Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 260749
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
349 AM EDT Fri May 26 2017

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated
below.

&&

.SYNOPSIS...
Issued at 349 AM EDT Fri May 26 2017

Active weather is expected through the holiday weekend as a frontal
boundary oscillates over the region and interacts with upper level
waves moving through the Ohio Valley. Expect multiple opportunities
for strong to severe storms with heavy rainfall until a cold front
sweeps through the area late Sunday. With the exception of a
secondary front bringing low chances for storms Tuesday...expect
primarily dry weather for much of next week with seasonable
temperatures.

&&

.NEAR TERM /Today/...
Issued at 349 AM EDT Fri May 26 2017

Mainly clear skies across central Indiana early this morning with a
surface ridge over the region. With light wind flow and plenty of
lingering near surface moisture...already seeing fog develop across
the forecast area and expect this to continue through daybreak. 07Z
temps were in the 50s across the area.

The respite in the active weather will be brief as the combination
of a frontal boundary setting up over the region and pieces of
energy aloft kick out of the base of a deep upper trough centered
over the northern Plains. The initial impacts of this developing
pattern will likely arrive over parts of the area by late day.

The primary issue for this morning is the fog which should continue
to expand in coverage through the predawn. Not expecting fog to
become widespread or particularly dense...but it will impact morning
travel in spots through daybreak before improving. Much of the day
will be dry as ridging at the surface and aloft remains over the
Ohio Valley into early afternoon.

The potential troublemaker for later today and into tonight is an
upper wave tracking through the central PLains early this morning
with a convective complex in tandem moving east across Kansas. The
upper wave is progged to track E/NE into the lower Great Lakes by
late afternoon...gradually flattening the ridge aloft as it moves
into the area tonight. Model guidance is all over the place with the
handling of the wave and more specifically the convective complex.
Already noticing that some of the model data is too far north with
current convection in eastern Kansas. Furthermore...most of the
model guidance including the hi-res solutions supporting a weakening
trend to the storms through 12Z. Considering the presence of the
nocturnal jet through daybreak...disagree with the model consensus
and expect these storms to maintain their intensity for the next
several hours. The only solution this morning that appears to have
somewhat of a handle on current activity is the HRRR which weakens
the complex slightly...then fires it up again over southern Iowa and
northern Missouri by midday.

This complex should ride the developing warm front through the
afternoon and is likely to be approaching northwest portions of the
forecast area by late afternoon...spreading southeast into the
region into the evening. The HRRR remains the preferred solution
with subtle support from the WRF guidance as well. With deeper
moisture...increasing instability and ample shear and storm relative
helicity present...a severe threat will exist with these storms as
they approach the region late this afternoon. More will be discussed
on these storms in the short term section as they are likely to
impact the forecast area this evening and tonight.

Temps...an overall model blend looked quite reasonable for highs
across the region today.  Expect mid 70s to low 80s from northeast
to southwest.

&&

.SHORT TERM /Tonight through Sunday Night/...
Issued at 349 AM EDT Fri May 26 2017

Forecast challenges primarily focus on convective threats as the
frontal boundary in the region interacts with waves aloft through
much of the short term. Confidence is lower than desired in this
pattern as mesoscale factors will impact heavily on timing and
location of convection.  With that being said...potential is high
for multiple convective complexes to impact central Indiana and the
Ohio Valley with heavy rainfall and all modes of severe weather.
Needless to say...the bulk of the holiday weekend is shaping up to
be a busy one.

First issue will be the convective complex likely to be ongoing from
late this afternoon.  The global models appear to be too far north
with the track of the convective complex and as mentioned in the
near term section...have leaned much closer to the hi-res model
suite for a starting point with the storm complex late today into
tonight. As mentioned...the arrival of the upper wave will flatten
the ridge aloft over the area and consequently should enable the
complex to turn E/SE over the region this evening as it tracks
towards the deeper moisture and instability. The question to still
be resolved is how far south convection will impact across central
Indiana as model soundings and mid level temperatures both highlight
a capping inversion present further southwest over the forecast area
back into the lower Ohio Valley. Confidence is highest in impacts
over the northeast half of the forecast area and will carry highest
pops in these areas through the evening with lower pops further
southwest where higher uncertainty exists regarding the influence of
the cap. Severe potential will continue with these storms through
the evening into the early overnight along with heavy rain and
localized flooding. May eventually need a flash flood watch for
tonight but would like to see how the convection evolves
through the day before committing to a headline.

