389
FXUS63 KIND 210538
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
138 AM EDT Tue May 21 2024

.KEY MESSAGES...

- A few showers and thunderstorms possible in the northwest this
  evening.

- Unseasonably warm through Tuesday...highs in the upper 80s, with
  overnight lows as high as 70 Tuesday night.

- Strong storms with a conditional severe risk Tuesday night through
  Wednesday evening.

- Heavy rain possible Wednesday afternoon and night

- Additional chances for rain and storms through the weekend

&&

.FORECAST UPDATE...
Issued at 937 PM EDT Mon May 20 2024

The forecast remains in good shape with only minor adjustments
needed. Expect quiet weather conditions overnight with subtle
surface and upper level ridging in place. An upper level wave moving
across northern IN earlier helped to initiate scattered
thunderstorms. The chance for storms further south and east
across central Indiana has decreased since forcing is very weak.
In addition, mean steering flow out of the west- southwest should
help to keep any developed storms from tracking into the area.

Rain chances were lowered for tonight due to the reasons discussed
above. There is still a slight chance for precipitation across far
NW counties where a shower or storm moving in from the west cannot
be completely ruled out. Look for decreasing clouds through
tonight with temperatures falling into the mid 60s.

&&

.SHORT TERM (This Evening through Tuesday)...
Issued at 258 PM EDT Mon May 20 2024

Clouds this afternoon have helped to slow down daytime heating as
temperatures have been fairly steady over the past few hours. This
should prevent parts of the forecast area from seeing 90 degrees
today but it is still relatively hot and humid for this time of
year.

An upper wave will move across the Great Lakes late today, weakening
as it arrives, which could bring some showers and thunderstorms to
the NW counties. A few cells could be strong but better shear and
instability will be further NW. Dew points will remain high and in
the 60s overnight so overnight lows will not drop much. Thus
expecting lows in the mid to upper 60s.

Tomorrow is expected to be another unseasonably hot day with highs
in the upper 80s expected and can`t rule out a few spots getting to
90. With this being the first multi-day heat event for the year,
tolerance for these temperatures is low so take precautions to limit
time outside during the hear of the day and drink plenty of water.

The next impactful system will be approaching the area through the
day tomorrow, leaving central Indiana in the warm sector before it`s
arrival. While dew points will remain in the 60s tomorrow, model
soundings show that the mid to upper atmosphere will be relatively
dry so sky coverage will likely be lower than today, allowing those
temperatures to warm. Did go with guidance on PoPs tomorrow which
lowered any precip chances to less than 15% through the day as rain
looks to remain north of the forecast area.

&&

.LONG TERM (Tuesday Night through Monday)...
Issued at 258 PM EDT Mon May 20 2024

After the very warm temperatures of the last few days...the pattern
will begin to transition as early as Tuesday night with the track of
a sharp negatively tilted upper trough into the upper Midwest poised
to flatten the ridging across the region. In its wake a messy quasi-
zonal upper flow regime will become prominent. With a remnant
frontal boundary lingering across the Ohio Valley into the
weekend...an active pattern sets up with multiple chances for rain
and convection likely to last through the upcoming holiday weekend.

Tuesday Night through Wednesday Night

This timeframe remains the focus for potential severe weather
although model guidance hinting more and more at this being more of
a conditional risk for more intense convection.

The primary area of concern for more significant severe weather
Tuesday afternoon and evening will be to our northwest across the
western Great Lakes back southwest into the Missouri Valley. Linear
convection will progress east and approach the northern Wabash
Valley near or just after 06Z Wednesday. Expect though that the
storms will arrive in somewhat of a weakening state as they move
away from the deep forcing aloft which will track to the north of
the region. Model soundings show instability decreasing and becoming
elevated overnight with moisture return through the boundary layer
not nearly as pronounced as further northwest. That being said...the
available BL shear present and the passage of a stronger 850mb jet
could enable convection to remains stronger with a damaging wind
threat well into the forecast area before diminishing...especially
if the line can lay down a mature cold pool. Still some questions to
sort out but there remains a low end threat for severe convection in
the 06-12Z timeframe Wednesday.

