Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 272032

Area Forecast Discussion
National Weather Service Indianapolis IN
430 PM EDT WED JUL 27 2016

The AVIATION Section has been updated below.


Issued at 137 PM EDT Wed Jul 27 2016

The same weak frontal boundary is going to keep Indiana weather
unsettled into next week.The boundary will shift so sometimes it
will be a bit north of our state and other times slightly to our
south. Either way, it should control what happens here.


.NEAR TERM (Tonight and Thursday)...

Issued at 137 PM EDT Wed Jul 27 2016

The models continue to differ on the role a weak boundary now over
the southern part of the CWA will play. There is at least agreement
it will probably rain in the south tonight into tomorrow.

Flood guidance there is low. Currently no model has enough QPF to
indicate a Flash Flood Watch is needed, but one may be required
later depending on exactly how much rain develops.

Farther north, chance POPs reflect the uncertainty about what will

Both the underlying and derived temperature fields are close,
supporting use of a blended forecast. Temperature forecasts could
be wrong by several degrees in few places depending on just when
thunderstorms occur.

There will be ample moisture for partly cloudy skies due to
diurnal cumulus.


.SHORT TERM (Thursday night through Saturday)...

Issued at 137 PM EDT Wed Jul 27 2016

The models agree about a weak boundary over the area controlling the
weather.  They don`t agree on critical details and can`t be expected
to for such a subtle feature. Confidence in this forecast is low
especially for rain chances.

A blended forecast will minimize errors with both temperatures and
rain chances.  Expect temperature changes of 3-5 degrees and POP
changes of 30 or more in updates.

Skies will be partly cloudy. A definite part of the forecast is
conditions favoring diurnal cumulus.


.LONG TERM /Saturday night through Wednesday/...

Issued at 142 PM EDT Wed Jul 27 2016

The pattern undergoes a shift from sluggish flow and weak
troughing in the eastern half of the US to an exit of this trough
and subsequent upper ridge building forced by a fairly strong
system crossing southwest Canada. The most predictable outcome for
this is a shift towards warmer temperatures next week though not
back to the 90s. Another will be the return of 70 degree dewpoints
as southerly flow gets re-established. Less certain outcomes
relate to precipitation chances. With the upper trough still
present at the start of this period...shower chances will
continue. As this ridge departs Sunday night appears to be dry.

By Monday upper ridging takes place to our west. A surface warm
front sets up to our west as well. This brings the potential for
NW flow thunderstorms as weak upper disturbances dive SE over the
top of the ridge and interact with the warm and unstable air near
the surface warm front. The question is whether this action stays
west of us or whether the ridge builds far enough east that these
storm clusters affect Indiana. With high uncertainty have
introduced superblend low chance pops for this potential.

Temperatures forecast will be near current values and remain near
normal to start and trend slightly above normal for Monday onward.


.AVIATION /Update Discussion for 271800z TAFs/...

Issued at 430 PM EDT Wed Jul 27 2016

VFR conditions are the rule this afternoon. Weak quasistationary
boundary remains from SE OK into southern IL then east along the
Ohio River.  Satellite imagery/Radar shows scatter -TSRA along the
souther part of central IN and will have to monitor whether these
will effect KBMG over the next 6 hours.

Previous Discussion...

Winds will be light and variable through the forecast with a
diffuse frontal boundary in the area. Mainly VFR conditions are
expected during this TAF period though potential IFR fog and
ceilings could develop at KBMG and KHUF after 280600z.

The TAF sites are still in a moist tropical flow aloft.
Surface pressure gradients are weak and thus the light and
variable wind direction. Model soundings still show a mid level
inversion across the area which will impede significant
convection from occurring.

Light wind and mid cloud passing overhead at times tonight
may lead to some localized fog toward daybreak.

Models lift a weak surface low into the lower Ohio Valley
by daybreak and this will lift scattered light showers back
towards all sites except KLAF. Eventually this low rain threat
will also spread toward KLAF by 281400z.


.IND Watches/Warnings/Advisories...


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