Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 211413
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1015 AM EDT Fri Jul 21 2017

.UPDATE...
Near Term and Aviation sections have been updated below.

&&

.SYNOPSIS...
Issued at 352 AM EDT Fri Jul 21 2017

Central Indiana will remain on the edge of a strong upper ridge into
Saturday.  This will maintain hot and exceptionally humid
conditions...along with threat for clusters of thunderstorms to
impact the region.  A frontal boundary will shift south of the area
by early Sunday with drier and slightly cooler air spreading into
the region for the second half of the weekend. High pressure will
bring mainly dry weather with seasonable temperatures beginning
early next week.

&&

.NEAR TERM /Rest of Today/...
Issued at 1015 AM EDT Fri Jul 21 2017

Area of thunderstorms which affected the northeast half of our
forecast area was moving out to the east.  Storms over northeast
Illinois were dying out while storms over northwest Illinois
remained.  Mostly quiet weather will occur next several hours
with thunderstorms increasing again after 200 or 300 PM.

Rapid refresh is a little quicker and more bullish with
thunderstorms later today as opposed to yesterday.   Will carry 20%
POPS all but southwest through early afternoon and then higher
chance POPS most areas after that.  Models are a little quicker in
developing thunderstorms over southern sections today.  This may
inhibit temperatures a little across our southeast.  Will leave
headlines and temperatures as is for now as it will not take too
long of a break for them to rise to near heat advisory criteria.

Portion of previous near term discussion follows...Temps...the other
big issue today is the heat and humidity. Kept highs nearer to the
cooler MAVMOS considering potential impacts to part of the forecast
area from debris clouds and convection. With that being said...even
a few hours with sunshine will enable temps to rocket similar to
Thursday afternoon in the wake of the storms over the northern half
of the forecast area. Will carry a range on highs of upper 80s over
the northeast to near 95 in the lower Wabash Valley. Dewpoints will
likely hold in the mid to upper 70s for large chunks of the day and
any rainfall will just enable dewpoints to rise even higher.  Max
heat indices will make it to 100 in most areas with 105 or better
across the southwest.  Will be adding in four more counties to the
heat advisory for today where max heat indices should reach 105 or
better...Vigo...Clay...Owen and Monroe Cos.

&&

.SHORT TERM /Tonight through Sunday Night/...
Issued at 352 AM EDT Fri Jul 21 2017

Forecast challenges focus on precip chances through Sunday before a
cold front shifts the heat...excessive humidity and storms all to
the south by the end of the weekend.

Convection will likely be ongoing along the remnant boundary this
evening before diminishing in coverage after dark. Large
thunderstorm cluster expected to develop over the Upper Midwest
ahead of a surface low late today into this evening...then turn
southeast into the Great Lakes along the upper ridge periphery
tonight.  Will have to monitor the evolution of this system as parts
of this complex could spread back into the forecast area overnight.
Storms would once again carry a severe weather and flooding threat
with them.

Capping will likely reestablish on Saturday with any convection
likely to remain isolated at best until peak heating during the
afternoon when more robust development can take place along any
leftover boundaries.  The approach of the frontal boundary from the
north by late day along with cooling aloft should amplify the
convective threat for the late afternoon and evening with storms
becoming more numerous as a low level jet develops as well. These
storms Saturday afternoon and evening will again carry a potential
for severe weather with damaging winds as the primary threat. While
the storms should be moving...torrential rain and flooding will be
concerns with precip water values being progged in excess of 2.25
inches with a freezing level at 15-16kft supporting warm rain
processes.

Most rain and storms will shift south of the forecast area Sunday as
the front settles into the Tennessee Valley.  Weak high pressure
will build in and bring a drier end to the weekend along with
slightly cooler and less humid air through Sunday night.

Temps...one last hot and humid day for Saturday as most areas should
warm into the lower and possibly mid 90s. Heat indices will again
rise into the low 100s. Low level thermals support highs mainly in
the mid and upper 80s for Sunday with dewpoints slipping back to a
slightly more comfortable level in the upper 60s to near 70.

&&

.LONG TERM /Monday through Friday/...
Issued at 204 AM EDT Fri Jul 21 2017

The long term portion of the forecast will present an opportunity
for temperatures to cool down nearer to seasonal normals and at
least a window of dry weather.

A remnant boundary near the Ohio River may produce a few showers
and storms on Monday, but from Monday night through early
Thursday, surface high pressure moving through the area will keep
conditions dry and far more comfortable, with dewpoints likely to
be in the low to mid 60s rather than the current unpleasant low to
mid 70s.

Late in the week, northwest flow reestablishes and a frontal
system appears likely to begin to influence the area. This will
necessitate a return to daily chances for thunderstorms.

Blended initialization handled things relatively well and few
major changes were required.

&&

.AVIATION /Discussion for the 21/15Z KIND TAF Update/...
Issued at 1015 AM EDT Fri Jul 21 2017

Minor tweaks made to KIND TAF to better match current conditions.
No other changes are needed at this time.  Portion of Previous
aviation discussion follows...

Predominantly VFR through the period.

Will carry VCTS again later this afternoon at all sites as an
upstream MCV will move into the area and may spark more widespread
activity yet again.

Cannot rule out drops into MVFR and perhaps brief IFR with the
more intense thunderstorms, but again, uncertainty precludes
mentioning this.

Winds through the period will be less than 10KT, occasionally
variable.

&&

.IND WATCHES/WARNINGS/ADVISORIES...

Heat Advisory from noon today to 7 PM EDT Saturday for
INZ051>053-061-062-070>072.

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

&&

$$

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



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