Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 221049
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
649 AM EDT Sat Jul 22 2017

.UPDATE...

The Aviation section has been updated below.

&&

.SYNOPSIS...
Issued at 338 AM EDT Sat Jul 22 2017

Central Indiana will remain on the edge of a strong upper ridge
through tonight....maintaining hot and exceptionally humid
conditions. Chances for thunderstorms will continue until a frontal
boundary can push through the area overnight into early Sunday. A
secondary front may bring additional scattered storms on Sunday
evening before high pressure builds in with mainly dry weather and
seasonable temperatures for the early part of the week.

&&

.NEAR TERM /Today/...
Issued at 338 AM EDT Sat Jul 22 2017

Active early morning continues across northern portions of central
Indiana as a bowing convective line moves into the northern Wabash
Valley. Yet another steamy overnight across the region as 07Z
temperatures were largely in the mid and upper 70s.

Convection and heat remain the primary concerns for today once again
as the region resides on the periphery of the heat ridge.  The first
order of business will focus on the potential for severe convection
prior to daybreak with expectations of additional robust storm
development by late day over northern counties near the sagging
frontal boundary.

Bowing feature progressing southeast across northern portions of the
forecast area at 0630-07Z. LAPS sounding at KLAF indicates the
presence of an inversion below 850mb which may be inhibiting the
strong winds being sampled via KIND radar from being fully realized
at the surface. The convection should continue tracking southeast
along the instability axis and theta-e ridge which extends through
Indy and toward the Cincy metro. Damaging wind gusts remain the
primary threat with these storms early this morning...along with
torrential rainfall and despite the quick movement to the
storms...localized flooding as well. Severe Thunderstorm Watch #431
remains in effect through 11Z for the northeast half of central
Indiana to account for the current storms.

Expect the convection will be moving on into western Ohio near
daybreak in a weakening state. The southern flank of the convection
back across northern Illinois may move across the same areas later
this morning before diminishing and will need to monitor. The
general trend though as we go through the morning and into the early
afternoon will be towards brightening skies...clouds scattering and
the focus shifting back to the heat and humidity.

With moisture pooling and a surge of heating ahead of the
approaching frontal boundary...potential is there for dewpoints to
hang in the mid and upper 70s into the afternoon as temps surge into
the 90s.  This will promote a strongly unstable airmass by late
afternoon with MLCAPEs nearing 4000 J/KG being realized immediately
ahead of the front over northern counties. With a low level jet
likely to energize over the region by late day and a remnant outflow
boundary from the morning convection setting up over northern
portions of the forecast area...expect convection to erupt quickly
after 21Z and grow upscale rapidly into the evening aided by cooling
aloft. Damaging winds will be the primary severe weather threat but
all forms of severe weather will be possible.  Precip water values
above 2 inches will support a continuing heavy rain and flooding
threat as well.

Temps...as mentioned above...heat and humidity will again be factors
today. Expect highs ranging from the upper 80s over northeast
counties where convective impacts lend towards more uncertainty on
temps to mid 90s in the lower Wabash Valley.  Max heat indices again
will get above 100 degrees in most areas with the highest values
over southwest counties.  The heat advisory will continue in
its current state and location until 23Z.

&&

.SHORT TERM /Tonight through Monday Night/...
Issued at 338 AM EDT Sat Jul 22 2017

Forecast challenges focus on precip chances...especially tonight and
again late Sunday and Sunday evening.

Convection will likely be ongoing this evening as development takes
place over northern counties and progresses southeast through the
evening and overnight ahead of the cold front.  A surface wave along
the boundary...continued influence of a low level jet...BL shear
values around 30kts and a strongly unstable airmass all support a
threat for severe storms this evening gradually transitioning into
more of a heavy rain threat overnight. Highest pops will be employed
over the eastern half of the area where parameters will be just a
bit more favorable for more widespread convection. Precip water
values will remain above 2 inches and combined with freezing levels
near 15kft supporting warm rain processes...torrential rainfall and
flooding will continue to be concerns as the storms surge south
overnight.

Growing confidence that most if not all of the convection will be
out of the forecast area by 12Z Sunday with the front settling south
of the Ohio River.  Much of the day Sunday should be dry with an
edge being taken off the humidity levels. A secondary front
associated with a sharp upper wave diving out of the western Great
Lakes may serve as a focal point for renewed convective development
to the northwest of the region Sunday afternoon...possibly spreading
into the northern half of the forecast area during the evening.
Steep mid level lapse rates in response to cooling aloft suggestive
that strongest storms may carry a damaging wind and large hail
threat.  Will bring low chance pops back into the northern counties
Sunday evening as a result.

Convection will diminish overnight Sunday with high pressure
building south into the region on Monday with cooler and noticeably
less humid air. Likely to see diurnal cu develop on Monday before
skies become mostly clear Monday night.

Temps...it will remain very warm on Sunday with low level thermals
supporting highs from the mid 80s to around 90. Temps will fall back
into the lower and middle 80s Monday with cooler air aloft advecting
into the region. Lows will slide back into the 60s through the
period.

&&

.LONG TERM /Tuesday through Friday/...
Issued at 338 AM EDT Sat Jul 22 2017

High pressure will maintain the dry and pleasant airmass across
central Indiana and the Ohio Valley through midweek before a more
active pattern returns as a cold front drops through the area late
week.

The upper ridge that will be squashed back to the southwest by
Monday will begin a reexpansion back towards the area by the middle
of next week with southerly flow reestablishing.  This will lead to
a progressively warm and more humid airmass back into the forecast
area by Wednesday as highs rise into the upper 80s to near 90 over
much of the region. A cold front will track slowly south into the
area by Thursday...forcing the core of the ridge to retrograde back
into the southern Plains as mid level heights buckle once again.

The best chance for convective impacts over central Indiana will
exist on Thursday and Thursday night as the frontal boundary is
draped across the Ohio Valley.  The boundary should shift south of
the region by Friday with rain chances diminishing as weak high
pressure expands in from the north.

&&

.AVIATION /Discussion for the 22/12Z TAFs/...
Issued at 646 AM EDT Sat Jul 22 2017

Predominantly VFR through the period outside of convection.

Convection will be a threat early in the period at LAF and later
this afternoon into the evening at the other sites. Uncertainty
precludes more than a VCTS mention at this time.

Winds throughout the period will be 10KT or less, predominantly
out of the southwest, becoming west and northwesterly late in the
period.

&&

.IND WATCHES/WARNINGS/ADVISORIES...

Heat Advisory until 7 PM EDT this evening for INZ051>053-060>062-
067>072.

&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM...Ryan
AVIATION...NIELD



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