-- Discussion containing changed information from previous version are highlighted. --
799
FXUS63 KIND 211802
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
202 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

&&

.FORECAST UPDATE...
Issued at 1011 AM EDT Fri Jun 21 2024

-Patchy alto-cu and slightly quicker warming that originally
 expected

The bulk of the forecast has remained similar but a few changes have
been made to temperatures and sky cover to reflect observations. The
agitation within the altocumulus above the metropolitan areas
showcases the instability above the capped boundary layer currently,
with diurnal cu expected to develop shortly after convective
temperatures are met early this afternoon. Current expectation is
for cloud cover to be around 30-50%.

Temperatures have quickly warmed this morning, with areas already in
the mid 80s as of 14Z. This should continue throughout the morning,
and likely will be further reinforced by afternoon mixing and slight
drying of the near surface layer. The forecast high of 94 for
Indianapolis has been kept, but this could be a degree or too low
given current observations and the magnitude of mixing this
afternoon. Will continue to monitor and adjust as needed.

&&

.SHORT TERM (Today and tonight)...
Issued at 259 AM EDT Fri Jun 21 2024

Current weather...

A sprawling, elongated mid-level (500 mb) ridge axis centered across
the lower OH and TN Valleys this morning will continue to control
our central IN weather today and tonight, and into Saturday as well.
The ridge is providing overall subsidence across our area at this
time, with a mostly clear sky. Early morning temps should bottom out
in the upper 60s and lower 70s, several degrees above normal lows in
the lower-mid 60s for today, the first full day of summer.

More heat today...

With the ridge anchored in place, today`s weather will be similar to
yesterday. Maximum temps yesterday afternoon generally ranged from
90-94 at reporting stations, and this should again be the case today
with highs in the toasty lower-mid 90s. These high temps will be
about 10 degrees above normals in the lower-mid 80s for June 21.

Surface dewpoints also are likely to trend similarly to yesterday,
i.e., be maximized near/around 70 in the morning hours, but with
modest mixing and dry air mix down this afternoon, drop into the mid-
upper 60s during the time of peak heating. Thus, maximum heat
indices should remain generally in the mid-upper 90s (vs. 100+ if
dewpoints would remain higher). While max indices remain several
degrees below advisory criteria, the daily duration of the heat is
becoming a concern, especially for those groups (elderly, very
young, those without access to AC/cooling, etc.) who may be more
vulnerable. We will continue with our Special Weather Statement for
today for now to highlight the heat, with appropriate messaging to
take necessary precautions, including drinking sufficient non-
alcoholic liquids, wearing lightweight clothing, and limiting
extended outdoor exposure during the mid/late afternoon if possible.

Other weather conditions today and tonight...

Skies should be mostly sunny to partly cloudy today, with occasional
scattered mid/high clouds this morning, and some diurnal cumulus
this afternoon. However, general subsidence and limited moisture
should preclude any shower development. Then mostly clear again
tonight with lows Saturday morning in the upper 60s to mid 70s.

&&

.LONG TERM (Saturday through Thursday)...
Issued at 259 AM EDT Fri Jun 21 2024

Another hot day Saturday...

On Saturday, the mid-level ridge will be pushed south across the TN
and lower MS Valleys as modest increasing westerly 500 mb flow
develops across Indiana in advance of a broad shortwave trough over
the central/northern Plains into the western Great Lakes states.
However, in general the ridge should continue to keep a stronghold
on our central IN weather Saturday with overall hot, dry weather.
Nevertheless, with slightly lower suppressing heights aloft and with
a modest increase in low-level SW moisture advection, cannot
preclude an isolated shower or storm Saturday afternoon, but any
rain would be spotty, brief, and highly diurnal in nature. The main
story will be the continued heat as afternoon maximum temps again
peak in the lower-mid 90s. Coupled with expected dewpoints in the
mid-upper 60s (humid, but not oppressive), heat indices should again
top out in the mid-upper 90s.

Rain chances late Saturday night into Sunday...

