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429
FXUS63 KIND 220150
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
950 PM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Hot weather persists today and Saturday
- Chance of showers and storms late Saturday night into Sunday
- Potentially very hot on Tuesday
- More thunderstorms possible Tuesday into Wednesday
- A brief respite from heat and humidity late next week

&&

.FORECAST UPDATE...
-- Changed Discussion --
Issued at 950 PM EDT Fri Jun 21 2024

Another warm night is in store for central Indiana as the broad
subtropical ridge remains in place over much of the continental US.
Several local airports were reporting 82F at 935P, while Bloomington
had dropped to 79F.  Light southwesterly winds will continue to
diminish this evening to near calm under mostly clear skies.
Temperatures will bottom out in mainly the low 70s, with readings
closer to 75F in the Vincennes area.  Dewpoint depressions of 5 or
more degrees will discourage fog formation...although patchy/brief
visibility reductions cannot be ruled out through pre-dawn hours.
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&&

.SHORT TERM (This evening through Saturday)...
Issued at 323 PM EDT Fri Jun 21 2024

Rest of Today and Tonight...

Diurnal cu has developed across central Indiana, with convective
temperatures now met as of early this afternoon (88-89). This 30-50%
cloud cover should continue through the late afternoon, with a slow
decline this evening within surface cooling before mostly clear
conditions become the rule overnight.

Surface temperatures have plateaued some as the PBL has become well
mixed. However, temperatures should begin to increase again over the
next few hours with surface fluxes increasing in an already well
mixed airmass. Current observations show temperatures in the upper
80s, with highs currently expected to be between 93-95 across the
region.

Overnight temperatures will once again efficiently cool as the PBL
becomes decoupled, pushing surface temperatures towards dew point
values. Still, 25-30 degree dew point depressions will help mitigate
the ability for surface temperatures to reach saturation in most
areas; outside of water ways and well irrigated fields. With this in
mind, the current expectations is for morning lows in the low 70s.

Tomorrow...

Similar conditions will exist tomorrow as central Indiana remains
within a heat dome underneath anomalously high heights. This should
keep temperatures in the low to mid 90s over much of central
Indiana. Modest mid-level lapse rates will also still be present,
providing the necessary parameters for diurnal cu development
once again tomorrow afternoon.

The main difference will be increasing low to mid level winds out
ahead of an approaching low level wave. This wave will be the main
culprit for convective development over the Great Lakes region
tomorrow, but will also provide an uptick in surface winds over
central Indiana. An increasing 900-800mb pressure gradient ahead of
the wave should also lead to modest gusts in the afternoon once the
PBL mixes up into the 15-20kt LLJ.

The aforementioned upstream convection will provide low rain chances
late on Saturday, but the bulk of this threat is likely not to reach
the Indiana border til will into Saturday night.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 323 PM EDT Fri Jun 21 2024

The long term forecast features a couple of opportunities for heat
relief, at least one or two additional stiflingly hot days, and a
couple of opportunities for potential convection, some of which may
be organized and present at least a low potential for strong to
severe storms.

The large scale ridge currently over the region will steadily
retrograde into the southern Plains and Desert Southwest over the
next few days into next week, providing some heat relief but also
placing us in a potential zone for one or more rounds of convection.

Conditions will remain quite warm and humid, but slightly less so as
the ridge moves.

The first potential for convection comes tomorrow night into Sunday
as a system cresting the ridge moves into the region, and frontal
forcing along with ample upstream destabilization will allow for
some organized convection to develop late in the day on Saturday,
progressing downstream Saturday night. Diurnal timing is somewhat
unfavorable and overall shear is relatively weak, but depending upon
the strength of the initial convection and subsequent upscale
growth/cold pool development, a localized damaging wind threat
cannot be ruled out as storms, which may be weakening, move into the
area late Saturday night. The storms, or associated boundaries, may
promote redevelopment/reintensification during the day on Sunday,
again with a localized damaging wind threat. Uncertainties are
plentiful, and current day 2/3 marginal risks from SPC are
reasonable.

The next opportunity looks to come primarily Tuesday evening into
Wednesday. While there will also be synoptic scale support for this
round, this looks to be a bit more analogous to the traditional
"ridge rider" scenario, with very strong instability/modest shear
contributing to the development of one or more QLCSs, which then
drive south/southeastward into the instability axis Tuesday evening
into Wednesday. Uncertainties increase with time, particularly given
that prior days` convection will significantly influence subsequent
days, along with typical guidance spread, but experimental CSU
machine learning guidance is highlighting late Tuesday into Tuesday
night as a time frame to watch for an organized severe threat.

Sunday night into early Tuesday and late Wednesday and beyond appear
to have good chances of remaining dry for now.

Temperatures will moderate somewhat with the movement of the ridge,
but humidity will remain high until late in the week, particularly
ahead of the boundaries that will move through the region as
moisture pools. This will promote continued, but mostly typical,
summertime heat, with the possible exception of Tuesday, when
depending upon convection timing and associated cloudiness, highs
could reach back into the low to mid 90s with dewpoints approaching
or exceeding 70, producing afternoon heat indices in the low 100s.
NBM`s hot bias, particularly when dealing with the aforementioned
potential failure modes, necessitates some adjustment to highs
Tuesday, but regardless, we anticipate sticky, uncomfortable
conditions that day, possibly followed by severe storms.

Some relief may come late in the work week, particularly in the form
of lower dewpoints, but unfortunately as we move toward the end of
the month, this may be relatively short lived.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 732 PM EDT Fri Jun 21 2024

Impacts:
 - Southwest winds after 15Z Saturday gusting to 15-20KT

Discussion:

VFR conditions will continue under the hot midsummer pattern with
Indiana aligned along the northern portions of the broad subtropical
upper ridge stretched over the US.  Surface low pressure over the
central High Plains this evening will eject to Lake Michigan by
Saturday evening...promoting a strengthening gradient over central
Indiana during the day Saturday with southwest flow after 15Z
Saturday sustained at 9-13KT, with gusts to 15-20KT in the afternoon.

Otherwise FEW/SCT clouds through the TAF period will oversee light
winds tonight which may promote brief/minor visibility reductions
from patchy fog...with confidence too low to include in any TAF.
Any convection/-RA from the passing wave should not reach
KLAF/KIND until after the end of the TAF period.

&&

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

$$

UPDATE...AGM
SHORT TERM...Updike
LONG TERM...Nield
AVIATION...AGM