Special Weather Statement, NWS Indianapolis, IN

Area Forecast Discussion
National Weather Service Indianapolis IN
231 PM EDT Tue Aug 1 2017

.UPDATE...
The LONG TERM Section has been updated below.

&&

.SYNOPSIS...
Issued at 238 AM EDT Tue Aug 1 2017

Scattered thunderstorms will develop in warm and increasingly humid
air across central Indiana today and Wednesday. A cold front will
bring better chances for thunderstorms Thursday and Thursday night.
An upper level system could bring more rain chances for the second
half of the weekend into early next week. Near normal temperatures
will give way to below normal readings late this week into early
next week.

&&

.NEAR TERM.../Rest of Today/
Issued at 1010 AM EDT Tue Aug 1 2017

Going forecast appears on track for development of isolated to
widely scattered showers and thunderstorms this afternoon. Previous
discussion follows...

An upper trough will settle in across the area today. Water vapor
satellite shows a vort max moving into northern Illinois early this
morning. Weak high pressure will be in the vicinity at the surface.

With the upper trough across the area today, feel there will be some
thunderstorm development when instability increases this afternoon.
The vort max moving in from Illinois may increase coverage across
northern sections of the area. However, the weak high pressure will
be working to lower the coverage of convection.

With the high in the area, feel that the model blend is overdoing
coverage of storms. Will go with slight chance PoPs across the
southwest 2/3 of the area, with chance PoPs across the northeast
1/3 (where the vort max might produce additional forcing).

For temperatures, went above the model blend based on recent
performance and the fact that the blend is overdoing coverage of
rain.

Confidence is high that there will be some thunderstorm development
but medium in terms of coverage.

&&

.SHORT TERM.../Tonight through Thursday night/
Issued at 238 AM EDT Tue Aug 1 2017

Models are close enough that the model blend initialization
was accepted for most items.

The broad upper trough will remain across the area through
Wednesday. With no decent forcing expected, feel convection will
continue with a mainly diurnal influence. This means diminishing
during the evening and peaking in the afternoon. Will keep PoPs in
chance category or lower.

On Thursday a stronger upper trough and a surface cold front will
approach the area. Will go chance PoPs as the main forcing remains
west of the area during the day.

Forcing looks good enough for likely PoPs Thursday night as the cold
front and upper trough move in along with an upper jet.

The model blend looks good for temperatures given expected
conditions.

Confidence is medium during the short term as timing of the best
chances for rain could still shift some.

&&

.LONG TERM /Friday Night through Tuesday/...
Issued at 231 PM EDT Tue Aug 1 2017

Cool and dry weather initially in the wake of the frontal passage
for the weekend under the influence of a broad upper trough will
transition back to an active and unsettled pattern.

An unusually strong upper low for this time of year will dive into
the Great Lakes by Friday night...serving to amplify and
strengthen the upper trough over much of the eastern part of the
country. With high pressure at the surface...dry weather with
pleasant temperatures will continue Saturday as highs remain in
the 70s. The high will drift off to the east Sunday with return
flow developing ahead of a sharp upper wave poised to drop into
the region for Sunday night and Monday. A frontal boundary will
accompany this feature with chances for showers and storms
increasing through the period as a result.

Current trends in the long term guidance suggestive of the
frontal boundary moving far enough south of central Indiana to
allow for largely dry weather for Tuesday before the frontal
boundary returns north into the Ohio Valley just beyond the 7 day
for midweek...with potential fro rain and thunderstorms resuming.
Highs in the upper 70s and lower 80s will be common through early
next week. The hot weather that often is a staple during the first
half of August are nowhere to be found on the horizon at this
time either as trends support continued influence of troughing
aloft east of the Mississippi River through late next week.

&&

.AVIATION /Discussion for 011800z TAF issuance/...

Issued at 114 PM EDT Tue Aug 1 2017

Scattered convection is developing cross central Illinois and
northern Indiana, but much of central Indiana remains storm free
as of 1 pm EDT. Based on more stability from high pressure to the
south and east, will leave any thunder mention out of KIND and
KBMG as coverage, if any, near those locations should be isolated
at worst this afternoon and early evening. Some storms are within
20 miles of KHUF at this time, so will include a VCTS there
starting in around an hour or so, and will follow a similar plan
for KLAF. This convection is diurnal and should dissipate this
evening so will drop any mention around 23-1z. If any of the sites
do get rain, they have a better chance at developing overnight
fog. At this time KLAF appears to have the highest chances for
fog based on guidance and soundings, but KHUF and KBMG could have
chances as well, mainly between 9 and 13z.

Tomorrow afternoon looking at more chances for scattered showers
and thunderstorms, but too low confidence in location and timing
to include in the extended portion of the KIND TAF.

&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE.

&&

SYNOPSIS...50
NEAR TERM...50/CP
SHORT TERM...50
LONG TERM....Ryan
AVIATION...CP

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