 PM EDT Mon May 6 2024

Impacts:

- Line of convection will reach the terminals after 11z-13z
  with MVFR ceilings and visibilities and briefly worse
  flying conditions possible

- Good confidence more PM thunderstorms will develop and
  move across

- SE winds less than 10 knots will pick up and switch to the
  S and SW after 11z-13z. Gusts to 20 plus knots by this
  afternoon and possibly briefly with the morning gust front.

- Gusts to 50+ knots and large hail possible in severe storms this
  afternoon and evening

- Brief MVFR and worse fog can not be ruled out overnight and
  until the line of thunderstorms gets close


Discussion:

A line of dying thunderstorms will move quickly ENE across central
Indiana this morning. MVFR and possibly briefly IFR conditions are
possible along with gusty winds.

The atmosphere will reload this afternoon and and upper trough and
approaching cold front along with increasing instability and
moisture will result in rapid thunderstorm re-development this
afternoon. Strong and severe thunderstorms are possible with this
activity this afternoon.

Winds will become gusty and switch to the S and SW during the day
with gusts to 20+ knots away from convection up to 50+ knots in
severe storms.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Updike
LONG TERM...MK
AVIATION...MK