The convective complex should largely be east of the area by predawn
Saturday with subtle ridging aloft reestablishing over the area by
midday Saturday. The track of the complex tonight will likely play a
large part in determining how far south the front sags and
eventually sets up for the second round of significant convection
for late Saturday and Saturday night. Model consensus favoring the
boundary setting up near the Ohio River by Saturday afternoon before
returning north Saturday night as a surface wave tracks along the
boundary. Near and south of the front...impressive instability and
moisture will be available with a capped airmass further north. Yet
another strong wave aloft kicking out of the deep upper low to the
northwest and the aforementioned surface wave will be the features
that help initiate rapid and robust convective development Saturday
afternoon over the Missouri Valley before moving east into the Ohio
Valley. Expect this will likely result in most of the forecast area
remaining dry much of the day Saturday.

The convection to the west should develop upscale into yet another
convective complex poised to track into the area Saturday evening
and night ahead of the surface wave. At this time...the greatest
threat for severe storms and primary impact from the complex is
expected along and south of I-70 in closer proximity to the expected
location of the boundary. The presence of the front alone would
support a tornado threat...but the combination of strong instability
with CAPEs in excess of 3000 j/kg and wet bulb zero values around
10kft suggest damaging winds and large hail are likely to be the
bigger threats. Storms should once again diminish predawn Sunday
into Sunday morning as the surface wave shifts east.

Should see another break in the wet weather for the first half of
Sunday before scattered convection increases again during the
afternoon ahead of a cold front and the parent upper trough. The
airmass will become increasingly unstable in the humid airmass ahead
of the cold front with the potential for a third round of severe
storms set to impact the forecast area as BL shear values increase
above 40kts. The cold front will sweep east of the forecast area
Sunday evening with rain and storms ending from the west.

Temps...held close to a model blend for highs and lows through the
short term as they will be easily influenced by the timing and
location of convective complexes. Overall...expecting highs from the
mid 70s to lower 80s both Saturday and Sunday and lows primarily in
the 60s tonight and Saturday night followed by cooler weather behind
the front Sunday night.

&&

.LONG TERM /Sunday Night Through Thursday/...
Issued at 219 PM EDT Thu May 25 2017

Ensembles in fairly good agreement on the main weather features
during this period. Upper troughing is expected to drift east
through the Great Lakes through the early parts of next week, with
the flow flattening out towards the middle of the week.

Ensembles suggest an upper disturbance rippling through the Great
Lakes trough may move through the area either Monday or Tuesday of
next week, with the majority leaning towards Tuesday. Will keep
some chance PoPs going for Monday and Tuesday to cover this feature.

Some of the ensembles are quite aggressive in ejecting an upper low
of the southwestern deserts into the local area later next week.
Would like to see more continuity with this feature. For now, will
keep next Wednesday and Thursday mainly dry and monitor trends.

&&

.AVIATION (Discussion for the 260600Z TAF Issuance)...
Issued at 1137 PM EDT Thu May 25 2017

MVFR visibilities expected to develop overnight, then quickly return
to VFR by 13Z. MVFR ceilings may develop after 00Z, especially west.

Dissipating lower clouds and lightening winds should allow for some
MVFR fog to develop overnight. This will burn off quickly with VFR
returning by 13Z. Some cumulus and mid/high clouds will then rule
the daylight hours, with perhaps some lower clouds moving back in
after 00Z.

There will be some scattered convection Friday afternoon and
evening, especially near KLAF. Will include a VCTS mention there.

&&

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

&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....JAS
AVIATION...50


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