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Forecast Discussion for Indianapolis, IN

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000
FXUS63 KIND 172309
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
709 PM EDT Sat Aug 17 2019

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 315 PM EDT Sat Aug 17 2019

Warm and humid airmass returns to the Ohio Valley, with a frontal
boundary nearly stationary over the region through the next
several days. Occasional chances for showers and thunderstorms
will persist, until possibly late in the week when some cooler air
will try to push into Central Indiana.

&&

.NEAR TERM /Tonight/...
Issued at 315 PM EDT Sat Aug 17 2019

Main concern for this evening and the overnight will revolve
around chances for redevelopment of thunderstorms. The afternoon
convection that worked east/southeast across Central Indiana has
pushed a boundary further south along the Ohio River, and return
flow moisture and instability has been slow to recover. Visible
satellite imagery indicates some clearing or at least erosion to
the thicker cloud shield brought by the precip shield, but not
much new cumulus clouds in it`s wake at this point in the
afternoon. Further upstream the atmosphere still looks rather
stable as well, and expect several hours of dry conditions through
much of this evening.

Closer to midnight and the early Sunday morning hours guidance
begins to differ on placement of the next vort speed max. Some of
the hi-res guidance members have been trending further northwest
with the vort-max, suggesting the focus for redevelopment will
track further northwest of Central Indiana overnight and could
translate into a quieter overnight than earlier anticipated. The
wildcard will be on warm-air advection from the boundary lifting
north and the very moist low-level environment providing a primed
environment with rising parcels helping to kick-off a few
scattered showers/embedded thunderstorms overnight. This, no pun
intended, appears to hold more water in how the overnight will
unfold. So have maintained a chance for showers and storms,
focused along and north of interstate 70. Temps will remain mild
with lows only falling into the lower 70s. With lighter winds, and
recent rainfall along with a minimal T/Td spread, expect some
patchy fog to also develop.

&&

.SHORT TERM /Sunday through Tuesday/...
Issued at 315 PM EDT Sat Aug 17 2019

Broad upstream trough will maintain a southwest flow for much of
the Missouri/Ohio Valleys through at least mid-week. The sensible
portion of the atmosphere will feature a quasi-stationary frontal
boundary meandering north/south across Central Indiana the next
several days, with periodic chances for showers and storms. For
Sunday guidance has been hinting at a weakening vort-max pushing
east over the region, but also possibly trending further north in
the path. This would suggest the stronger storms and would
follow the greater instability axis, with just some less potent
convection further south/southeast across Central Indiana.
However, some earlier solutions were indicating a diving southeast
path to the stronger vorticity, which would likely bring stronger
storms southeast towards Central Indiana Sun midday/afternoon. The
key will be how convection develops later this evening/overnight
across Iowa/Kansas, as the steering would indicate that area of
convection would slide east/southeast towards the forecast area.

Sunday night through Tuesday will be near carbon copies of
each other, with minimal shear throughout the lowest 6km of the
atmosphere. Given the increased PWAT in the atmosphere, and recent
rainfall, the heat capacity of the surface will likely help to
hold temps in the upper 80s to perhaps lower 90s. But the downside
will be the apparent temps pushing into the upper 90s to a few low
100s during peak heating Mon/Tue afternoons.

&&

.LONG TERM /Tuesday night through Saturday/...
Issued at 234 PM EDT Sat Aug 17 2019

Models in similar agreement that a cold front will drop southeast
across central Indiana Tuesday night into Wednesday. The front and
upper waves in northwest flow will interact with a hot, humid and
unstable airmass and result in at least scattered convection Tuesday
night and Wednesday. The thunderstorm chances will be ending
Wednesday night into Thursday northwest to southeast as the front
departs.

Then, should see seasonably or below temperatures and markedly less
humidity by Thursday as Canadian high pressure builds in, per the
blend.

&&

.AVIATION /Discussion for 180000Z TAF Issuance/...
Issued at 709 PM EDT Sat Aug 17 2019

VFR conditions are expected throughout the forecast period.

Mid and high level cloud debris lingered across the area in the
wake of the convection earlier today but also starting to see some
more extensive clearing as well. An upper wave remained to the
west over the mid Mississippi Valley and is poised to lift across
the region through the evening. To this point...convection has not
fired in tandem with the wave and not sure it will considering the
airmass has really been unable to sufficiently destabilize once
again. Cannot entirely rule out isolated convective development
through 06Z as the wave passes but confidence too low for a
VCSH/VCTS mention at the terminals at this time.

Think the best risk for convective impacts at the terminals
remains on Sunday afternoon as weak disturbances aloft interact
with an increasingly moist and unstable airmass over the region.
With the frontal boundary settling over the lower Great
Lakes...convection is likely to be more focused over northern
Indiana with isolated activity further south. Too early to
consider a VC mention at this point for Sunday afternoon but
something to monitor going forward.

Light southerly flow tonight will veer to southwest on Sunday and
become breezy with potential for gusts near 20kts in the
afternoon.

&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SYNOPSIS...Beach
NEAR TERM...Beach
SHORT TERM...Beach
LONG TERM....MK
AVIATION...Ryan

Previous Forecast Discussions may be found at
NWS Indianapolis, IN (IND) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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