Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 200958

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

The AVIATION section has been updated below.


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 less forcing will be

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.
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 /Sunday Through Wednesday/...
Issued at 214 AM EDT Thu Jul 20 2017

Models are close enough that the model blend initialization
was accepted for most items.

An upper trough and surface cold front will bring chances for rain
to the area through Sunday night. Some models try and keep rain into
Monday, but with upper heights rising and the front south of the
area by sunrise Monday, feel that the day will be dry.

Rising upper heights and surface high pressure will keep Tuesday and
Wednesday dry.

Very warm temperatures Sunday will give way to near average
temperatures afterward.

Confidence is low to medium in rain chances Sunday/Monday but
is higher for dry weather Tuesday and Wednesday.


.AVIATION (Discussion for the 201200Z TAF Issuance)...
Issued at 558 AM EDT Thu Jul 20 2017

Outside of convection, VFR conditions expected as any lingering fog
will burn off quickly.

Mid and high clouds will continue across the TAF sites this morning
from thunderstorms to the north of the area. Thunderstorm complex
track/strength is uncertain for later this morning given effects of
earlier convection across the area. Will wait and see, but may have
to have some sort of mention at least at KLAF for early in the

More convection is possible this afternoon and evening as
instability returns and additional upper waves move across. At the
moment it looks like KLAF would be the most impacted, so will go
VCTS there.

More storms are possible again overnight tonight, especially north.
Coverage/location is much too uncertain to include in TAF that far

Overall confidence is low in the TAFs, especially north due to
uncertainty in thunderstorm development.




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