Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 270428
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1227 AM EDT SAT AUG 27 2016

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

&&

.SYNOPSIS...
Issued at 253 PM EDT Fri Aug 26 2016

A front will meander across the area during the weekend keeping
chances for showers and thunderstorms in the forecast. Another
frontal system will bring more rain chances then through mid week.
Temperatures will remain above normal through early next week, then
return to closer to average.

&&

.NEAR TERM /Overnight/...
Issued at 1030 PM EDT Fri Aug 26 2016

Rain largely out of the forecast are as of this writing at 0230Z.
Muggy airmass remains with temps currently in the low to mid 70s.

Where to start. Beginning to sound like a broken record as Mother
Nature took it out on central Indiana yet again tonight. This
time...flash flooding was the impact and primarily focused on the
Indy metro at the tail end of rush hour. The combination of a
remnant front in the area and a plethora of outflow boundaries
interacted with the very moist and unstable airmass to generate
strong slow moving convection. 2 to 3.5 inches was common over
about 60-75 mins in a swath from near Mooresville northeast
through the city up to near Fishers. While the rain has
ended...lingering flooding persists in pockets across the metro
with water receding in creeks...streams and roadways. Have
continued an areal flood warning through midnight to cover.

Airmass has been worked over pretty well but considering the
leftover boundaries and presence of a rich plume of moisture
highlighted by precip water values in excess of 2 inches...really
cannot rule out an thunderstorm at any point overnight. Only
exception to this is across far eastern/southeastern counties as
drier air underneath the ridge aloft pokes into the area. Upper
wave generating convection over the western Tennessee and lower
Ohio Valleys currently will rotate around the flank of the ridge
overnight and may produce an uptick in convective coverage over
western counties during the predawn hours. Will carry highest pops
here. Should these storms work up into the area...heavy rain and
localized flooding would be the primary impacts.

Zone and grid updates out.

&&

.SHORT TERM.../Saturday through Monday/
Issued at 253 PM EDT Fri Aug 26 2016

Focus remains on chances for rain through the period. Models are
pretty close overall with the big picture but differ on when/where
better chances for rainfall will occur. Thus not a lot of confidence
in pops through the period with no clear focus for forcing of
convection through most of the period.

The old frontal boundary will remain in the area into the weekend.
Area will generally remain on the periphery of an upper high, which
will allow various upper disturbances to rotate around the high into
the area. Since timing of these features is uncertain, uncertainty
in timing of pops is higher.

Higher pops will exist on Saturday as our area will also have some
additional upper support from the right rear entrance region to an
upper jet to our north. Thus will go higher end chance category pops
Saturday into Saturday evening.

Otherwise with no clear focus for convection generally went slight
chance pops at night and low chance pops during the day through
Monday.

Hot and humid conditions will persist through the short term with no
significant change in airmass expected. A model blend of
temperatures reflects this well.

&&

.LONG TERM /Monday Night through Friday/...
Issued at 236 PM EDT Fri Aug 26 2016

Models suggest the area will be on the periphery of weak upper level
ridging, particularly early in the week. Thunderstorm chances will
be necessary much of the long term, but cannot justify more than 20
to 30 pops as convection will be either diurnally driven or subject
to subtle disturbances that models simply cannot handle on such time
scales.

Blended initialization was reasonable and required only minor
changes.

&&

.AVIATION /Discussion for the 270600Z TAFS/...
Issued at 1227 AM EDT Sat Aug 27 2016

Can`t rule out widely scattered convection overnight given the weak
frontal zone in the area, but 850mb flow looks fairly weak tonight,
so don`t think the convective threat is all that high overnight.

Model guidance suggests remnant vorticity center from convection over
the Tennessee Valley will be drifting north into the local area
by the mid morning hours of Saturday. As a result, convective threat
should increase across the terminals by that time.

Some concern for the development of IFR ceilings/visibilities
overnight given the nearly saturated air mass, but with expected
higher level cloud cover, confidence in IFR is low.

Light surface winds overnight expected to become 120-160 degrees at
5-8 kts by late morning Saturday.

&&

.IND Watches/Warnings/Advisories...
NONE.
&&

$$

SYNOPSIS...50
NEAR TERM...RYAN
SHORT TERM...50
LONG TERM...NIELD
AVIATION...JAS/JP



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