Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 202304

Area Forecast Discussion
National Weather Service Indianapolis IN
704 PM EDT Sun Aug 20 2017

The NEAR TERM and AVIATION Sections have been updated below.


Issued at 253 PM EDT Sun Aug 20 2017

A few upper waves will bring chances for thunderstorms tonight into
Monday, before a cold front brings better chances for rain Monday
night into Tuesday evening. Dry conditions will then prevail mid
week into next weekend. Hot and humid conditions to start the week
will give way to below normal temperatures mid week on.


.NEAR TERM /Tonight/...

Issued at 646 PM EDT Sun Aug 20 2017

Isolated thunderstorms will continue to track east southeast
in the East Fork White River valley through sundown.

Satellite indicating towering cumulus near or
two might reach shower stage but for the moment will keep Indy
forecast dry this evening.

High resolution models now seem to be picking up correct trend
that convection will not develop in eastern Illinois and track
into Indiana later this evening. Will likely update next forecast
to remove this potential if radar and satellite and short range
models continue to show this same outcome of staying dry.


.SHORT TERM.../Monday through Wednesday/
Issued at 253 PM EDT Sun Aug 20 2017

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

There could be some lingering convection across the far north at the
start of the Monday period so will keep some slight chance PoPs
there early. After a brief lull, more scattered convection is
possible as yet another upper disturbance moves in. Looks like the
best forcing remains north, so will keep PoPs across the northwest
2/3 of the area or so and keep them in chance category or lower,
with the highest PoPs in the afternoon when instability is highest.

Next concern is then sky cover for the eclipse. Have real concerns
that mid and high clouds will impact the event and reduce the
chances of having a good view. Models have been trending up sky
cover at 18Z with each run. However, confidence is low in sky cover
for the eclipse window as timing of any convection and exact
location of thicker high clouds is hard to pinpoint. Will keep skies
partly cloudy (50-70% coverage of opaque clouds) for now.

A cold front will then approach the area Monday night and move
through Tuesday. Forcing will be decent with upper jet support and
decent 850mb flow. However, timing for convection isn`t that great
as front moves in when instability is lower due to time of day. Rain
could be in the weakening phase as it moves in Tuesday morning then
get stronger again south of the area when instability is maximized
later Tuesday afternoon. For now though timing looks good enough for
the threat of strong to severe storms across mainly the southern
half of the area Tuesday afternoon.

Still feel there will be enough rain around to measure at least 0.01
inch most areas so will keep the blend`s likely category PoPs

Will keep some low PoPs Tuesday evening to account for any lingering
rain behind the front. High pressure will then build in and bring
dry conditions later Tuesday night through Wednesday.

Model blend temperatures look good. Heat indices could reach around
100 Monday afternoon if cloud cover is thin enough.


.LONG TERM /Wednesday Night through Sunday/...
Issued at 201 PM EDT Sun Aug 20 2017

Splendid stretch of late summer weather for the extended period as
the Great Lakes and Ohio Valley reside under a broad upper trough
and strong high pressure at the surface for much of the period.
With dry low level flow from the north then east...expect days
full of plentiful sunshine and mainly clear nights with no
threats of rainfall. High temperatures will be pleasant...ranging
from the mid 70s to lower 80s Thursday through Saturday. Nights
will have a distinct autumn feel with temperatures dropping as low
as the lower and middle 50s.

Heights aloft will recover with the upper trough shifting off to
the east by Sunday. The region will remain under the influence of
a surface ridge...but low level flow will transition to southerly
on the back side of the high...resulting in temperatures warming
into the lower to possibly middle 80s on Sunday. Not entirely out
of the question that a potential for isolated convection would be
present by late weekend with moisture being advected north into
the Ohio Valley...but chances too remote at this point for
inclusion into the forecast.


.AVIATION /Discussion for 210000Z TAFs/...

Issued at 646 PM EDT Sun Aug 20 2017

VFR with south to southwest winds below 10 knots through the

Daytime heating cumulus will dissipate after sunset Sunday but
still patches of mid level and high level precipitation remnant
cloud debris across Illinois to move into Indiana overnight.

Another minor trough in the upper flow will enhance cumulus cloud
development again by 211800z with isolated thunderstorms perhaps a
potential during peak heating Monday.




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