Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 222241

Area Forecast Discussion
National Weather Service Indianapolis IN
641 PM EDT Fri Sep 22 2017

Aviation Section has been updated below.


Issued at 310 PM EDT Fri Sep 22 2017

Unseasonable warmth for late September will continue through the
middle of next week as the Ohio Valley remains under the influence
of strong ridging at the surface and aloft. The passage of a cold
front on Wednesday will usher in much cooler air for late week.


.NEAR TERM /Rest of This Afternoon and Tonight/...
Issued at 310 PM EDT Fri Sep 22 2017

Have seen isolated convective development across the forecast
area since 17Z as a weakness present in the mid levels drifts by
to the south. Another hot afternoon in progress as Fall is set to
arrive. 19Z temperatures were in the upper 80s and lower 90s.

Primary focus initially is on any additional convective development
through the afternoon. Mid level cap and high pressure aloft and at
the surface are largely keeping a lid on convection. But as
mentioned...a weakness in the mid level flow is drifting southwest
through the Ohio Valley and likely serving as just enough of a
catalyst to generate isolated convection with the unstable airmass
and steep lapse rates courtesy of the strong surface heating. Will
carry a very low pop through early evening over most of the region
to account for any development. Bulk of the forecast area however
will remain and humid into the evening.

Remainder of the forecast for tonight will be quiet as any isolated
convection and diurnal cu diminishes towards sunset. Rest of the
night will see mainly clear skies. With light flow as well...expect
patchy fog to again form late tonight through daybreak Saturday.

Temps...another muggy night expected across the region as lows only
fall into the mid and upper 60s. A model blend worked well for
overnight lows.


.SHORT TERM /Saturday through Monday/...
Issued at 310 PM EDT Fri Sep 22 2017

Forecast challenges are few through what should be a quiet yet
continued very warm first weekend of Fall.

The presence of the remnants of Jose off the New England coast and
Hurricane Maria tracking north through the western Atlantic will
essentially maintain a blocky pattern over the contiguous U S. Deep
ridging aloft and a broad surface high pressure ridge will continue
to serve as the primary influences on weather not only across the
Ohio Valley but much of the eastern part of the country through the
weekend as a result. Both the ridging aloft and at the surface is
likely to strengthen a bit through Sunday and Monday as it drifts
southwest into the region.

Model soundings show the capping inversion strengthening through the
weekend and progressively drier air being drawn into central Indiana
from the east-northeast. This will effectively scuttle any diurnally-
driven convection through Monday and will likely limit cu formation
as well...especially compared to the last couple days. While it will
remain very warm...the advection of drier air will bring dewpoints
down steadily by Sunday and Monday...taking some of the mugginess
out of the air. Nights will remain comfortable as well.

Temps...will continue with persistence and run with highs above
guidance. Expect highs at or just above 90 again Saturday and
Sunday...possibly even Monday as well. Lows will slide back into the
lower and middle 60s with the arrival of the drier air.


.LONG TERM /Monday Night Through Friday/...
Issued at 213 PM EDT Fri Sep 22 2017

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

Warm conditions will continue early in the long term, then much
cooler will move into the area to end the work week.

Lingering upper ridging will keep the area dry Tuesday, but the cold
front with the much cooler air behind it will move through on
Wednesday bringing low chances for showers to parts of the area.
Current timing puts the front moving through when there should be
little instability, so continued to leave out any mention of thunder.

There is still some uncertainty on timing of the front which could
have impacts on rain chances if it changes. However, confidence is
high for the much cooler air moving in by late next work week.


.AVIATION /Discussion for KIND 230000Z TAF Issuance/...
Issued at 641 PM EDT Fri Sep 22 2017

With the exception of visibility restrictions from fog near
daybreak...VFR conditions are anticipated.

Isolated thundershowers will dissipate near or shortly after 00Z
with loss of daytime heating.   Then mostly clear overnight with
areas of fog towards sunrise at outlying TAF sites.  Will mention
tempo IFR for a few hours.  Then all fog will out after sunrise.
Expect a few CU again tomorrow.

Winds will be light through the period.





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