Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 151648

Area Forecast Discussion
National Weather Service Indianapolis IN
1248 PM EDT Tue Aug 15 2017

The AVIATION Section has been updated below.


Issued at 203 AM EDT Tue Aug 15 2017

Broad High Pressure will remain across Indiana and the Ohio Valley
today...providing more dry and warm summer weather. The high will
continue to keep warm and dry weather across Indiana through
Wednesday Morning.

A warm front will approach Central Indiana from the southwest on
Wednesday afternoon as low pressure develops across Minnesota and
Wisconsin. This will result in chances for showers and
thunderstorms through Thursday Night.

High pressure and more typical summer weather will build across
the region on Friday into the weekend.


.NEAR TERM /Rest of Today/...
Issued at 953 AM EDT Tue Aug 15 2017

Radar indicates a few showers over northern Indiana in association
with a weak frontal zone. Short term models suggest this feature
will sag south into the northern zones later this afternoon.
Stability analysis indicates a developing instability axis
over the northern zones as well. Given the above, will add some
small chance PoPs over the northern zones this afternoon. Don`t
really see anything to trigger organized activity today in the
upper air, so any activity that does develop should remain
isolated to widely scattered.

Previous discussion follows.

Surface analysis early this morning shows broad and disorganized
High pressure in place across The middle mississippi valley
stretching east to Indiana and Ohio. GOES16 shows high cloud
streaming across southern Indiana. Water vapor imagery shows
subsidence across Wisconsin and Northern Indiana as a short wave
was pivoting through the northern Great Lakes. Radar showed a few
isolated showers ahead of the subsidence over Northern Illinois.

GFS and NAM suggest the short wave dynamics to the north will
quickly exit east this morning....allowing the strong subsidence
over Wisconsin to build southeast. Meanwhile aloft...the models
suggest weak ridging over the Mississippi valley to build
eastward. Forecast soundings continue to show a dry column with
attainable convective temps. THus will trend with a dry forecast
given the lack of dynamics and expected subsidence ahead of the
approaching weak ridge. Will expect some afternoon and perhaps
some high clouds streaming within the upper flow as we have seen
in recent days.

Given the westerly flow and weak warm air advection will trend
highs at or above the forecast builder blend.


.SHORT TERM /Tuesday night through Thursday Night/...
Issued at 203 AM EDT Tue Aug 15 2017

Quiet weather looks to persist on Tuesday night through Wednesday
morning as ridging aloft moves across Indiana and the Ohio
Valley. Forecast soundings remain dry amid warm air advection.
THus will trend toward partly cloudy skies and temps at or above
the builder blend.

GFS and NAM suggest by Wednesday afternoon and evening the upper
ridging should be east of Indiana allowing short wave dynamics to
surge into Indiana by late afternoon. Forecast soundings here show
a significant moistening of the column by 21Z Wednesday as Pwats
surge toward 1.85. Forecast sounding also suggest attainable
convective temperatures and some minimal summertime CAPE values.
Thus will begin to ramp up pops during the afternoon hours into
the evening on Wednesday.

By Wednesday night the GFS and and suggests a more organized
short wave trough over the Mississippi Valley pushing eastward and
ejecting upper waves toward the Ohio Valley. The NAM appears a
bit more robust...and maybe overdone. However given the support
and moisture available...some chance pops will be needed on

Best chances for rain will arrive on Thursday and THursday night
as the models suggest the previously mentioned short wave will be
pushing across Central Indiana. Meanwhile...associated low
pressure over the Western Great Lakes will continue to deepen and
provide warm and moist southwesterly flow to Indiana as we will be
within the favorable warm sector. By Thursday evening/night the
GFS and NAm suggest a cold front pushing across the Indiana along
with the a more elongated and broad upper trough axis. Forecast
soundings on THursday show favorable conditions for afternoon
convection with CAPE over 3000 J/KG amid attainable convective
temps and a minimal cap. THus will ramp pops higher on Thursday
afternoon/evening when heating and forcing all come together.
Again given the ongoing warm air advection will trend temps at or
above the forecast builder blend expect on Thursday night in the
wake of the cold front.


.LONG TERM /Friday through Tuesday/...
Issued at 325 AM EDT Tue Aug 15 2017

Guidance over the long term is relatively dry, and the resultant
forecast is as well, although suspect that later consensus runs
may increase pops early in the weekend as an compact upper trough
moves through the Great Lakes. For now, though, will go with a
fairly dry forecast with surface high pressure in place across
much of the region through a significant portion of the long term.
Another somewhat more substantial frontal system moves toward the
area later in the period and will necessitate some thunder chances


.AVIATION /Discussion for the 15/18Z TAF Issuance/...
Issued at 1248 PM EDT Tue Aug 15 2017

Good confidence that VFR conditions with diurnal cu will dominate
through 06z or beyond. Then, with west and northwest winds becoming
light or calm, moderate to good confidence that MVFR fog will be
around from 09z or earlier to 13z at all or some of the terminals as
was the case earlier this morning. GFS LAMP supports this as well.

Could see a few storms around tomorrow as moisture increases with
winds shifting to the south in the wake of a front that is expected
to lift back to the north of the area. However, chances too low to
mention that many hours out with confidence not great on the




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