558
FXUS63 KIND 140715
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 CONUS 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. The hottest days of the extended look to be Monday through
Thursday, where high temperatures could reach or exceed 95 degrees.
Historically, the NBM has been too hot with highs in the long term,
so have kept max temps around the NBM25th percentile for now.
However, this still keeps highs in the 95-98 degree range for the
entire region Monday, and the 92-96 degree range the rest of the
week.

During this time period, strong moist air advection north on the
west side of the low level ridge will bring moist gulf air into the
region, with anomalously high PW and dew points hovering around 70
degrees. Heat indices at or above 100 degrees are possible during
peak heating of the day Monday through Friday.

Any potential relief from 90F+ temps would be limited to greater
cloud cover should the increasing deep moisture be able to organize
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. Monday and Tuesday
afternoon look have at least a 15-20 percent chance of a rogue
shower or thunderstorm developing. The low level jet increases to
the west, but may be strong enough over Central Indiana around 10-20
kts to support a thunderstorm in such a hot humid environment with
convective temperatures likely being met. Adding 15-20 PoPs Monday
and Tuesday afternoon and evenings for now, but confidence remains
low on coverage and exact location of development. Most places will
likely remain dry through next week, so do not plan on a rogue
thunderstorm providing much relief.

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