686
FXUS63 KIND 140702
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
302 AM EDT Fri Jun 14 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms through daybreak

- A few showers or storms over southeast Indiana this afternoon

- Dry and seasonable tonight and Saturday

- Hot and humid trend starts Sunday...increasing confidence in
  potentially hazardous heat into next week

&&

.SHORT TERM (Today and Tonight)...
Issued at 302 AM EDT Fri Jun 14 2024

Convection that has moved across the forecast area since late
Thursday evening is finally weakening as it moves out of our eastern
counties as of 0630Z. Despite the drier air and lack of extensive
instability over much of the region as the storms moved in...a
cluster of stronger cells produced pockets of likely 50-60mph winds
tracked from near Crawfordsville southeast across the southwest Indy
metro and into Johnson County before weakening. A noted rear inflow
jet was a contributor to these stronger winds surging out at the
surface as the storms tracked southeast. Temperatures were currently
in the mid and upper 60s early this morning with additional
scattered convection moving into the northern Wabash Valley.

Scattered convection will persist over the next several hours with a
low risk for a few showers or storms across southeast portions of
the forecast area even into this afternoon as the weak frontal
boundary lingers across southern Indiana. A large area of high
pressure will expand into the region from the north by late today
and bring seasonable temperatures into the first part of the
weekend...before the hottest air of the season arrives Sunday into
next week.

This Morning

Additional convection continues to fire across central Illinois and
the CAMs are not doing a great job of capturing this. Appears the
main catalyst for the renewed convective development is the presence
of subtly stronger flow at 850mb with westerly winds near 30kts
feeding into the showers and storms. With elevated instability in
place and the stronger flow at 850mb expected to persist through
daybreak...expect scattered convection to migrate into the forecast
area and gradually sag southeast over the next few hours. Locally
heavy rainfall will be the primary impact and considering the
forecast going forward into next week...any additional rainfall will
be welcome through later this morning. The weakening and veering of
the 850mb flow as the morning progresses will largely diminish
activity.

This Afternoon and Tonight

The front will be positioned somewhere across the southern half of
the forecast area by the afternoon and despite better forcing aloft
along the boundary to our east...enough instability and lift in the
vicinity of the front to generate a few showers and perhaps a couple
thunderstorms over southeast counties through late afternoon.
Further north across the forecast area...a noted surge of drier air
and subsidence in tandem with a well mixed boundary layer will
support some wind gusts through the afternoon with mostly sunny
skies developing.

The remnant boundary will drop south of the Ohio River tonight with
high pressure from the north taking over across central Indiana.
Skies will be clear overnight with N/NE winds bringing a refreshing
airmass as dewpoints fall back into the 50s.

Temps...despite the passage of the front through the afternoon and
the progressively drier airmass arriving in its wake...low level
thermals are supportive of highs close to if not just a few degrees
cooler than Thursday. Expect mid and upper 80s across the forecast
area. Lows tonight will be comfortable...falling into the upper 50s
and lower 60s.

&&

.LONG TERM (Saturday through Thursday)...
Issued at 302 AM EDT Fri Jun 14 2024

Saturday through Next Week

**Increasing confidence in an extended period of very hot and humid
conditions Sunday through much of next week**

Looking back at maximum high temperatures for the month of June
across Central Indiana, climatology shows that it`s relatively rare
to see highs exceed 95 degrees. And 3 or more consecutive days at or
above 95 degrees in June is exceedingly rare for Central Indiana,
with only 3 occurrences of that happening in June at KIND
(Indianapolis International Airport). The upcoming weather pattern
does support consecutive days with highs potentially reaching and
exceeding 95 degrees for all of Central Indiana in addition to warm
nights in the 70s and humid conditions.

Saturday will likely be the "coolest" day over the next week with
highs in the mid 80s as the heat dome and best warm air advection
still remain to the west across the Plains.

500mb ridging strengthens over the south on Sunday with 500mb
heights reaching 593dm over Georgia. Through the rest of the week,
upper ridging slowly shifts to the northeast while strengthening with
500mb heights potentially reaching 600dm, indicating an
anomalously strong ridge taking hold of the eastern half of the
country. The low level ridge and surface high pressure remain east
of Indiana during this entire period keeping strongest warm air and
moist air advection right over the Ohio Valley. One thing to note,
with the center of the high pressure over the NE Conus and Atlantic,
the best subsidence and associated low level subsidence inversions
will likely remain to the east. Forecast soundings Sunday into early
next week show very steep low level lapse rates and deep mixing
heights, further increasing confidence that high temperatures could
exceed 95 degrees, despite such a humid airmass.

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.


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 (06Z TAF Issuance)...
Issued at 1115 PM EDT Thu Jun 13 2024

Impacts:

- Thunderstorms around until about 09z

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

Discussion:

Thunderstorms are expected to decrease by the predawn hours with
impacts to TAF sites possible until then, including gusty winds and
brief visibility reductions in heavy rain. Ceilings could lower due
to post-frontal stratus at least briefly. VFR conditions will return
by early afternoon and prevail through the remainder of the TAF
period.

&&

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

&&

$$

SHORT TERM...Ryan
LONG TERM...CM
AVIATION...BRB