814
FXUS63 KIND 161708
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
108 PM EDT Tue Jul 16 2024

.KEY MESSAGES...

- Thunderstorms with strong winds possible early today, mainly
southwest of Indianapolis

- Flash flooding possible across portions of the area today
and tonight, especially along and south of Interstate 70

- Dry weather along with a break from the heat and humidity Thursday
through this weekend

&&

.FORECAST UPDATE...
Issued at 1111 AM EDT Tue Jul 16 2024

ACARS shows an overturned thermodynamic environment in the wake of
the MCS. The trough is still back to the west and will encourage
modest southwesterly flow and moisture return, but the core of the
rich low level moisture will likely remain south of the area near
and south of the residual cold pool. There should be a tendency for
propagation of upstream convection to be influenced largely by the
low-level theta-e gradient, so a more southeastward propagation is
expected. As mid-high level clouds from remnant MCS decrease and
surface heating/destabilization continue at least isolated to
scattered convection should reform by late afternoon into the
evening.

&&

.SHORT TERM (Today and tonight)...
Issued at 254 AM EDT Tue Jul 16 2024

One final day in the very humid and at least marginally hot
subtropical air mass will promote continued rain and storm chances
ahead of and following a long-needed midday cold frontal passage.
Following several rounds of isolated to scattered severe weather
through the early week...one final opportunity for organized
strong/severe storms early today will accompany a cluster of storms
approaching the region from central Illinois as of 230A this
morning.  A more marginal threat of stronger storms embedded within
increasing rain chances through PM hours is expected...courtesy
adequate instability with mediocre lapse rates, and weak vertical
wind shear through at least most of the day.

The greater hazard will be flood potential amid increasing precip
water and convergence ahead of the approaching boundary...with pwat
values boosted above 2.00 inches during midday hours for all but far
northern counties, and perhaps even briefly 2.50 inches over
southwestern zones which would be more an a 1.00 inch anomaly. What
should be a west-east band of best convergence is expected to align
with mid-70s dewpoints by midday before trending southward through
the region into the evening.  Resultant precipitation through
Tuesday night should reach 1.00 to 2.00 inches in areas, with the
potential for localized maxima of 2.00 to 4.00 inches under the most
impressive bands of training rain.  Therefore have continued two-
tier Flood Watch for all of CWA`s 39 counties...through 200PM
near/north of I-70 corridor...and through 200AM Tuesday night for
the region`s two southern tiers of counties.

A secondary concern through the short term will be one final day of
marginal heat ahead of the approaching front...lead by mid-70s
dewpoints that, when coupled with low 90s in the afternoon across
southern zones...will promote a few hours of heat indices at or just
above 100F.  This concern is somewhat conditional with generally BKN
mid-level decks expected to prevail over southern counties, which
may hold readings under 90F, and therefore heat indices under
100F...so have held off from issuing another SPS for this sub-
Advisory threat.

Turning to Tuesday night, north of I-70 and the continuing heavy
rain/flooding potential rain chances should slowly decrease as
slightly cooler ad drier air begins to enter the region.  Fog
formation will certainly be a threat over any areas where heavier
rain falls, although low certainty so far on location and timing
of any reduced visibility. Temperatures will have one final
near/above normal day Tuesday with mid to upper 80s the general
rule, and perhaps low 90s across the southern tier...with lows in
the upper 60s to around 70F then expected Tuesday night. More
noticeable drop in humidity and readings will occur early in the
long term following the frontal zone`s passage.

&&

.LONG TERM (Wednesday through Monday)...
Issued at 254 AM EDT Tue Jul 16 2024

Big changes are in store for the long term as surface high pressure
moves in, in the wake of a cold front. This will bring in a much
drier and not as hot airmass starting Thursday. Wednesday is more up
in the air as a cold front is expected to be over south central
Indiana, perhaps even south of the CWA by 12z. That said, the dry
air will take awhile to move in and with a sharp upper trough over
the western Great Lakes and upper Midwest and lingering strong
instability, will keep thunderstorm chances going with 40-60% PoPs
over our far southern tier tapering off to 20% PoPs over our far
northern tier, further away from the front.

Thursday looks to be the most pleasant day a dry column per
soundings supporting near full sunshine. Meanwhile,  low level
thermals support well below normal temperatures with highs only in
the 70s and combined with dew points in the 50s, it will be a
welcomed respite from the heat and humidity. As the airmass
gradually modifies with high pressure overhead, temperatures will
creep back up to near normal late in the weekend or early next week.
The next chance of convection looks like it will hold off until next
week as the high moves off to the east allowing for a gradually
return of southerly flow to potentially interact with an upstream
broad trough.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 108 PM EDT Tue Jul 16 2024

Impacts:

- VFR Conditions this afternoon.

- Afternoon TSRA possible at HUF and BMG.

- Overall TSRA possible at all Taf Sites, best chances south.

- Any TSRA will result in brief MVFR to IFR conditions.

Discussion:

Convective complex over southern IL is expected to remain southwest
of the TAF sites this afternoon. Forecast soundings show convective
temperatures may be reached this afternoon, resulting some diurnal
CU. HRRR suggests by late afternoon isolated convection may be
possible over HUF and BMG. Thus a VCTS window was used at that time
given the warm and humid air mass.

Overnight, another upper wave is suggested to pass across Indiana,
with the best forcing found across southern Indiana. Forecast
soundings at most spots trend toward saturation overnight, while the
HRRR suggests convection pushing across BMG IND and HUF overnight.
Best confidence for this is at BMG which is closest to the lingering
boundary that remains from earlier convection. Thus have used a
tempo group for BMG while other locations only get a VCTS wind for
lower confidence at this time. Any TSRA that strikes a TAf site may
result in MVFR/IFR conditions.

High pressure and VFR will return on Wednesday morning as high
pressure begins to build across the region.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for INZ060>065-067>072.

&&

$$

UPDATE...BRB
SHORT TERM...AGM
LONG TERM...MK
AVIATION...Puma