764
FXUS63 KIND 041417
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1017 AM EDT Sat May 4 2024

.KEY MESSAGES...

- Warm with isolated to scattered showers and thunderstorms today
  into tonight. Severe storms are not expected.

- Isolated flooding threat Monday.

- Growing confidence in the potential for a few rounds of severe
  thunderstorms Tuesday through Wednesday.

&&

.FORECAST UPDATE...
Issued at 1017 AM EDT Sat May 4 2024

Showers and non-severe thunderstorms continue across Southeastern
Indiana this morning, so have gone ahead and raised PoPs for areas
south and east of Indianapolis through the rest of the morning
hours.

Weak upper wave and associated surface reflection within a
southwesterly flow pattern are providing just enough lift to spark
off a few showers and thunderstorms this morning. Latest ACARs
soundings from Cincinnati and Louisville show a saturated 0-4km layer
with upwards of 700-900 j/kg of CAPE across the region. Low level
shear is very weak, so not expecting any severe weather with this
convection, mainly garden variety showers and storms with lightning
and brief periods of heavy rain expected. This wave and associated
energy will slowly pull off to the northeast through the day,
keeping the best chance for any showers or storms in Eastern and
Southeastern Indiana. Lower confidence exists with how far west
storms may form today and if they could reach Indianapolis. Most
short term hi-res guidance keeps everything just east of Marion
County through the afternoon; however with such a moist, unstable
environment, it is not out of the question for a stray shower or
storm to develop further west towards the Indy Metro area. Lowered
highs for Eastern Indiana to remain in the lower to mid 70s with
increased clouds and convection around. Along and west of the I-65
corridor, less clouds will allow for more boundary layer heating and
deeper mixing to support highs reaching the 80 degree mark.

&&

.SHORT TERM (Today and tonight)...
Issued at 300 AM EDT Sat May 4 2024

Another warm and somewhat humid day and evening is expected across
central Indiana today into tonight, as weak low pressure remains in
the region and a couple of subtle upper level impulses impinge upon
the area.

Despite these features and a relatively moist airmass, modest
instability and weak deep layer shear will limit intensity and
coverage of showers and thunderstorms to isolated-scattered, with
the highest chances in the east nearer the better moisture, a weak
boundary, and where weak to non-existent capping will exist, in
contrast to the western and northwestern portions of the area, where
a modest capping inversion centered around 700 mb looks to remain in
place much of the day.

Will carry 20-40 percent PoPs across much of the area save the
northwest today, slowly working them back westward as winds shift
and advect the deeper moisture a bit further back into central
Indiana today.

Aforementioned parameter space weaknesses should limit threat to
brief heavy downpours and lightning, with no substantial threat for
severe storms.

Additional convection associated with an approaching upper level
impulse may move through the area tonight, but would likely be
weakening diurnally as it does so. Will carry slight chance to low
chance PoPs tonight.

Temperatures should be a bit warmer today per low level thickness
progs, and blending in MOS and NBM yields mid 70s to low 80s across
the area, which appears quite reasonable. Overnight lows will depend
significantly upon evolution of convection that may move into the
area, and resultant cloud cover, but guidance is fairly tightly
clustered, and made only minor adjustments to yield mid 50s to low
60s across the area.

&&

.LONG TERM (Sunday through Friday)...
Issued at 300 AM EDT Sat May 4 2024

Sunday and Monday.

The long term continues to look rather active for the Ohio Valley. A
steep ridge access over the EC has kept broad S/W flow over the
region. This in combination with consistent troughing to the west
will maintain the creation of waves/lift over the central US

Sunday will be no exception, beginning with a departing mid level
wave Sunday morning. Any remaining convection should be weak by
Sunday morning, but lingering showers are possible until high
pressure builds in beneath AVA. During the day on Sunday, another
shortwave is expected to develop over the mid-Mississippi Valley,
centered within the diffluent region of the subtropical jet. This
should push E/N into the Ohio Valley late on Sunday. Uncertainty
is still high if the northern periphery of this wave will be
enough to overcome developing low level high pressure, and
subsequent shower/storm development. Regardless, instability
should remain modest in the afternoon and evening (1000 J/kg), and
isolated pop-up thunderstorms will be a threat. Will continue to
monitor for the potential of a more consistent source of lift and
resulting greater coverage, but for now this looks unlikely.

The greater source of lift within the aforementioned wave looks to
arrive late Sunday night through Monday, with greater than 70% PoPs
by Monday afternoon. The overall parameter spacing on Monday does
not support organized convection, but the deeply saturated profile
along with long, "skinny" CAPE should lead to highly efficient rain
producers. A single storm likely wont create flooding issues, but if
multiple cells pass over similar areas, flooding concern will likely
become heightened.

Tuesday Through Thursday.

The next round of unsettled weather will push into the region
shortly after, with another trough, albeit deeper, over the Inter-
Mountain West by Tuesday. This time around, a more organized low
pressure system is expected to develop, rapidly deepening as it
reaches the Great Plains, pointing a strong westerly mid to upper
level jet at the Midwest. As the low develops, convergence east of
the low should create a weak warm-frontal region and associated
isentropic ascent. This lift is expected to reach the Great Lakes
and Ohio Valley sometime Monday night into Tuesday, leading to
showers and some elevated thunderstorms.

Following this warm front passage, central Indiana will be within a
highly unstable environment with a strong mid and upper level jet
aloft. Uncertainty remains high on timing and specifics, but
confidence is growing on a organized severe threat across the Ohio
Valley Tuesday and Wednesday, primarily focused on the potential for
a few quick passing shortwaves attached to the prior mention jet
streak.

The thunderstorm and severe threat should decrease late week as AVA
and modest CAA returns leading to high pressure and a drier overall
airmass.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 630 AM EDT Sat May 4 2024

Impacts:

- MVFR ceilings/visibilities for at least brief periods at all sites
  late tonight through daybreak.

- Low chance for isolated convection Saturday (Primarily at KBMG)

- MVFR ceilings and scattered showers possible tonight.

Discussion:

As skies clear from west to east overnight, some fog has developed
at all sites for at least brief periods. Will carry prevailing MVFR
at all outlying sites (IFR at BMG) and TEMPO MVFR at IND. These
conditions may persist in some areas into mid morning before
returning to VFR.

There will be a low chance for showers and isolated storms today,
but too low for inclusion in the TAF except for KBMG at this time.
More showers with MVFR ceilings will arrive overnight.

Winds will shift significantly through the period, beginning
northeasterly and becoming southerly/southwesterly late in the
period. Another wind shift is expected overnight towards NW.
Sustained winds will remain below 10KT throughout.


&&

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

$$

UPDATE...CM
SHORT TERM...Nield
LONG TERM...Updike
AVIATION...Updike