Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 200545
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
145 AM EDT Thu Jul 20 2017

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated below.

&&

.SYNOPSIS...
Issued at 145 AM EDT Thu Jul 20 2017

Hot, Humid and active weather is expected the through the end of
the work week. High pressure southeast of Indiana will continue to
allow a warm and humid air mass across Central Indiana. Meanwhile
aloft a quick moving Jet Stream flow through the upper midwest and
great lakes will push several upper level weather disturbances
into the region. This will result several rounds of showers and
thunderstorms that may push into Central Indiana through the start
of the weekend.

A cold front is expected to across our area late Sunday bringing
cooler, less humid and sunny weather for Monday into Wednesday.

&&

.NEAR TERM /Today/...

Issued at 145 AM EDT Thu Jul 20 2017

Large High pressure was in place across the Virginias...extending
westward across the Ohio valley to the Southern Plains. Radar
shows a cluster of thunderstorms over Lake Michigan and NW
central Indiana. Even more THunderstorms were developing across
the Plains states along a boundary stretching across Iowa and
Nebraska. A very warm and humid air mass was in place across
Central Indiana with dew point temps in the lower 70s. Water Vapor
showed a familiar stream of tropical moisture wrapping around
High pressure in the southern plains. The plume stretched across
the desert southwest across Nebraska to Wisconsin and the Great
Lakes.

Models remain in pretty good agreement keeping the High pressure
aloft in place across the Southern Plain...stretching toward
Kentucky and Tennessee. This results in a NW flow impacting the
Northern parts of Indiana...with several embedded short waves
poised within the tropical flow. Meanwhile...forecast soundings
today show convective temperatures in the lower 90s and copious
amounts of CAPE...over 3000 J/Kg. Pwats over 1.80. Thus daytime
heating along with any interaction with a short wave should result
in storms. Will include at least High chc pops across the
northern parts of the forecast area...which will be located closer
to the upper support. Will trend pops lower as one progresses
southward across the forecast area...as less forcing will be
present.

Regarding heat...clouds and possible showers across the northern
areas should prevent heat advisory criteria from being reached.
Better chances will be father south where clouds/rain/outflow
look to have less of a reach.

&&

.SHORT TERM /Tonight through Saturday Night/...

Issued at 145 AM EDT Thu Jul 20 2017

GFS and NAM suggest little change in the overall pattern through
Saturday Night. NW flow appears present aloft...allowing several
short wave to push across the southern Great Lakes and Northern
Indiana. Meanwhile...warm...moist and southerly flow remains in
place across Indiana with plenty of gulf moisture available.
forecast soundings each afternoon suggest steep lapse
rates...attainable convective temperatures and CAPE over 3000 J/KG
each afternoon. Overall confidence in precise timing of these
weak short waves is low. However with plenty of favorable
ingredients for storm development available through Saturday
nigh...a dry forecast will not be possible. Will keep at least chc
pops in place during each period due to expected passing
dynamics...diurnal heating and plentiful moisture. Again...best
chances will be across the northern parts of the forecast area
where dynamics should be best.

Given the expected warm air advection will trend Highs and lows at
or above a forecast builder blend.

&&

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

Issued at 214 PM EDT Wed Jul 19 2017

A look at the GFS Ensembles show the basic idea of the main band
of westerlies remaining over the northern third of the U.S. The
European model also went this direction so we have some basic
consistency in the models so far. Both models bring a threat of
showers/thunderstorms with a cold front Saturday night and Sunday
morning as the mid/upper level ridge retrogrades back west into
the Plains. But, then high pressure moves southeast into the Great
Lakes region. The blend brings a slower clearing than expected
compared to the other models and feel it is going to be faster.
Monday into Tuesday look like pretty nice days bringing
temperatures closer to normal which is the mid 80s for highs and
upper 50s for lows to start the new work week.

While basically northwest flow aloft comes back into the picture by
midweek, looks like another chance of precipitation for the area.
The GFS still has high pressure centered over the region on
Tuesday, but Euro brings what looks like a MCS into the mid
Mississippi Valley by Wednesday morning. Not very sure about this
at this time.

Confidence: Medium through the weekend and early week.
            Low Tuesday afternoon and Wednesday.

&&

.AVIATION /Discussion for 200300z TAF issuance/...

Issued at 1045 PM EDT Wed Jul 19 2017

Updated current conditions only. Previous discussion follows...

Moist airmass and light winds will likely lead to fog again
tonight at all but KIND similar to last night. Expect to see this
develop around 5-7z and then see improvement back to VFR by around
11-13z. At KIND think heat island effect will keep low temperature
up a bit and thus have higher dewpoint depression here. While
there is currently some widely scattered convection west and
northwest of KLAF, at this point it looks like this will remain
outside of even the 10 mile radius of the airport so will leave
out. Winds should be light to calm overnight but then climb to
around 6-10 kts out of the southwest during the day on Wednesday.
There is also currently a large storm complex over NE Iowa/SE
MN/SW WI that possibly could impact KLAF late during the
overnight, but at this time it looks like this will stay north of
the site and will leave out as well.


&&

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

$$

SYNOPSIS...Puma
NEAR TERM...Puma
SHORT TERM...Puma
LONG TERM....DWM
AVIATION...CP



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