251
FXUS63 KIND 231859
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
259 PM EDT Thu May 23 2024

.KEY MESSAGES...

- Scattered to numerous showers and storms south, but dry north this
  evening. A few strong storms possible.

- Showers and thunderstorms Friday afternoon and evening. Some
  storms may be severe with strong gusty winds.

- Showers and thunderstorms likely on Sunday. Severe thunderstorms
  are possible.

- Temperatures expected to return to near normal next week

&&

.SHORT TERM (This evening through Friday)...
Issued at 259 PM EDT Thu May 23 2024

Rest of Today/Tonight:

Once again central Indiana will have split conditions between
northern and southern locations as a boundary has set up along the I-
70 corridor. This is being further reinforced by ridging to the NE
with dew points falling into the low 40s across northern central
Indiana.

For now, conditions will remain fairly quiet with scattered upper
level cloud decks. This should allow for afternoon temperatures to
increase quickly with highs near 80 across much of the state. Winds
have gradually veered back towards E/SE as well with another low
level wave helping induce the greater southerly component. This
should veer winds even further to the south throughout tonight into
tomorrow.

The main weather hazard for today will be the redevelopment of
convection later this evening ahead of the aforementioned wave. The
best parameter spacing will remain south of central Indiana where
greater surface lapse rates and moisture reside, but there is enough
850-500mb shear/instability for organized updrafts and isolated
strong thunderstorm development. The current expectation is for any
hail to be capped at 1/2" in diameter and gusts up to 45MPH, however
severe criteria cannot be ruled out. A majority of the convective
development should remain between 8PM and 2AM across the area, but a
few lingering showers/weak storms are possible into the late
night and morning hours.

Friday:

Once again, central Indiana will be under a threat of thunderstorms,
although this time with a greater threat for severe criteria.

During the daytime hours, conditions should be rather mundane with
moisture increasing throughout the day due to another, more potent
wave, approaching from the west. Given the amount of moisture return
throughout the day, marginal isentropic lift may be enough for a few
isolated showers/weak storms between 10AM and 4PM, but otherwise dry
weather is expected. Mostly clear skies and southerly flow will help
push highs back into the low to mid 80s tomorrow as well.

The more significant weather will be associated with a developing
pressure trough (from a prior day MCS) late tomorrow into tomorrow
night. CAMs are currently widely spread on timing of CI tomorrow
across central IL, with a broad range in timing of between 4PM and
11PM. Central Indiana`s threat would then begin shortly following
CI, with convection pushing into western IN an hour or two later.

Any convection that does develop should quickly grow upscale with a
majority of the forcing provided being linear. High DCAPE and a
strong mid level jet will be the main culprit, for the increased
damaging wind gust threat over most of central Indiana. The biggest
mitigating factor for severe winds will be the tendency for the MCS
to become outflow dominant due to the lack of substantial upper
level shear, thus the greatest threat for damaging winds will be
over western portions of the area (Closer to CI). Regardless, at
minimum, a 40-50MPH wind threat looks likely even in an outflow
dominant MCS, primarily contained to greatest thunderstorm cores.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 259 PM EDT Thu May 23 2024

A fairly active pattern is ahead of us as split flow looks to
dominate through the weekend. Mean troughing over the western states
diverges over the Plains, leaving us with a brief period of ridging
on Saturday. That should lead to a rather pleasant day in an
otherwise stormy weekend.

Sunday...

On Sunday, a potentially significant shortwave emerges from the
Plains. Guidance is in good agreement on this trough inducing
cyclogenesis and then taking the resulting surface low to our
northwest. This does two things, one: it brings the system`s warm
front through Indiana early in the day and two: it then places us
well within the system`s open warm sector before a cold front sweeps
through. As such, we may see two rounds of weather on Sunday. The
first, associated with the warm front, may be a large area of rain
with embedded thunderstorms or a weakening MCS. The second round of
storms may be a bit more scattered in nature but potentially more
significant.

Taking a closer look at round one...it will primarily depend on how
the previous day`s convection evolves and when/where the warm front
is across Indiana. Model soundings show elevated instability, along
with a generally straight and long effective hodograph. A potent
synoptically-driven low-level jet looks to be developing through
Saturday night into early Sunday. This should promote strong theta-e
advection even during the overnight hours. Guidance currently shows
a sharp theta-e gradient across Indiana by 12z Sunday. This gradient
is roughly parallel with the long hodograph mentioned above.
Therefore, it is possible that this area (wherever it sets up)
becomes the corridor for downstream MCS propagation. Primary
hazards with this first round will be heavy rain, gusty winds, and
lightning. Uncertainties include: how organized does the previous
night`s convection get? Does an MCS develop or not? If so, where is
the warm front and theta-e gradient? Timing is also uncertain, as
there has been a bit of a northwestward trend within guidance over
the past 24 hours regarding the placement of the primary surface
low.

Now a closer look at round two...this round may be a bigger severe
threat for a few reasons. One, we will be deeper into the warm
sector with an even more potent low-level jet along with very
unstable air. Two, hodographs become very curved by Sunday afternoon
which supports supercells. And three, activity may remain discrete
due to some capping and shear vectors orthogonal to the system`s
cold front/pressure trough. Greater uncertainty exists with this
round, however, compared to round one. The reason being is that
position and timing of the surface low is still in question.
Additionally, the morning convection/rain could impact subsequent
development. Still, ensembles show an anomalously strong low
pressure system passing to our northwest with ample instability and
shear across Indiana. Environmental setups like these are
particularly concerning if everything can line up just right. As
guidance comes into greater agreement we will refine our
messaging...stay tuned for updates.

Monday and Beyond...

By Monday we`ll be in the wake of Sunday`s low with northwesterly
flow at the surface and aloft. A weak wave looks to dive down from
Canada late Monday into Tuesday. This may bring a chance of
showers/storms. Surface high pressure then builds in to finish out
the week. Ensembles show deep troughing aloft persisting for much of
the coming week. Therefore, there is an increasing chance of a
cooling trend beginning Monday. Temperatures may drop back to normal
or even slightly below normal values for multiple days.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 256 PM EDT Thu May 23 2024

Impacts:

- Scattered showers and isolated storms at southern sites today
  and this evening

Discussion:

Generally VFR conditions are expected. A few showers or
thunderstorms are possible at the southern sites this evening,
especially KBMG.

Will have to watch for some fog or stratus development overnight
tonight, but confidence is not high enough to include at this time.


&&

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

&&

$$

SHORT TERM...Updike
LONG TERM...Eckhoff
AVIATION...Updike