518
FXUS63 KIND 121901
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
301 PM EDT Wed Jun 12 2024

.KEY MESSAGES...

- Quiet weather expected through much of the day Thursday, Warming
  trend continues with highs near 90F by Thursday

- Thunderstorms possible Thursday night...with possibly a few
  strong/severe cells north of I-70

- Hot and humid trend starts Sunday

&&

.SHORT TERM (This evening through Thursday)...
Issued at 301 PM EDT Wed Jun 12 2024

Expect quiet weather conditions to persist through the short term
period as surface high pressure remains in control. Latest surface
observations show the aforementioned high near southeastern Indiana
and Kentucky. A weak frontal boundary which moved into far NW
counties this morning has stalled. Earlier thoughts were that
daytime heating over this negligible convergence zone could be
enough to force a few light showers this evening. Confidence remains
very low in this scenario due to weak forcing. Will continue to
keep a dry forecast for this reason, but cannot completely rule out
a few light showers over far NW counties. Plentiful sunshine
combined with increasing southwesterly flow has allowed temperatures
to warm up considerably after a brief cooldown over the past few
days.

Good radiational cooling conditions tonight should allow for
temperatures to fall well into the 60s, possibly upper 50s in a few
spots over far S/SE portions of the area where winds will be nearly
calm. Temperatures will then warm into the upper 80s and possibly
low 90s for some location Thursday with increasing southwesterly
flow and mostly sunny skies. Thankfully dewpoints should remain in
the 50s, but this will likely be the hottest day of the year so far.
Some increase in mid-high clouds may be evident early in the day
from an upper level impulse moving over the northern Great Lakes
Region. Additional clouds are expected towards the evening as a
system approaches. Details on this system will be covered in the
extended period.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 301 PM EDT Wed Jun 12 2024

Thursday night through Saturday...

The long term will begin with a conditional strong to severe t-storm
threat as convection expected to initiate late Thursday between the
Iowa/Illinois region matures to the west of central Indiana Thursday
evening...and then most likely slowly collapses while steadily
crossing Indiana in a southeasterly direction up to pre-dawn hours.
The front end of this convective cluster may bring a few marginally
strong/severe storms, focused near the Upper Wabash Valley...
although stronger gusts could make it as far as the I-70 corridor,
especially if storms started earlier Thursday and/or closer to the
CWA.  Otherwise this should be the most organized rainfall of the
forecast period...with most areas picking up 0.10-0.50 inches along
an overall NW/SE gradient, and perhaps isolated areas up to 0.75-
1.00 inches under one or two stronger/slower cells.  No flooding
concerns following recent drier pattern and rather brief window of
possibly steadier rain.

The remainder of this week will be marked by subtle relief from the
broader trend into a more summerlike pattern...as seasonably strong
Canadian surface high pressure following the Thu night wave...
crosses the Great lakes during Friday-Saturday, bringing lower
heights and H850 temperatures.  Corresponding modest northerly flow
will promote afternoon highs closer to the mid to upper 80s both
days, along with dewpoints that should hang in the 50s...providing
more of a June than July feel to start the weekend under ample
sunshine.

Sunday through Tuesday...

The broad subtropical upper ridge, building northward while slowly
crossing the CONUS through Saturday...will then envelope the Midwest
through at least the first several days of next week.  Latest
guidance is continuing to show stagnant upper troughiness settling
over the northwestern CONUS, which will further promote the ridge
building over the eastern half of North America as well as light to
moderate southerly surface flow into Indiana which will also serve
to boost dewpoints to at least moderate levels.  Surface
cyclogenesis expected to occur from the central High Plains to
western Ontario through the early week may help boost this breeze,
albeit while continuing to advect heat and humidity into the Midwest.

At least a few afternoon showers and t-storms will be possible amid
this hot/humid period when precipitable water values will be around
1.50 to 2.00 inches, although little confidence in location and
timing of any such disorganized convection, with little if any
forcing and any boundaries based on previous days` outflow. Bigger
story will be widespread high temperatures 90-95F, especially Sunday
and Monday when H850 temperatures will approach 20 Celsius.  Higher
dewpoints will promote maximum heat indices in the 90s to possibly
around 100F if any showers/scattered clouds could be dodged.  The
normal max/min at Indianapolis through the long term is 82/63.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 121 PM EDT Wed Jun 12 2024

Impacts:

- None.

Discussion:

VFR conditions are expected through the TAF period as surface high
pressure remains in control. Look for light south/southwesterly
winds to persist throuThursday Through Friday night.

The northwest flow regime will continue aloft through Friday night
which will keep it mostly dry. However, models hint at the potential
for an MCS to move across central Indiana Thursday night. Even if
one doesn`t develop and move through, a cold front will be diving
southeast across the area Thursday night and the combo of lift
associated with that along with models supporting moderate
instability with CAPEs to over 1500 J/kg supports 30+ chance PoPs
Thursday night.

If an MCS would develop, Corfidi vectors favor a southeast moving
complex. Weak surface pressure gradient suggests low level inflow
into the system will be minimal, however 50 knot deep shear and
veering with height to go with the moderate instability supports the
Spc Day2 Marginal and Slight Risks over northern and western parts
of central Indiana with damaging winds and possibly large hail the
main threats.It is too early to diagnose mesoscale details,
including cold pool/shear balance. So, confidence is low on timing
and coverage of convection.

As the surface ridge aligns SW-NE along and south of the Ohio River,
temperatures will gradually warm to near 90 degrees by Thursday.
Meanwhile, potential cold front passage looks like it will result in
Friday being not quite as warm with timing considerations key.
Confidence is trending on the not as warm side.

Saturday Through Wednesday.

The main concern later in the weekend and next week will be the heat
and humidity as an upper ridge builds overhead and then shifts east.
At the same time, southerly low level flow will return to the Ohio
Valley and Great Lakes. The return flow around the high is likely to
result in dew points increasing to the upper 60s and perhaps lower
70s by Monday and with little cloud cover and continued southerly
inflow under the influence of the ridge, temperatures could easily
reach the lower 90s if not Sunday then Monday. With the increased
moisture and instability, can not rule out isolated mainly diurnal
pop ups. Models and ensembles are having problems resolving
northeastward moving upper waves around the back side of the ridge
but there is enough there to at least suggest a few storms can not
be ruled out next week.

This time period will need to the be looked at for potential future
headlines. For now, will broadbrush it in the HWO and keep a weather
story graphic going.gh tonight before increasing on Thursday.

Showers and thunderstorms are possible at all terminals beyond the
end of the TAF period Thursday night. Temporarily poor flying
conditions (MVFR or lower) are possible within any storm.

&&

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

$$

SHORT TERM...Melo
LONG TERM...AGM
AVIATION...Melo