The 850mb jet will lift out to the northeast Wednesday morning while
overall shear profiles weaken during the course of the day. Appears
more and more that redeveloping convection and subsequently the
severe risk for Wednesday afternoon and evening will become
increasingly reliant on the remnant frontal boundary sliding into
the region along with available instability and moisture. And
ultimately all of those parameters will be dependent on low level
convective debris leftover from Tuesday night...and model soundings
and RH progs both hint that lower clouds may be a challenge to mix
out through the day Wednesday. Should enough heating take
place...the instability profiles in tandem with the frontal forcing
would be sufficient for another round of strong to severe convection
with a focus across the southeast half of the forecast area.

Damaging winds and large hail would be primary threats for Wednesday
afternoon and evening...with a sneaky concern for heavy rain as
little BL shear over the forecast area in tandem with a frontal
boundary nearly parallel to the mean flow aloft from the southwest
supports slow moving and possibly training convection. Add to that
precip water values approaching 1.50 inches and the deep moisture
component will be present as well. Setup appears most conducive for
flooding risks across south central Indiana into Wednesday night but
the position of the frontal boundary will become a critical
component in determining where the axis of heaviest rain would fall.
With the front likely to be somewhere across southern Indiana by
daybreak Thursday...convection will linger throughout the night.

Thursday through Monday

A quasi-zonal flow aloft sets up for late week into the weekend with
a pronounced subtropical jet as a factor. With the aforementioned
frontal boundary becoming nearly stationary over the Ohio
Valley...stage is set for a multi day threat for scattered
convection and locally heavy rainfall that is likely to last through
most if not all of the holiday weekend. Not expecting every day to
be a washout...but there will be daily convective risks across the
forecast area.

Waves aloft riding along in the progressive upper level flow will be
the primary catalysts in generating convection throughout the
extended but timing them out at this early stage is a challenge and
not necessarily a model strength. The addition of the front
remaining in the vicinity of the forecast area offers an additional
component to a messy...multicellular convective risk at times
through next Monday. The severe risk from Thursday through the
weekend looks low overall and will likely be more of the pulse
intensity variety where collapsing cells can toss out locally strong
winds within a moist and unstable environment. With detail limited
at this early stage...will carry a broad chance pops for scattered
convection throughout the entire period. Temperatures will be
dependent on timing of convection and cloud coverage...but
anticipate mid 70s to low 80s from Thursday through the weekend.

Beyond the holiday weekend...extended guidance remains consistent in
developing a western upper level ridge with a trough developing east
of the Mississippi River. This will trend temps cooler while
maintaining plenty of clouds and at least small threats for rain
throughout much of next week.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 137 AM EDT Tue May 21 2024

Impacts:

- VFR conditions to continue into late Tuesday night
- Southerly wind gusts around 18-26KT Tuesday afternoon...stronger
  gusts mainly near HUF/LAF

Discussion:

VFR conditions will prevail through the period as central Indiana
rests in the steadily tightening gradient between broad high
pressure along the Atlantic seaboard and a deepening surface low
advancing from Kansas to southwestern Ontario.  Can`t rule out a
shower near KLAF tonight...or VCSH over any terminal Tuesday as a
subtle warm frontal zone crosses the region, although confidence too
low to include in any TAF.  More organized convection should
approach KLAF/KHUF by the end of the TAF period.

The bigger story will be increasing south-southwesterly flow during
the day Tuesday, with afternoon/evening winds sustained at 8-15KT,
with highest gusts to 18-26KT through the evening at KLAF/KHUF, as a
strong low-level jet approaches the Wabash Valley.

&&

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

$$

UPDATE...Melo
SHORT TERM...KF
LONG TERM...Ryan
AVIATION...AGM