Area Forecast Discussion
Issued by NWS Indianapolis, IN

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394
FXUS63 KIND 230426
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1226 AM EDT Sun Jul 23 2017

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

&&

.SYNOPSIS...
Issued at 338 AM EDT Sat Jul 22 2017

Central Indiana will remain on the edge of a strong upper ridge
through tonight....maintaining hot and exceptionally humid
conditions. Chances for thunderstorms will continue until a frontal
boundary can push through the area overnight into early Sunday. A
secondary front may bring additional scattered storms on Sunday
evening before high pressure builds in with mainly dry weather and
seasonable temperatures for the early part of the week.

&&

.NEAR TERM /Rest of Tonight/...

Issued at 907 PM EDT Sat Jul 22 2017

Question of the evening is when and how much thunderstorm activity
will occur overnight. Latest mesoscale analysis shows an old
convective boundary that extends from southwest OH west through
Monroe county then southwest through Sullivan county. But, there
is also a slow moving front that will be moving towards western IL
that could result in developing more thunderstorms overnight.

MLCAPE of 4500 J/kg exists over central IL with 2500 J/kg
extending into the southwest counties. The HRRR has been
developing storms over IL much of the evening, but those have not
occurred at this time. So, will continue to forcast thunderstorms
overnight but it seems the probabilities may be a little lower
than earlier. Thunderstorms that do develop could produce frequent
lightning and heavy downpours and could possibly last towards
daybreak.

Warm and humid for one more day before high pressure can move into
parts of the area for a more comfortable Monday.

&&

.SHORT TERM /Tonight through Monday Night/...
Issued at 338 AM EDT Sat Jul 22 2017

Forecast challenges focus on precip chances...especially tonight and
again late Sunday and Sunday evening.

Convection will likely be ongoing this evening as development takes
place over northern counties and progresses southeast through the
evening and overnight ahead of the cold front.  A surface wave along
the boundary...continued influence of a low level jet...BL shear
values around 30kts and a strongly unstable airmass all support a
threat for severe storms this evening gradually transitioning into
more of a heavy rain threat overnight. Highest pops will be employed
over the eastern half of the area where parameters will be just a
bit more favorable for more widespread convection. Precip water
values will remain above 2 inches and combined with freezing levels
near 15kft supporting warm rain processes...torrential rainfall and
flooding will continue to be concerns as the storms surge south
overnight.

Growing confidence that most if not all of the convection will be
out of the forecast area by 12Z Sunday with the front settling south
of the Ohio River.  Much of the day Sunday should be dry with an
edge being taken off the humidity levels. A secondary front
associated with a sharp upper wave diving out of the western Great
Lakes may serve as a focal point for renewed convective development
to the northwest of the region Sunday afternoon...possibly spreading
into the northern half of the forecast area during the evening.
Steep mid level lapse rates in response to cooling aloft suggestive
that strongest storms may carry a damaging wind and large hail
threat.  Will bring low chance pops back into the northern counties
Sunday evening as a result.

Convection will diminish overnight Sunday with high pressure
building south into the region on Monday with cooler and noticeably
less humid air. Likely to see diurnal cu develop on Monday before
skies become mostly clear Monday night.

Temps...it will remain very warm on Sunday with low level thermals
supporting highs from the mid 80s to around 90. Temps will fall back
into the lower and middle 80s Monday with cooler air aloft advecting
into the region. Lows will slide back into the 60s through the
period.

&&

.LONG TERM /Tuesday night through Saturday/...

Issued at 220 PM EDT Sat Jul 22 2017

The long term begins with central Indiana under the influence of
upper ridging, thus resulting in warming temperatures and dry
weather Tuesday night through early Wednesday night. By late
Wednesday night some model runs indicate the ridge could begin to be
suppressed as an upper wave travels through to the northwest and
thus bring a chance for thunderstorms back into the forecast on
Thursday. Friday currently looks like a cold front will move through
the area, and have chances for thunderstorms dropping off in its
wake. Result is thunderstorm chances Thursday through Friday with
dry conditions building in by Friday night. Long term temperatures
will peak on Wednesday with highs in the upper 80s to lower 90s
before dropping a couple degrees on Thursday due to cloud cover and
another degree or two for Friday with the cold front moving through.
Medium confidence in the return of storm chances late in the week,
and in cooler temperatures (low to mid 80s).

&&

.AVIATION (Discussion for 230600Z TAFs)...

Issued at 1226 AM EDT Sun Jul 23 2017

Radar shows thunderstorms from HUF east and southeast through areas
between IND and BMG through LUK/CVG. IR satellite imagery shows new
development now over east central MO/w central IL and this activity
will continue to move through the southern half of the area Sunday
morning. Thus expect occasional VLIFR in the vicinity of these
thunderstorms with IFR/MVFR north in areas like LAF and MIE.

Activity is expected to clear to VFR/occasional MVFR between 11Z and
14Z for Sunday morning.


&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...DWM
SHORT TERM...Ryan
LONG TERM....CP
AVIATION...DWM/JK



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