Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 230433

Area Forecast Discussion
National Weather Service Indianapolis IN
1233 AM EDT Fri Jun 23 2017

The AVIATION Section has been updated below.


Issued at 130 PM EDT Thu Jun 22 2017

High pressure est of Indiana will exit the area tonight. A
tropical low pressure system over the lower Mississippi Valley
will surge northward tonight...bring rain showers to Central
Indiana for late tonight and Friday. Heavy rain will be possible
with some of the rain showers as the low moves through the Ohio
valley on Friday.

As the low departs on Friday night...dry weather is expected to
return to Central Indiana for the weekend as cool high pressure
settles across the Great Plains. This will result dry weather for
the weekend.

The large high will remain the dominate weather feature for much
of the next work week. This will keep mainly dry weather with
below normal temperatures through next week.


.NEAR TERM /Overnight/...
Issued at 930 PM EDT Thu Jun 22 2017

Scattered showers expected to linger over the southern zones for a
couple more hours as a mid level vorticity lobe drifts northeast
through southern Indiana.

Better threat for shower and thunderstorm activity expected to
develop during the pre dawn hours of Friday, as a southwesterly low
level jet of 35-40 kts begins to interact with a frontal system
dropping south through the Great Lakes.

Current forecast handles this idea well, with the highest PoPs
before dawn. Increased the wind forecast a bit based on current

Previous discussion follows.

Surface analysis early this afternoon shows Low Pressure in place
across Louisiana. Warm and moist southerly flow was spilling
northward into the Ohio Valley ahead of the low pressure system.
GOES16 shows plentiful moisture streaming northward ahead of the
low. Meanwhile to the north...a cold front stretched across
Western Wisconsin and Iowa to Nebraska...progressing
southeastward. These two systems will be on a collision course for
the Ohio Valley Tonight and Friday.

Forecast soundings and Time Height remains mostly dry this evening
across Central Indiana. Models suggest a slow and steady
saturation of the column through the evening hours which should
just be increasing clouds. However...overnight...stronger lift
arrives as seen within the mid levels...particularly across the
southern half of Indiana. Lower level Q vectors also indicate
good convergence developing late tonight and HRRR suggests precip
arriving from the southwest associated with the low. Furthermore
as the front arrives in the area front the northwest late
tonight...and interacts with the warm and moist air mass across
Indiana...precip chances will continue to increase. Forecast
soundings by 12Z show deep saturation with very high pwats over 2

Thus summing up will try and keep evening dry across Central
Indiana...but trend pops toward 100 overnight...particularly
across the south. Pops will be considerably lower farther north as
interaction with the tropical air mass will be less at those
locations. Given the expected rain and ongoing warm air advection
will trend lows toward expected wet bulb temps.


.SHORT TERM /Friday through Sunday/...

Issued at 130 PM EDT Thu Jun 22 2017

Ample dynamics will be in place on Friday for rain...some of which
could be heavy at times. The GFS suggests the approach of the
tropical low...reaching western Kentucky by late afternoon. Warm
and moist southerly flow will continue to stream into the Ohio
valley on Friday. Models continue to suggest excellent lower level
Q vector convergence. Forecast soundings show deep saturation and
Time heights also show excellent lift...particularly across the
southern half of the state. Forecast soundings also show pwats
remaining at or near 2 inches through much of the afternoon. Thus
given the dynamics and available moisture will include a FLASH
FLOOD WATCH for the southern parts of Central Indiana. Given the
expected rain...will trend highs cooler than MAVMOS.

GFS and NAm suggests the upper flow keeps a broad yet shallow
trough in place aloft on Friday night through Sat least sunday
across Indiana and the Great Lakes. This flow aloft will help to
quickly usher the tropic low east of the Ohio valley on Friday
Night. Cool and dry northwest surface flow will replace previous
flow on Friday Night and continue into the weekend. Forecast
soundings and Time height show rapid drying on Friday night as the
Low and associated forcing departs. Thus may keep a small pops on
Friday night...mainly across the southeast as the system
departs...however most of the area will remain dry. Given the
change in air mass...will stick close to the blend on lows.

Saturday through Sunday should remain dry. forecast soundings show
a dry column. Convective temperatures appear reachable...however
a mid level inversion that appears to be present should prevent
any deep cumulus growth. A the weak broad trough will remain in
place aloft...but organized forcing fails to be seen and moisture
remains lacking with NW flow. Thus will trend toward partly clouds
this period. Given the expected cold air advection and...may
trend temps cooler than blends.


.LONG TERM /Sunday through Wednesday/...

Issued at 400 AM EDT Thu Jun 22 2017

Models continue to trend toward a drier forecast for the extended
period. The only chances for a few showers and thunderstorms will be
on Sunday and Monday afternoons, mainly over the northern counties,
as a few upper waves move through the area. Otherwise, expect dry
conditions throughout the extended period with a gradual warming
trend. Highs will start out in the 70s on Sunday and Monday,
eventually topping off in the low to mid 80s by Wednesday.
Meanwhile, overnight lows will increase from the mid 50s on Sunday
night to low/mid 60s by Wednesday night.


.AVIATION (Discussion for 20600Z TAFs)...

Issued at 1234 AM EDT Fri Jun 23 2017

Shower and thunderstorm activity expected to increase in the
vicinity of the terminals towards/after sunrise Friday as a
southwesterly low level jet of 35-40 kts interacts with a frontal
system dropping south through the Great Lakes. IFR visibility
restrictions probable in the heavier precipitation areas.

IFR ceilings 006-009 AGL should continue to spread over the
terminals from south to north overnight under a warm and moist
advection pattern. These ceilings may tend to lift into an MVFR deck
towards midday Friday as the boundary layer heats up.

Surface winds 180-210 degrees at 7-11 kts overnight will gradually
veer around to 220-260 degrees towards midday Friday. Occasional
gusts 18-20 kts possible towards midday Friday as well.


Flash Flood Watch from 8 AM EDT this morning through this
evening for INZ052>057-060>065-067>072.



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