228
FXUS63 KIND 132138
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
538 PM EDT Thu Jun 13 2024

.KEY MESSAGES...

- Thunderstorms likely tonight with a few strong/severe cells
  possible north of I-70.

- Isolated damaging wind gusts are the primary threat, but
  marginally severe hail or localized flooding cannot be ruled out.

- Hot and humid trend starts Sunday...increasing confidence in a
  heat wave continuing into the middle of next week

&&

.MESOSCALE UPDATE...
Issued at 505 PM EDT Thu Jun 13 2024

A narrow low-level theta-e axis interacting with frontal convergence
and subtle ascent/cooling has resulted in thunderstorms forming over
northwest Indiana. Organized multi-cells should move east-
southeasterly. Storms may tend to be outflow dominant given high
LCLs but may balance with shear sufficiently for forward-propagating
segments evolving into the evening. These storms could approach
northern portions of our area, generally north of a Delphi to Tipton
to New Castle line. Limiting factor for intense convection this far
south initially will be a drier low-level environment and
correspondingly weak instability, so we should see a weakening
trend.

Low-level moisture axis will shift southward ahead of the front
though, so additional convection developing further southwest along
the front may impact northwest portions of our forecast area late
this evening. There is some potential for a more organized cluster
of storms evolving from new development over northeast Missouri and
southeast Iowa to reach west-central Indiana late evening/overnight.
Primary threats with the most intense convection this evening and
tonight will be strong to isolated damaging wind gusts.

&&

.SHORT TERM (This evening through Friday)...
Issued at 302 PM EDT Thu Jun 13 2024

Current satellite imagery shows quiet weather conditions across
central Indiana with mostly clear skies as surface ridging remains
in place. This will change towards the evening and overnight hours
once a cold front begins to approach the area. Increasing
southwesterly flow ahead of this front has already warmed
temperatures well into the 80s. Some locations could potentially
reach the low 90s over the next few hours.

Scattered to numerous thunderstorms are expected to develop across
IL this evening along the aforementioned cold front. These storms
should grow upscale due to linear forcing and strong DCAPE for cold
pool generation/growth before moving towards the area. The MCS will
likely begin weakening as it enters Indiana as guidance shows much
weaker deep-layer shear with eastward extent. However, sufficient
instability may help the cluster of storms maintain enough intensity
to produce isolated damaging wind gusts if a strong cold pool can
develop, mainly across NW counties. Marginally severe hail cannot be
completely ruled out, but the linear nature of these storms should
limit the overall threat. Localized flooding will also be a threat
with the potential for training storms. Latest trends have been for
a slower arrival thus POPs were delayed slightly. Rain chances
increase quickly after 10pm from NW to SE.

The front will move out of the region late tonight allowing for dry
conditions to return. Expect surface high pressure to build in on
Friday with quiet weather conditions. Weak cold air advection and
some lingering clouds early in the day should lead to slightly
cooler temperatures.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 302 PM EDT Thu Jun 13 2024

Friday night through Monday...

The long term will begin with the final transition from early summer
warmth to mid-summer heat...and follow with prolonged heat and
increasing humidity...in what may be the most pronounced heat wave
*in June* for the entire central Indiana region since 2012.  The
first portion of the building long-wave, subtropical upper ridge
will slowly cross the CONUS through early next week...with any very
small embedded waves lifting from the central Plains to the Great
Lakes. H500 heights over the local region will slowly increase to
588-590 dm for the Sunday-Monday period.  Mid-levels will meanwhile
stay dry promoting few clouds and ample insolation during day times.
Broad surface high pressure originally positioned mainly north of
the CWA will expand while stalling under the stacked ridge to our
east and then southeast...promoting southerly/SSW surface winds by
Sunday, which may gust up to 15-20 mph by Monday.

This will all translate to near normal temperatures for the Friday
night to Saturday night period under the passing northern high...
with lows around the low 60s and highs Saturday near the mid-80s
amid the light easterly flow.  Noticeable transition on tap for
Sunday when sun and warm advection are staked to boost all corners
of the region to 90-95F...which will be the first 90F+ day for many
locations.  Slightly hotter conditions are possible Monday per
better WAA and morning lows likely starting about 10 degrees higher.
Higher confidence in moderate humidity for Monday following longer
fetch off the Gulf...bringing the potential for triple-digit heat
index values to much of the region.  Can not rule out a stray shower
Monday but expect the generally capped profile to continue rain-free
conditions for most spots.

Tuesday through Thursday...

Latest guidance is indicating increasing confidence in a pronounced
upper trough over the northwestern CONUS/Canadian plains into the
middle of next week, which will help to boost the next bubble of the
subtropical H500 ridge over the Midwest, with perhaps a 595 dm
height reaching Indiana by the end of the long term.  The broad
surface ridge is progged to remain over or to the east of the Mid-
Atlantic, maintaining the southerly flow into central Indiana.
Higher, yet probably not oppressive dewpoints should hold overnight
minimums to the 70s...and, when coupled with mainly FEW/SCT clouds,
promote diurnal spreads approaching 20 degrees...which should
continue the late-June heat wave through at least Thursday.

Any potential relief from 90F+ temps would be limited to greater
cloud cover should the increasing deep moisture be able to organize
above the cap or getting caught under what should be a few showers
and a stray thunderstorm through the mid-week.  Unfortunately given
lack of any approaching wave or forcing confidence in either
opportunity for any location will be low.  Any breakdown in the
strong and broad ridge will likely follow the end of the long term.

Indianapolis has only reached 95F as early as June 17 on 11
occasions since 1871...and only twice since 1952 (95F on both
6/4/2011 and 5/28/2018).
Indianapolis has only observed five days 92F+ during 6/1 - 6/20 on
11 occasions...and only twice since 1954 (6 in both 1988 and 1994).

&&

.AVIATION (00Z TAF Issuance)...
Issued at 538 PM EDT Thu Jun 13 2024

Impacts:

- Thunderstorms 03z-09z

- Brief MVFR stratus as front moves out Friday morning/midday

Discussion:

Few changes to the 00z TAF. Refined timing slightly and further
adjustments/amendments may be needed. Confidence is highest for
thunderstorms at KLAF and KHUF, and lowest at KBMG. Brief
strong/variable winds near thunderstorms can be expected.

Low level moisture may result in scattered to broken clouds that may
briefly bring us into MVFR. This should improve by early afternoon.

&&

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

$$

MESOSCALE...BRB
SHORT TERM...Melo
LONG TERM...AGM
AVIATION...BRB