Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 240812
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
412 AM EDT Mon Jul 24 2017

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 315 AM EDT Mon Jul 24 2017

A much needed break from the stormy...hot and humid conditions
experienced recently begins today as high pressure builds into the
area from the north. Expect dry weather with cooler and less humid
air through midweek. Low pressure will track into the region late
Wednesday night and Thursday bringing the threat for thunderstorms
and heavy rainfall. High pressure will reestablish by late week with
dry and seasonable conditions into the weekend.

&&

.NEAR TERM /Today/...
Issued at 315 AM EDT Mon Jul 24 2017

Cold front pressing south through the forecast area early this
morning as the leading edge of cooler and less humid air. The front
as of 07Z generally extended from near Richmond W/SW to just north
of KBMG to near Sullivan. Have seen a few tiny showers develop in
the vicinity of the boundary east of the Indy metro...but generally
conditions are dry. 07Z temperatures generally ranged from the mid
60s to the lower 70s.

The frontal boundary will continue to drift south through the
predawn hours and should be south of the forecast area shortly after
daybreak. Cannot entirely rule out a stray shower near and south of
the front over the next few hours but overall expecting a dry
passage of the front across southern counties this morning.

High pressure centered over the upper Midwest will expand south
today and finally spread a drier and cooler airmass into central
Indiana. Dewpoints will slowly drop through the 60s with a
progressively more comfortable feel to the airmass. It will
certainly be a nice change from the very warm and oppressive feel to
the air over the last several days. Convective temperatures in the
lower 80s and expanding cold advection support cu development over
the region this afternoon. Northerly winds up to 10mph are expected.
Enjoy the beginning of a nice break from the active...stormy weather
of late.

Temps...low level thermals are supportive of highs ranging from the
upper 70s north into the mid 80s over the lower Wabash Valley. An
overall model blend matched these thoughts well.

Overall forecast confidence is high today.

&&

.SHORT TERM /Tonight through Wednesday Night/...
Issued at 315 AM EDT Mon Jul 24 2017

Forecast challenges focus on precip chances developing Wednesday
night ahead of low pressure tracking into the lower Great Lakes.
Forecast confidence is high through Wednesday...then medium
Wednesday night with the threat for rain and storms.

The high pressure will drift across the Great Lakes maintaining a
dry...pleasant weather pattern over central Indiana into Wednesday.
E/NE low level flow will bring even lower humidity through Tuesday
and Tuesday night with mainly clear skies anticipated. Model
soundings still favor potential for a few cu Tuesday afternoon...
likely flattened beneath a strong capping inversion. But overall
will see abundant sunshine Tuesday and the first half of Wednesday
with the surface high serving as the dominant influence on our
weather.

Surface flow will veer around to a more southerly direction
Wednesday as the high moves to the East Coast. The cold front
passing through the area this morning will return north into the
lower Ohio Valley on Wednesday in response to low pressure tracking
E/NE through the central Plains and Missouri Valley and mid level
heights rising again as the upper ridge shifts back to the east into
the southern Plains. It is conceivable that the close proximity of
the approaching warm front could spark isolated convection over the
lower Wabash Valley Wednesday afternoon but have left any mention of
rain out of the forecast at this time with model soundings
indicating the cap will only weaken slowly.

The cap will erode from west to east Wednesday night as the front
lifts into the area and the low pressure tracks into the lower Great
Lakes. The model consensus with the exception of the NAM is hinting
at a slower eastward progression to the storm system which is
preferred at this time with the surface ridge giving way only slowly
to our east. The presence of a 40-45kt+ low level jet nosing into
the region combined with diffluence aloft supports an increasing
threat for convection Wednesday night...likely becoming widespread
towards daybreak Thursday. Precip water values surging over 2 inches
by early Thursday strongly suggest heavy rainfall and possibly
flooding will again become concerns for the forecast area late
Wednesday night into Thursday. Freezing levels rising back above
15kft also support this thinking with warm rain processes in play.

Temps...nice stretch of weather forthcoming with highs mainly in the
80s.  Could see southwest counties make a run at 90 degrees
Wednesday as the return flow develops and humidity levels begin to
rise again. Overnight lows tonight and Tuesday night will range from
the upper 50s to lower 60s then return closer to 70 for Wednesday
night. An overall model blend was followed through the period.

&&

.LONG TERM /Thursday to Sunday/...
Issued at 218 AM EDT Mon Jul 24 2017

Confidence is high the period will start wet and end dry.

Rain is probable at some point from Thursday into Friday.  Both the
American and European models bring precipitation with a front. Exact
timing is uncertain with the American system taking the front
through more rapidly.

From Friday night through Sunday both models are dry.

POPs from today`s forecast may be off by 10-20 percent Thursday to
Friday.  Friday night to Sunday, POPs should be off less than 10
percent.

With uncertainty about precipitation, there is uncertainty about
temperatures Thursday into Friday.  The consensus forecast could be
off by 5 degrees. The models align Friday night to Sunday. Errors
should be 3 degrees or less.

&&

.AVIATION (Discussion for 240900Z TAF update)...

Issued at 412 AM EDT Mon Jul 24 2017

With clearing, light winds and low level moisture from yesterdays
storms there may be MVFR or worse 10Z-13z. After 13z, should just
see some fair weather VFR cu.

Winds will be light overnight and north 7 knots or less after
14z.

&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....JK
AVIATION...MK/JK


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