Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 261408

Area Forecast Discussion
National Weather Service Indianapolis IN
1008 AM EDT Fri May 26 2017

The NEAR TERM Section has been updated below.


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


.NEAR TERM /This afternoon/...

Issued at 1007 AM EDT Fri May 26 2017

Surface analysis early this afternoon shows a ridge of high
pressure over Indiana. GOESR shows a weak short wave over Iowa and western
Illinois. Weak southerly flow was in place across central Indiana
with dew points in the upper 50s.

Forecast soundings and time height section remain dry this
afternoon. the short wave to the west is expected to continue its
progression to the east...but best forcing still appears to remain
north of Central Indiana. HRRR suggests a dissipation of the rain
showers over Central Illinois upon approach. Furthermore forecast
soundings suggest convective temperatures in the lower 80s and
a strong mid level inversion.

Thus will trend toward a partly cloudy forecast along this
afternoon. Given the southerly flow and plentiful
sunshine...trended highs slightly warmer then the previous


.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 /Monday through Thursday Night/...
Issued at 349 AM EDT Fri May 26 2017

The main weather feature throughout the extended period will be
the broad low pressure system encompassing most of Ontario and
Quebec. Weak waves of energy will rotate through this system,
periodically triggering scattered showers and thunderstorms across
portions of central Indiana throughout the period. However,
precipitation chances will remain low throughout the period with
no higher than chance pops at any given time due to the
variability in the tracks and timing of the aforementioned waves.
Meanwhile, temperatures through the period will start out at or
above normal with a weak cooling trend on Tuesday and Wednesday,
then back to normal by Thursday.


.AVIATION /Discussion for the 26/1200Z TAF Issuance/...

Issued at 728 AM EDT Fri May 26 2017

MVFR/IFR fog conditions will linger for another hour or two and
then improve to VFR for today and evening. The main focus will be
the chance for showers and thunderstorms this afternoon through
tonight as a frontal boundary combines with upper waves.
Conditions will then fluctuate around the MVFR/IFR mark tonight.
Meanwhile, winds will be variable at 4 to 8 kts.




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