Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 231916

Area Forecast Discussion
National Weather Service Indianapolis IN
316 PM EDT Tue May 23 2017

The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated below.


Issued at 314 PM EDT Tue May 23 2017

Wet weather will move back into central Indiana overnight and hang
around through the day on Thursday. By Thursday night upper ridging
starts to build into the area and conditions should be dry until
midday Friday. An upper wave will approach then along with another
frontal system and they will keep chances for showers and
thunderstorms in the forecast through Sunday.


.NEAR TERM /Tonight/...

Issued at 314 PM EDT Tue May 23 2017

An upper low will swing southeast from Minnesota tonight and bring
some upper forcing in from the west tonight. Chances for rain will
increase from west to east through the night, and eastern counties
will likely remain dry until early Wednesday morning. A broad
surface low looks like it will begin to form over the area late
during the overnight. Low temperatures should still be able to drop
into the low to mid 50s despite ample cloud cover due to cooler
temperatures aloft.


.SHORT TERM /Wednesday through Friday/...

Issued at 314 PM EDT Tue May 23 2017

Wednesday the day will start with surface low pressure centered
possibly directly over Indiana, but it will be pretty broad. The
circulation firms up and strengthens through the day but also moves
off to the southeast before it circles back over the area. This is
due to the stalling track of the upper low. The best upper forcing
will move through the area during the afternoon and thus have
categorical pops during that time. Some instability will be
available as southerly flow ahead of the low draws moisture up into
the low itself. While severe chances look better to the east, the
surface low over the area and a boundary hanging behind the low as
it moves east will allow for a very localized increase in low level
vorticity. LCLs will be low also due to the presence of the surface
low and thus will need to monitor for isolated weak tornado

The low spends Wednesday night wrapping up before moving out of the
area during the day on Thursday. This will keep rain over the area
through much of Wednesday night, and through at least the morning in
the eastern counties as it exits. The presence of the upper low will
also keep high temperatures in the 60s on both Wednesday and
Thursday as temperatures aloft are cooler in the base of the upper
low and cloud cover will be ample.

Thursday night brief upper ridging moves through the area and should
dry things out and clear out sky cover. Friday should be dry through
midday but by afternoon the upper ridging is moving to the east and
another upper wave is approaching and could bring in chances for
showers and thunderstorms in the warmer southwest flow.


.LONG TERM /Friday Night through Tuesday/...
Issued at 258 PM EDT Tue May 23 2017

Unsettled and active weather is the headline for the upcoming
holiday weekend as a frontal boundary and wave aloft combine to
bring the potential for scattered convection to impact central
Indiana at times through Sunday.

A broad upper low will set up over the Canadian prairies with
pieces of energy ejecting from the base of the parent low east
into the Mississippi and Ohio Valleys within a wavy southwest flow
aloft regime. Aforementioned frontal boundary will align across
the Ohio Valley beginning Friday night and remain over the area
before shifting southeast by late weekend as the upper low drops

While model differences in timing remain...some clarity starting
to develop in terms of timing higher impacts to the area and
potential for heavy rainfall and severe weather. An initial wave
tracking through the area and along the boundary Friday night and
early Saturday showing hints of a potential MCS. Additional
impacts appear likely Saturday afternoon and evening with
possibility for robust convection in the vicinity of the frontal
boundary to develop in a warm and modestly unstable airmass. CIPS
analogs strongly suggestive that highest severe weather threat may
exist across central Indiana on Saturday.

Convective threats diminish through the day Sunday as the front
shifts south and region comes under the influence of cyclonic flow
associated with the upper low sagging into the Great Lakes. At
this point...dry and cooler weather is expected for early next
week although a lingering presence of northwest flow aloft as the
week progresses is suggestive of a continued convective threat.


.AVIATION /Discussion for 231800z TAF issuance/...

Issued at 1257 PM EDT Tue May 23 2017

VFR through the rest of the day with light southeasterly winds.
KLAF will have light showers nearby but they are widely scattered
and unlikely to impact flight category so just included a VCSH.
Ceilings will develop overnight as low pressure system gets closer
and brings initially scattered showers and then more widespread
rain to the sites. MAV/MET showing IFR/low IFR ceilings developing
at the sites mid morning Wednesday for at least a brief period,
but SREFS show only low probabilities of even MVFR. Thus for now
will go with MVFR ceilings overspreading the area after around
9-12z and leave IFR out for this issuance. Winds should be light
and pretty variable with surface low meandering across the area




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