Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 171052

Area Forecast Discussion
National Weather Service Indianapolis IN
652 AM EDT Thu Aug 17 2017


The Aviation section has been updated below.


Issued at 207 AM EDT Thu Aug 17 2017

Low pressure over the upper midwest will provide a warm and humid
southwest flow of air to Central Indiana today. This will result
in chances for showers and thunderstorms today. A cold front
associated with the low will pass through Indiana tonight ending
the rain chances.

Weak high pressure over the central Plains is expected to pass
across Indiana on Friday and and Friday evening...providing dry

A quick moving upper level weather disturbance is them expected
to sweep across the region overnight on Friday and early on
Saturday. This will result in another chance for showers and

The weekend will conclude and the next work week will start with
dry weather as large high pressure builds across the region.


.NEAR TERM /Today/...
Issued at 207 AM EDT Thu Aug 17 2017

Surface analysis early this morning shows low pressure in place
over Minnesota with a trailing cold front stretching southwest
across Iowa to western Missouri. GOES16 shows SW flow ahead of
this system streaming in to the Ohio Valley along with strong
convection across Oklahoma. National radar mosaics show more
showers over southern Missouri and a few isolated showers/storms
within the SW flow across Illinois and Srn Indiana.

Models remain in pretty good agreement today...keeping Indiana
within the warm and moist SW flow. Dew points across the area
remained in the very moist lower 70s. GFS 310k Isentropic surface
shows Central Indiana within an favorable lift area today with
specific humidities over 9 j/kg. Time height sections show a
saturated column amid lift...and forecast soundings show deep
saturation through the morning hours...suggesting rain with some
drying within the column by afternoon. Furthermore....forecast
soundings suggest some instability should convective temperatures
in the middle 80s be reached. By afternoon...CAPE soars to a
healthy 2800 j/KG. Thus if it fails to rain this morning...heating
and instability should lead to rain this afternoon. HRRR seems to
be taking the approach of pushing the more organized showers north
of the forecast area this morning and developing convection in
the afternoon.

Given all the favorable scenarios for rain will trend pops at or
above the forecast builder blend through the day. Confidence is
low for specific timing/location. Will stick close to the forecast
builder blend on highs.


.SHORT TERM /Tonight through Saturday Night/...
Issued at 207 AM EDT Thu Aug 17 2017

GFS and NAM show the best forcing...dynamics and moisture are
lost quickly this evening. The 310K GFS shows drying arriving
within subsidence by 03Z. Forecast soundings also show rapid
drying and stabilization within the column after 00Z. Best
forcing associated with the upper through to the north looks to
pivot to the east as a weak trough axis moves across Indiana. Thus
will keep some low pops prior to 03Z...particularly across the
eastern parts of the forecast area due to proximity. However...the
overall trend will be toward a dry forecast overnight. Will stick
close to the blend on lows.

GFS and NAM suggest high pressure and a dry column across the
area on Friday. Forecast soundings show a mid level inversion with
attainable convective temperatures that should lead to some flat-
topped afternoon CU. Thus partly cloudy with a blend on temps
will work fine.

The high will maintain control of the weather on Friday
evening...however both the GFS and NAm again suggest a secondary
upper wave pushing toward Central Indiana after 06Z
Saturday...before exiting by Saturday afternoon. Lower levels
respond by showing a weak surface trough passing across the area
sate wit this feature. forecast soundings also show a quick surge
of a saturated column. THus we will need to continue to include
pops for late friday night and early Saturday. Will trend toward
wetbulbs on Friday night.

By Saturday afternoon the models allow the short wave to quickly
exit as stronger ridging and high pressure build across the area.
Thus will trend toward a dry forecast for Saturday afternoon and
Saturday night.


.LONG TERM /Sunday through Thursday/...
Issued at 358 AM EDT Thu Aug 17 2017

Long term period looks dry save for the late Monday night through
early Wednesday time frame, when a low pressure system will move
through the Great Lakes. This will necessitate some chance pops
for showers and storms during that time period, with the highest
chances Tuesday into Tuesday night. Bumped some likelies down to
high chance given model fluctuations in the longer term, but
otherwise left blended initialization alone.

Consensus temperatures appeared reasonable. Should start on the
warmer side then see temperatures cool somewhat as the week wears
on and high pressure builds in behind the frontal system.


.AVIATION /Discussion for the 17/12Z TAFs/...
Issued at 647 AM EDT Thu Aug 17 2017

Largely VFR through the period. Some MVFR ceilings early in the
period at BMG, and then additional MVFR possible in showers and
storms later.

Frontal system moving through the area today may spark showers and
a few storms. Will carry these in the TAFs where
appropriate...storm chances will be higher at IND/BMG in the
afternoon than further west sites. Chances for showers and storms
will end this evening.

Winds will be 10KT or less throughout the period, generally
southerly early, becoming more southwesterly with time.





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