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Area forecast discussion 
National Weather Service Indianapolis in
1155 PM EDT Wednesday Jul 27 2016

Update...
the aviation section has been updated below.

&&

Synopsis...
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 (rest of tonight and thursday)...

Issued at 943 PM EDT Wed Jul 27 2016

Only a few showers remain across the far southern forecast area
currently. Most of the convection is across far southern Indiana and
across Kentucky. Other scattered convection was across Illinois.

Convergence zone remains well south of the area at the moment, and
upper energy remains well south as well. Thus have kept pops
confined to the south third or so of the area for the remainder of
the evening.

Overnight a more southerly component /but still light/ will develop
in the winds and allow some of the convection to move north. Also,
some of the forcing from the upper system should impact the southern
area. Thus left overnight pops alone.

Made some adjustments to sky cover this evening as a mid deck has
developed. Tweaked low temperatures.

Previous discussion follows...

The models continue to differ on the role a weak boundary now over
the southern part of the County Warning Area 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 quantitative precipitation forecast 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
happen.

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
northwest flow thunderstorms as weak upper disturbances dive southeast 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 /discussion for 28/0600z taf issuance/...

Issued at 1155 PM EDT Wed Jul 27 2016

Conditions remain at VFR at this time with mainly mid to high clouds
from convection over the lower Ohio Valley. Radar showed a lone
-rash moving into kbmg before rapidly dissipating.

Areas of moisture extends from from the lower MS valley northward
into the Ohio Valley. Guidance continues to indicate that weak
boundaries over the Ohio Valley will drift northward overnight into
the morning hours. Challenge is that these boundaries are weak,
making it hard to focus where convection will develop over the next
6-12 hours. Thus, have gone with mainly thunderstorms in the vicinity through Thursday
morning over most areas.

&&

Ind watches/warnings/advisories...
none.
&&

$$

Synopsis...jk
near term...jk/50
short term...jk
long term....tucek
aviation...dwm

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