636
FXUS63 KIND 031843
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
243 PM EDT Wed Jul 3 2024

.KEY MESSAGES...

- Scattered thunderstorms this evening, a few storms may pose a
damaging wind threat in South Central Indiana

- Additional rain and storm chances Thursday morning and again late
Thursday night into Friday

- Expected lull in between rounds of storms during the afternoon and
evening for 4th of July

- Dry conditions and less humid late Friday through Sunday...highs
around 80F on Saturday

&&

.SHORT TERM (This evening through Thursday)...
Issued at 243 PM EDT Wed Jul 3 2024

Latest satellite imagery shows widespread high level cloud cover
across the western and northern 2/3 of Central Indiana, greater
coverage than what previous guidance has suggested. The SE quadrant
of Central Indiana currently has a healthy cu field developing due
to greater boundary layer heating and less upper level cloud cover.
Current frontal boundary extends W-E across the state from around
Danville, IL to Muncie with SW surface flow and dew points in the
lower 70s south of the front. While high clouds have resulted in
less boundary layer heating and subsequent destabilization, still
expecting scattered showers and thunderstorms to develop later this
afternoon and evening. Latest IND ACARs sounding does show weak
capping in place and poor mid level lapse rates, which may limit the
overall coverage of storms later. The best environment for stronger
to potentially severe storms is across far SW and SE Indiana, where
greater instability and steeper lower level lapse rates are present.
The Louisville ACARs sounding is likely more indicative of the
environment in Southern Indiana showing much steeper low level lapse
rates near 7.0 C/km, CAPE over 1000j/kg and DCAPE values exceeding
800 j/kg. LLJ aloft is weakening with 0-3km shear at or under 25 kts
across the state, not very supportive of sustained, and organized
updrafts, but the thermodynamic profile does support an isolated
damaging wind threat from wet microbursts. Expect scattered
convection to initiate along and south of the I-70 corridor over the
next few hours with the threat continuing through around 03z
tonight.

Later tonight, a secondary low from the SW will begin to develop,
helping re-establish a moist warm sector over southern portions of
the state. Depending on where the aforementioned frontal boundary
sets up, potential is there for low clouds and patchy fog along and
north of this boundary near dawn on Thursday. Best chance for lower
clouds and patchy fog is along and north of I-70. Hi-res guidance
does indicate an overnight complex of showers and storms developing
in Missouri and pushing eastward into South Central Indiana around
dawn as well. Confidence is low on this as guidance tends to poorly
perform in scenarios where there are multiple rounds of showers and
storms with weak synoptic scale forcing. Keeping highest PoPs
overnight in Southern and SW Indiana for now, but will have to
closely monitor upstream trends tonight.


.Tomorrow...

The first half of the holiday looks to be relatively cloudy, humid,
and warm with the threat for showers and storms. Frontal boundary
from the previous day remains draped across the region with the
potential for a convective complex during the morning hours.
Typically these are in a weakening phase as they approach Indiana;
so confidence remains low in how widespread shower and storm
activity will be around sunrise. Latest guidance does show the best
chance for a morning round of precipitation along and south of the I-
70 corridor. The main threats with any morning convection will
likely be heavy rain and flooding for areas that see repeated
storms, especially as precipitable water values will be near or over
2.0 inches.

Guidance indicates subtle ridging in the mid levels during the
afternoon and evening hours ahead of an approaching low over the
Upper Midwest. With this in mind, despite a frontal boundary near
the Ohio River, mid level drying and subsidence may work to inhibit
convective development during the latter half of the day tomorrow.
Still expecting low and high level clouds to stick around through
the day, with a few peaks of sun towards the evening hours.
Confidence is lower if clouds will break up; so keeping forecast
high temperatures below guidance in the lower 80s for Central and
North Central Indiana and mid 80s for Southern Indiana closer to the
front. Despite "below average" highs for the 4th of July, humidity
will be rather oppressive, even for this time of year, with a
tropical like airmass in place.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 243 PM EDT Wed Jul 3 2024

Thursday Night through Friday night...

