Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 210506
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
105 AM EDT Fri Jul 21 2017

.UPDATE...

The Aviation section has been updated below.

&&

.SYNOPSIS...
Issued at 335 PM EDT Thu Jul 20 2017

A strong upper ridge over the southern and central plains and
lower Mississippi valley will produce very hot and humid conditions
through Saturday.  A frontal system over the southern great lakes
will move to the northern part of our forecast area later tonight...
then stall and move back to the north later Friday.

Another cold front will move our way by Sunday as an upper trough
digs into the great lakes.   The long term period will be not as
hot.   High pressure will dominate our weather Monday through
Wednesday.   Then another system will move our way by Thursday.

&&

.NEAR TERM /Tonight/...
Issued at 910 PM EDT Thu Jul 20 2017

Mid level vorticity center currently moving into northwest
Indiana. Some convection has been trying to develop near this
feature over the past couple of hours, but cap seems to be holding
so far. This feature is expected to drop southeast into west
central Ohio during the pre dawn hours of Friday, while a trailing
vorticity lobe hangs back across the area. Short term model data
suggest winds in the 925-850mb layer may increase some over the
next 2-3 hours, so may start to see more robust development by
then.

Forecast still looks good at this time, with PoPs tonight centered
over the northeast two thirds of the forecast area, fairly well
aligned with where the trailing vorticity lobe will be. No updates
planned at this time.

Previous discussion follows.

The thunderstorm complex which brought storms midday has moved on
to the east.  Rather quiet weather will be the rule next few hours.
This will be followed by increasing chance of storms across our
northern sections by late evening as a cold front over the
southern great lakes moves our way.  Models indicate good low
level convergence near this front and thunderstorms should develop
this evening over the middle and upper Mississippi valley and move
our way overnight.

SPC has the northern half of our forecast area in a slight risk of
severe weather overnight.   Locally heavy rain is also possible
as precipitable water is over two inches.   Will go with high chance
POPS towards midnight across our north...while southern sections
remain dry.

Lows tonight will be in the lower to middle 70s which is close to a
MOS blend.

&&

.SHORT TERM /Friday through Sunday/...
Issued at 335 PM EDT Thu Jul 20 2017

The front across our north will move back to the southern great
lakes by Friday night....while a strong upper ridge remains across
the lower Mississippi valley and southern plains.   The main issues
next few days will be how hot and humid it gets and also
thunderstorm chances.

850 MB temperatures will be a little warmer next few days with lower
20s across our south.  This translates to highs in the lower to
middle 90s and this combined with dewpoints in the middle to upper
70s will produce index values from 105 to 108 degrees across parts
of our south.  Will add a few more counties to the heat advisory to
the heat advisory beginning tomorrow.  This includes Greene and
lawrence counties through Jennings counties across our south.  All
heat advisories will then remain in effect until 23Z Saturday.

In regards to POPS...there should be a lull tomorrow morning
followed by chance POPS most areas Friday afternoon.  With the front
farther north...southern sections should be mostly dry Friday night
and Saturday...while a chance of storms will be the rule in the
north.     Raised POPS a little most areas Saturday night as the
cold front again moves our way.

Sunday will be a tad cooler with a few storms south.

&&

.LONG TERM /Sunday night through Thursday/...
Issued at 213 PM EDT Thu Jul 20 2017

The long term begins with Indiana having an upper wave move through
along with a front moving to the south. Thus will keep the slight to
low chance pops from the Superblend, and these will move off to the
southeast late Sunday night and Monday. Cooler highs (low to mid
80s) will be in place for Monday and Tuesday, but upper ridging
begins building back in and temperatures will start warming trend on
Wednesday. Medium confidence of dry weather Tuesday through
Wednesday under building upper ridge. The next system then
approaches on Thursday as the upper ridge suppresses and more
chances for storms arrive. Looking at thicknesses and upper pattern
though would not be surprised if high temperatures wind up a little
warmer than going forecast.

&&

.AVIATION /Discussion for the 21/06Z TAFs/...
Issued at 105 AM EDT Fri Jul 21 2017

Scattered convection possible mainly in the vicinity of the
KLAF/KIND terminals overnight in association with a strung out
vorticity lobe from west central Ohio back into northern Illinois,
coupled with some enhanced flow in the 925-850mb level. Brief
IFR visibility restrictions and gusty shifting winds in and near
the heavier cells. CB bases around 035.

Otherwise, areas of mainly MVFR visibility restrictions in light
fog expected through about 211200Z, given the light winds and high
dewpoints. Due to some cloud cover and potential convective
outflows, will keep restrictions above IFR for now.

Light surface winds overnight expected to become 220-250 degrees at
8-10 kts by midday Friday.

&&

.IND WATCHES/WARNINGS/ADVISORIES...

Heat Advisory from noon Friday to 7 PM EDT Saturday for INZ061-
070>072.

Heat Advisory until 7 PM EDT Saturday for INZ060-067>069.

&&

$$

SYNOPSIS...JH
NEAR TERM...JH/JAS
SHORT TERM...JH
LONG TERM...CP
AVIATION...JAS


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