873
FXUS63 KIND 282122
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
522 PM EDT Tue May 28 2024

.KEY MESSAGES...

- Scattered showers and at least a few storms are possible late in
  the day and early tonight. Strong wind gusts are the primary
  hazard.

- Dry and Seasonable Wednesday through Friday, Rain chances Saturday
  into Sunday

&&

.MESOSCALE UPDATE...
Issued at 522 PM EDT Tue May 28 2024

Scattered convection continues to pulse up and down in intensity
across the northwest parts of the forecast area late this afternoon.
Storms have sporadically produced CG lightning strikes along with
pea size hail...the most recent confirmed near Lafayette just prior
to 21Z.

The current KIND ACARS sounding continues to show a narrow layer of
CAPE with MLCAPE values generally at 500 j/kg or less. Steep lapse
rates up through about 700mb are present with a noticeable dry layer
in the mid levels. With the freezing level hovering around
9kft...stronger cells will continue to carry a threat for small hail
into the evening. The greater threat from any stronger storms will
be gusty winds as the combination of the subsidence aloft with the
dry adiabatic thermodynamics through the boundary layer should
support easy transport of briefly stronger winds to the surface with
elevated cores.

Convective coverage will increase slightly after 23Z in response to
the upper wave over northern Illinois pivoting E/SE through the
evening. Greatest threat for rain and storms will remain near and
north of I-74...shifting east of the forecast area by late evening.

Additional mesoscale AFD updates may be issued through the evening.

&&

.SHORT TERM (This evening through Wednesday)...
Issued at 252 PM EDT Tue May 28 2024

Generally northwesterly flow exists through the depth of the
atmosphere today as a trough axis resides to our east. A short wave
embedded within the broader flow is currently diving to the
southeast out of central Canada. This feature should pass just to
our north this evening and overnight. Given the cooler air aloft,
associated with the trough, lapse rates are fairly steep today. RAP
soundings show 7-8 C/Km with super adiabatic values (up near 10C/km)
very near the ground. ACARS soundings out of IND do not show this
super-adiabatic near-surface lapse rates, however. Despite the steep
lapse rates, instability is modest with values generally between 500-
1000 J/Kg. This is in part due to a lack of moisture within the
boundary layer.

Enough lift is present within and ahead of the vort max that showers
and thundershowers are shown by most guidance. Observations tend to
agree with this, as weak radar echoes are beginning to develop in
northern Illinois and even into northern Indiana. Continued growth
is expected through the afternoon with greater concentration nearer
to the vort max. Given the steep lapse rates and relatively dry
column, strong downbursts/wind gusts are the primary hazard with any
shower or storm. Activity should diminish after 00z as diurnal
heating wanes and the boundary layer stabilizes.

Overnight, expect quiet weather with diminishing winds. Low-clouds
cover may develop towards morning from the north as the vort max
swings by. Wouldn`t rule out a few light rain showers within the
area of low clouds either. These low clouds may persist into the
morning hours but should dissipate as daytime mixing resumes and the
vort max pulls away. Surface winds should pick up again as well once
the boundary layer begins to mix. Gusts upwards of 20kt are possible
at times tomorrow afternoon. Temperatures look to be a bit below the
climatological average for this time of year due to the broad
troughing aloft. Typical values at IND are 77/57.

&&

.LONG TERM (Wednesday night through Tuesday)...
Issued at 252 PM EDT Tue May 28 2024

The long term will begin with our first consistent reprieve from wet
conditions as high pressure moves in from the north.

Troughing over the Mid-Atlantic region has brought a succession of
waves through the region, but as of Wednesday, confluence in the
upper jet stream and broad AVA will aid in raising heights through
the mid to upper atmosphere. Eventually, the amplifying ridge axis
will lead to surface high pressure over the Ohio Valley. Initially,
some semblance  of surface moisture will stick around on Wednesday
(DP in the low 50s). However, by Thursday, adiabatically warmed
subsidence should drop surface dew points in the mid to low 40s.

The combination of subsidence, and drying air will lead to quiet
conditions Wednesday night through Friday. Highs will begin to
slightly increase on Thursday and Friday (Mid to upper 70s) within
well mixed PBLs. Even with deep PBLs, the lack of a LLJ should keep
winds rather calm; expect winds to top out around 10-12kts Thursday
and Friday afternoons.

The next wave of moisture/lift looks to arrive late Friday through
Saturday. Although the upper wave may arrive Friday night, the dry
low to mid levels from prior day subsidence should keep any
precipitation from reaching the ground until sometime on Saturday.
Overall this system looks to be mostly showery due to poor mid level
lapse rates, but its still too far out to have high confidence in
the details. The forecast beyond Saturday becomes much more murky
due to the relatively elevated surface moisture and remnant
boundaries and weak surface level waves in the remnants of the
Saturday upper level system.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1238 PM EDT Tue May 28 2024

Impacts:

- Low probability showers and thundershowers between 22Z and 04Z.
- Gusty winds and temporary MVFR conditions possible in
  showers/storms.
- WNW wind gusts to 20-25kt possible today and tomorrow.
- Period of MVFR ceilings possible early Wed morning.

Discussion:

VFR conditions should persist through this afternoon. A weak storm
system diving down from the northwest may induce a few showers or
thundershowers towards the evening. These look to arrive somewhere
between 22Z and 04Z. Showers/storms will be fast-moving and will not
persist in any one location for a prolonged period of time. Brief
MVFR conditions along with gusty winds are possible with these.

Ambient surface winds will be out of the west-northwest between 10-
15kt with gusts 20-25kt. Winds decrease a bit overnight as the
boundary layer stabilizes but should pick up again Wednesday
afternoon.

A brief period of MVFR ceilings are possible Wed morning as the
center of the weak storm system swings by. These clouds should
diminish as the day progresses, due to boundary layer mixing and the
system itself departing eastward.

&&

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

&&

$$

MESOSCALE...Ryan
SHORT TERM...Eckhoff
LONG TERM...Updike
AVIATION...Eckhoff