Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 202034
AFDIND

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

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
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.../Rest of This Afternoon and Tonight/
Issued at 253 PM EDT Sun Aug 20 2017

An old outflow boundary stretches across southern Illinois southwest
into Missouri early this afternoon. There were storms along this
boundary from the Mississippi river southwest, but nothing east of
it. Satellite shows not much cloud development along it, so think of
odds of storms developing in central Illinois and then moving into
the area are low.

Instability is building across the area currently even with cirrus
clouds moving across the area. However, organized forcing is
lacking. Thus, while cannot rule out an isolated shower or storm the
remainder of the afternoon, feel odds are too low to mention.

An upper disturbance (MCV) across northwest Illinois will move east
into the area this evening. Hi-res models are developing some
convection with this feature moving into western sections after 02Z
or so. Will include some low PoPs far west after 02Z.

Meanwhile, another upper disturbance currently across Iowa will move
into northern Indiana late evening into the overnight. An upper jet
will move in as well (though still relatively weak). These should be
enough to generate some scattered convection. Looks like best
forcing will remain across northern Indiana, so will only have some
slight chance PoPs across the north half or so of the area overnight.

The model blend looks good for temperatures given expected
conditions.

&&

.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
Tuesday.

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 /Update to KIND TAF/...

Issued at 432 PM EDT Sun Aug 20 2017

VFR through the period with winds SW to S winds below 10 knots.

Scattered cumulus will slowly dissipate leaving cirrus after dark.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...50
NEAR TERM...50
SHORT TERM...50
LONG TERM....Ryan
AVIATION...Tucek


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