Associated with the trough aloft to our N and W, forcing along a
cold front should ignite a line of scattered to numerous
thunderstorms Saturday afternoon and evening from the Great Lakes SW
into northern and central IL. Ahead of the line, a relatively narrow
plume of stronger moisture transport should elevate precipitable
water (PW) values to around 2 inches as the line propagates SE into
northern, then central IN overnight Saturday night into early Sunday
morning. While diurnal low-level instability will wane with only
modest elevated lapse rates, the convective cold pool and general
forcing associated with the line should keep it together long
enough to produce scattered to numerous showers and storms across
central IN, especially northern counties. Rainfall amounts should
not be too high though given fast system movement and an expected
general slow decreasing trend in storm intensity with time.

Frontal passage Sunday afternoon...

As any morning showers and associated outflow boundary pass to our S
and E by Sunday afternoon, the actual cold front will lag and drop
across central IN in the afternoon. There could be enough airmass
recovery and frontal forcing for isolated afternoon thunderstorm
development, mainly across southern parts of central IN. The worst
of the heat should be knocked south too with afternoon highs from 85-
90 to perhaps lower 90s in our far SW counties ahead of the front.

Drier Sunday night and Monday...

Post-frontal, conditions will dry out Sunday night and Monday as
weak surface high pressure and lower surface dewpoints advance
across Indiana. It will still be quite warm Monday afternoon with
highs in the mid 80s to lower 90s, but lower humidity values will
keep conditions more tolerable.

Storms, perhaps organized, return Tuesday into Wednesday...

The tranquil, drier weather will be short-lived, plus the heat will
return in earnest on Tuesday. This time period should feature W to
NW flow aloft across the mid/northern MS Valley across the Great
Lakes and OH Valley. Shortwaves embedded in this flow could set up
MCS activity late Monday night well to our N and W, but more likely
late Tuesday and especially Tuesday night into Wednesday. A nice
instability gradient develops Monday night to our W, with an
unstable inflow into the western Great Lakes. Models are not bullish
with QPF in this area then, but the pattern suggests possible MCS
development well N and W of us within the gradient zone, which if an
MCS develops could clip our northern counties late Monday night or
Tuesday morning, although the forecast reflects dry weather at this
time.

On Tuesday, a hot and breezy SW low-level flow develops over central
IN. Assuming no interference from any isolated convection or
convective outflow, the pattern suggests perhaps the hottest day so
far this season, with highs potentially in the mid and upper 90s,
especially over our SW counties. Coupled with dewpoints in the lower-
mid 70s, heat indices would easily top 100 by several degrees.

Isolated storm development may occur Tuesday afternoon, but the
pattern favors possible organized MCS development Tuesday evening or
night (as supported by multiple models and successive runs of the
same models) somewhere just to our N and W, with SE propagation
across central IN and points W over IL. Models show moderate to
strong instability and elevated steep lapse rates, along with modest
shear to support storm organization. This is still well out in time,
but something to keep an eye on. Bottom line, expect potentially
very hot conditions Tuesday followed by organized thunderstorms late
Tuesday night, possibly continuing or redeveloping Wednesday.

Cooler and drier Thursday into Friday...

A long way out in time, but current projections suggest another
break from the heat and storms may occur Thursday into Friday, with
temps closer to seasonal normals. But more should could return by
next weekend.

&&

.AVIATION (18Z TAF Issuance)...
-- Changed Discussion --
Issued at 202 PM EDT Fri Jun 21 2024

Impacts:
- VFR conditions expected through the TAF period.

Discussion:

Conditions will remain VFR through the entire forecast period as
high pressure aloft continues to keep tranquil weather at all TAF
sites.

Light surface winds out of the W/SW will continue through the
evening before become calm overnight. Winds will pick up again
tomorrow with gusts potentially in the mid to late afternoon.
Sct/bkn mid-level clouds around 5-6 kft this afternoon will
dissipate this evening, with sct mid-high clouds overnight
-- End Changed Discussion --

&&

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

$$

UPDATE...Updike
SHORT TERM...Funk
LONG TERM...Funk
AVIATION...Updike