Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 180344
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1144 PM EDT Sun Sep 17 2017

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

&&

.SYNOPSIS...
Issued at 219 PM EDT Sun Sep 17 2017

A weak frontal system will move into the area tonight, and linger
into the middle of the week before dissipating. High pressure will
build into the area later this week and on into next weekend.

&&

.NEAR TERM /Overnight/...
Issued at 1014 PM EDT Sun Sep 17 2017

Convection from earlier this evening across the northwest half of
central Indiana had diminished extensively since sunset as the
activity moved into a much more stable airmass present further
south and east. Other than a few light showers...scattered convection
had focused back to the west over the Wabash Valley closer to the
weak instability axis and the approaching frontal boundary. 02Z
temperatures ranged generally from the upper 60s to mid 70s.

Main themes of the forecast for the rest of the night still hold
as the aforementioned frontal boundary tracks into the region in a
steadily weakening manner. Any thunder is likely to be focused
over western counties for the next 3 to 4 hours before instability
largely diminishes. While overall forcing aloft is not impressive...
presence of an approaching wave aloft in tandem with the
weakening frontal boundary should be enough to maintain a low
chance pop for most of the forecast area overnight. Will focus
highest chances over the northwest half of the forecast area.

Bumped up cloud cover late tonight for most of the area as well as
model soundings continue to highlight the potential for a shallow
inversion to develop. Patchy fog is also a possibility in the
predawn hours near daybreak...especially in locations that
received rainfall this afternoon and evening. Nudged lows up a
degree or two based on temperature trends so far this evening.

Zone and grid updates out.

&&

.SHORT TERM /Monday through Wednesday/...
Issued at 219 PM EDT Sun Sep 17 2017

Model guidance suggests a weak frontal system will get hung up in
the vicinity early in the period, before dissipating as upper
heights begin to rise towards the middle of the week. Although
nothing really stands out in the model data, the presence of the
weak surface boundary, moderate amounts of instability, and the
potential for weak upper waves to occasionally eject out of the
western long wave trough, suggests some threat for scattered
convection for most of this period. Will keep chance PoPs going
through Wednesday, although the precipitation threat will tend to
diminish towards the middle of the week.

Progged low level thicknesses suggest the GFS MOs temperature
guidance may be a little on the warm side on Tuesday and Tuesday
night. Will cut a few degrees off of the guidance during those
periods.

&&

.LONG TERM /Wednesday night through Sunday/...
Issued at 210 PM EDT Sun Sep 17 2017

Good confidence that the short term will see mostly or all dry
weather under the influence of surface high pressure and an upper
ridge per similar model output.

Also, good confidence that above normal temperatures will continue
per the blend. Look for highs in the mid and upper 80s and lows in
the 60s. Normal highs for early fall are in the upper 70s.

&&

.AVIATION /Discussion for 180600Z TAF Issuance/...
Issued at 1144 PM EDT Sun Sep 17 2017

Restrictions possible within convection through much of the
forecast period...more substantial lower ceilings and
visibilities possible near daybreak Monday.

Pockets of weakening showers continue to drift E/NE across primarily
the northern half of central Indiana late this evening. Expect a
continued threat for scattered showers through much of the overnight
as a weakening cold front drifts into the region from the west.
Cannot entirely rule out a few lightning strikes through the night
but little to no instability present does not support a thunder
mention at the terminals through daybreak.

Model soundings and RH progs continue to advertise the development
of a shallow inversion at or below 2kft towards daybreak...
especially over the northern half of the forecast area. These lower
ceilings will mix out as the morning progresses and the inversion
dissipates.

The arrival of an upper level wave on Monday combined with an
increasingly moist and unstable airmass will support renewed
scattered convective development...especially for the afternoon and
evening.

&&

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

&&

$$

SYNOPSIS...JAS
NEAR TERM...Ryan
SHORT TERM...JAS
LONG TERM...MK
AVIATION...Ryan



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