Despite not having the greatest confidence in timing or location of
any organized showers/t-storms Thursday night...latest guidance is
indicating late Thursday`s modest ridging should continue through
the evening hours, ahead of low pressure slowly approaching from the
northwest.  Suspect widely scattered showers to return later during
the overnight, although modest CAPE and unimpressive mid-level lapse
rates should prevent any severe weather.  Any heavier rainfall in
stronger showers/isolated t-storms is not expected to be widespread,
although much of the area could see at least brief rain late
Thursday night.

Surface low pressure over the Upper Midwest will strengthen while
slowly crossing the northern Great Lakes through the late week.  The
supporting upper wave should deepen while crossing the northern
Mississippi Valley...with the whole system dragging its north-south
cold front across central Indiana during the day Friday.  So far
appears moderate confidence that corresponding scattered showers
and t-storms would be sub-severe Friday with better instability and
deep moisture departing east just before better shear arrives with
the upper wave.  Post-frontal WSW breezes should gust to 20-25 mph,
especially north of I-70...dropping humidity to more reasonable mid-
summer levels by evening.  Friday night will be dry with a return to
seasonable temperatures as light to moderate breezes drop dewpoints
towards 60F.

Saturday through Monday...

Overall lower heights across much of the CONUS are expected between
short wave troughs over both the Great Lakes from the slowly-
departing late-week system and a plunging short wave over the
northern High Plains.  In between weak yet broad surface high
pressure will cross from the central High Plains to the Mid-
Atlantic.  Dry conditions and slightly lower dewpoints near 60-65F
should therefore prevail over the region through Sunday...before
more southwesterly flow around the Sunday night-Monday timeframe
returns seasonably moderate humidity, clouds, and likely a few
showers with perhaps isolated thunder.  Saturday and Saturday night
should be the mildest/coolest periods of the long term with readings
about 5 degrees below normal...before seasonable warmth returns to
start next week.

Tuesday and Wednesday...

A rather broad trough slowly crossing interior/northern North
America will drag its southern portions into the Midwest for the mid-
week. Modest westerly surface flow under lower heights and lower
H850 temperatures should be the rule...along with a trend to lower
rain chances as corresponding surface high pressure arrives from the
north-central CONUS.  Expect ample sunshine and limited cold air
advection to bring near to slightly below normal temperatures, with
widely scattered diurnal showers/storms possible from the passing
wave`s weak forcing.  The normal max/min at Indianapolis through the
long term is 85/66.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 131 PM EDT Wed Jul 3 2024

Impacts:

- SCT t-storms along and south of I-70 18z-03z

- Potential for MVFR cigs and vis near sunrise with additional rain

- Southwesterly wind gusts up to 20 knots through this evening

Discussion:

A weak front just north of I-70 will be the focus for shower and
thunderstorm development this afternoon and evening across Central
Indiana. Convection has already been observed along this front in
North Central Indiana but has since moved away from any TAF sites.
Latest satellite imagery does show a cumulus field developing along
and south of the I-70 corridor. Expect continued growth of cumulus
clouds over the next couple hours with showers and a few storms
developing along I-70. Coverage is expected to increase later this
evening and push southward toward KHUF and KBMG. Brief periods of
heavy rain, lightning, gusty winds, and MVFR cigs and vis are
expected with any storm. Outside of any storm, southwesterly to
westerly winds may gust up to 20 kts at times south of the front,
with winds becoming WNW behind the front at 10 kts or less.

Expect convection to wane shortly after sunset with a lull in the
precipitation overnight. Potential is there for patchy fog to
develop as winds subside overnight and surface temps fall near the
dew point. Not expecting anything widespread, but MVFR or lower cigs
are certainly possible, especially in areas just north of the front,
mainly KLAF. Hi-res guidance does indicate another complex of
showers and storms possibly pushing in during the 09-12z timeframe
along and south of the I-70 corridor once again. Lower confidence
exists as guidance tends to poorly handle timing and placement of
multiple rounds of convection, especially more than 12 hours out. But
will still put the threat for showers and MVFR cigs in the TAFs
during this period as lower clouds and patchy fog may still develop
even if this second round of convection holds off.


&&

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

$$

SHORT TERM...CM
LONG TERM...AGM
AVIATION...CM