Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 201659

Area Forecast Discussion
National Weather Service Indianapolis IN
100 PM EDT Thu Jul 20 2017

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 /Rest of Today/...
Issued at 1030 AM EDT Thu Jul 20 2017

A weakening thunderstorm complex had spread into the northern half
of central Indiana late this morning.  As a result have increased
rain chances to likely across northern sections and to high chance
POPS as far south as INDY in the next few hours.  Rapid refresh
model slowly dissipates this complex over the next several hours.
But in previous runs it has been too quick to do this.  Will keep
higher POPS into early afternoon.   After that I would not be
surprised if it dies out...but confidence is low so will keep 20-30%
chance POPS across our northern half.

Previous forecast lowered temperatures some over most areas and will
continue that trend with this update.   Far SW sections will see
more sun and this may allow highs to approach the middle 90s there.
This in combination with high dewpoints should produce heat index
values to rise to near 105 degrees.   Will issue a heat advisory for
this afternoon through Saturday for Sullivan...Knox...Daviess and
Martin counties.


.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 201800 TAF Issuance)...
Issued at 100 PM EDT Thu Jul 20 2017

Shower and thunderstorm complex over east central Indiana will
move on to the east.   Quiet weather should occur the rest of the
afternoon and early tonight.  Several models indicate more storms
may develop along a weak frontal system moving into northern Indiana
by late evening and affect the northern portions of central Indiana
overnight.   Confidence on timing is low and will mention a period
of VCTS at KLAF from 03Z to 06Z tonight.   Could affect IND TAF as
well...but chances and confidence on timing is too low to add at
this time.

Otherwise...It will be VFR with few to scattered CU and Scattered
to broken mid clouds.   Will mention a period of MVFR fog at KLAF
very late tonight through 12Z.

Winds will be southwest up to 8 knots this afternoon and variable
around 5 knots most other periods.


Saturday for INZ060-067>069.


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