271
FXUS63 KIND 021857
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
257 PM EDT Thu May 2 2024

.KEY MESSAGES...

- Warm and more humid today with chances for showers and
  thunderstorms tonight.

- Multiple chances for showers and storms throughout much of the
  forecast period, with continued above normal temperatures.

- Potential for severe weather during the middle of next week,
  highest chances Tuesday evening and Wednesday night.

&&

.MESOSCALE UPDATE...
Issued at 144 PM EDT Thu May 2 2024

Latest surface observations show a warm front lifting northward
across Indiana. Here in Indianapolis, surface dew points rose from
49 to 65 quickly after frontal passage. Concurrently, temperatures
have risen into the lower 80s. Satellite imagery shows a cumulus
field developing from the front southward, with the greatest
concentration of cumulus developing over the more forested/elevated
parts of central Indiana. ACARS soundings out of IND corroborate
this, showing a substantial amount of low-level moistening and
erosion of a weak capping inversion.

However, this weak capping inversion remains as of 17z...located
around 850mb. It can be seen in the characterization of the cumulus
field, which is relatively flat at the moment. As the boundary layer
warms, it is expected that this cap gradually dissipates over the
next several hours. It`s at this point that we`ll begin to see the
threat for isolated showers and storms, since lapse rates are quite
a bit steeper above just above the cap.

Model hodographs show a lack of shear through the depth of the
column (some faster flow exists above the CAPE profile but storms
may not reach high enough to feel the effects). With modest dry air
in the soundings above 850mb it is possible that a few of the more
robust updrafts produce gusty winds upon their collapse.
Additionally, an isolated instance of hail is possible, but may be
limited in size due to poor storm top venting and modest updraft
strength.

There are a few factors that should act to limit convection this
afternoon. These include a lack of large-scale lift and advection of
slightly drier air around the backside of a surface high to our
east. As this process occurs, higher-res models tend to concentrate
available buoyancy along and just south of the warm front. As such,
any showers and storms would likely be nearer to this boundary
compared to places further south. Overall, convective coverage will
likely remain isolated and spread northward with time.

&&

.SHORT TERM (This evening through Friday)...
Issued at 249 PM EDT Thu May 2 2024

As of 2pm, temperatures have climbed into the mid 80s across much of
central Indiana. With partly cloudy skies and a couple more hours of
heating...it is not out of the question that a few record high temps
are set before the day is out. A rather large cumulus field
signifies that we have reached our convective temps across most of
the area, however. This could act to limit further warming to only a
degree or two. Though some drier air filtering in from the south may
allow for a better rate of warming, especially south of Indy.

The aforementioned cumulus field has shown some vertical growth as a
low-level capping inversion is slowly eroded. Higher-res guidance
continues to depict a few showers or thunderstorms developing this
afternoon, especially near the warm front where richer moisture can
be found. Coverage will be limited, as large-scale lift is weak and
drier air is flowing from the south as mentioned before.
Nevertheless, ACARS/model soundings show sufficient mid-level dry
air for DCAPE values over 1000 J/Kg, which supports the potential
for gusty winds/downbursts. Additionally, lapse rates and CAPE
profiles support a marginal hail threat. Hail size may be limited by
weak storm top flow and a CAPE profile that tapers towards the top
of the hail growth zone. Overall, any strong wind gusts / hail will
be limited to the strongest updrafts...which will be very isolated
in nature.

Overnight, a cold front to our west begins to work its way into
Indiana. Richer moisture and forcing accompany it, and so our
chances for rain go up quite a bit. Most locations will see showers
at some point through tomorrow morning. A few thunderstorms may be
embedded within the area of showers, but weak lapse rates and low
shear should limit severe potential.

Rain slowly diminishes during the day on Friday as the front slowly
works its way through Indiana. Showers may persist on and off, along
with low cloud coverage, through the afternoon. Once the front
passes, gradual improvement is expected as we head into the weekend.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 249 PM EDT Thu May 2 2024

Friday Night Through Sunday.

Active weather is expected for much of the long term period with
near daily chances for showers and thunderstorms with the potential
for severe weather at times next week. The first round is expected
Friday night into early Saturday with the passage of a cold front.
There will be little instability and only 15-20kts of effective bulk
shear with this frontal passage, so not expecting anything more than
a few rumbles of thunder and up to a half inch of QPF. Model
soundings show much drier air working in the aftermath of the
frontal passage which should help skies to quickly clear out for
much of Saturday.

This break in the rain will be brief with the next cold front
passage expected late Saturday night into early Sunday. There will
be a weak wave associated with the southern jet which may enhance
precipitation across the southern counties along with the potential
for a decaying MCS out of the northwest associated with the main
system. The front should be through by the early afternoon with
drier weather returning into late Sunday.

Monday Through Thursday.

On Monday a rapidly deepening upper level low pressure system will
eject eastwards from the Rockies and begin to travel to the
northeast with broad ascent across the Ohio Valley as a LLJ begins
to advect warm and moist air through the column. This low pressure
system is expected to slowly move through the Dakotas through
Thursday with daily chances for showers and thunderstorms across
central Indiana along with the potential for severe weather.

The timeframe for highest confidence in thunderstorms are Tuesday
evening and again Wednesday night as the cold front associated with
the main system finally pushes through. During both of those
timeframes, damaging winds and large hail are possible with the
highest confidence in severe weather during the overnight hours
Wednesday night into Thursday which is when shear will be maximized
ahead of the frontal passage. The pattern will then shift late
Thursday into the weekend with cooler and drier weather as the flow
aloft becomes more northwesterly.

MMEFS river runs show that the expected rainfall of 1-3 inches
between now and next Thursday shouldn`t cause much more than a
prolonging of action stage to low minor flooding through next week.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 144 PM EDT Thu May 2 2024

Impacts:

- Convection possible this afternoon and evening.

- MVFR/IFR conditions possible in any convection that strikes a TAF
  site.

- Confidence for afternoon showers/storms is low.

- Confidence for overnight showers is high.

Discussion:

A warm front lifting northward across Indiana will allow winds to
become southerly, occasionally gusting to 20kt this afternoon.

Enough moisture and instability exists for a stray shower or
thunderstorm during the afternoon as the front lifts northward.
Coverage will be very widespread, and confidence that a shower/storm
impacts a terminal is low. Will carry VCSH/VCTS during the most
likely timeframe for this...should it occur. Any shower or storm may
briefly reduce affected terminals into MVFR/IFR conditions.

A more widespread area of showers and possibly a thunderstorm
arrives late tonight. Confidence with this is much higher, and all
terminals are expected to see rainfall and at least MVFR conditions.
Low-level moisture and cloud cover could allow MVFR conditions to
persist through much of the day on Friday.

A cold front then arrives late Friday afternoon, switching winds to
northwesterly and improving ceilings somewhat.


&&

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

$$

MESOSCALE...Eckhoff
SHORT TERM...Eckhoff
LONG TERM...White
AVIATION...Eckhoff