Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 151828
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
228 PM EDT Tue Aug 15 2017

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated
below.

&&

.SYNOPSIS...
Issued at 225 PM EDT Tue Aug 15 2017

A frontal system is expected to affect the area on Wednesday and
Thursday. In the wake of this system, high pressure is expected to
move into the area for the weekend and on into early next week.
Another front may affect the area towards the middle of next week.

&&

.NEAR TERM /Rest of This Afternoon and Tonight/...
Issued at 225 PM EDT Tue Aug 15 2017

A weak frontal zone will continue to sag south into the northern
zones later this afternoon and evening, eventually reaching
southern Indiana by sunrise Wednesday. An instability axis in the
vicinity of the front may spark off some isolated shower activity
through about sunset, mainly over the northern zones. Weak flow at
850mb and no discernible upper air feature tonight suggests any
activity that develops near the front will be mostly diurnal in
nature.

Some fog possible late tonight as expected lows will be near current
dewpoints.

Low level thicknesses suggest the GFS MOS lows tonight look good,
with little if any adjustments planned.

&&

.SHORT TERM /Wednesday through Friday/...
Issued at 225 PM EDT Tue Aug 15 2017

Convective potential expected to increase by Wednesday and Wednesday
night as a warm advection pattern develops in advance of a short
wave trough moving towards the Midwest. This threat expected to
continue into Thursday night as the upper trough drifts into the
Great Lakes, accompanied by an associated cold front. Overall severe
potential looks low at this time, given poor lapse rates and weak
deep layer shear. However, heavy rainfall is possible as models
suggest precipitable water in excess of 2 inches over the area by
Wednesday afternoon through Thursday. Will go with PoPs in the
Wednesday through Thursday night periods.

May need to keep a PoP in the forecast over the far eastern zones
Friday morning as the system is exiting, but overall conditions
should improve with time during the day Friday.

Progged low level thicknesses suggest the GFS MOS highs for
Wednesday may be a little on the cool side. Will bump up the
guidance numbers a bit in that period. Otherwise, the guidance
numbers look OK.

&&

.LONG TERM /Friday night through Tuesday/...
Issued at 205 PM EDT Tue Aug 15 2017

Long range challenges will center around the possibility of adding
pops for Saturday and Saturday night as a sharp upper trough moves
through the area. All the deterministic models are keying more in on
the possibility of convection Saturday and Saturday night per their
QPF fields leading to improved confidence. In addition, the blend
has also come along regarding pops. Finally, another frontal system
could bring more thunderstorms to the area by next Tuesday.
Otherwise, high pressure should provide a mostly dry long term.

Low level thermal progs suggest near normal temperatures with highs
in the 80s and lows in the 60s per the blend. This looks reasonable
with average confidence.

&&

.AVIATION /Discussion for the 15/18Z TAF Issuance/...
Issued at 1248 PM EDT Tue Aug 15 2017

Good confidence that VFR conditions with diurnal cu will dominate
through 06z or beyond. Then, with west and northwest winds becoming
light or calm, moderate to good confidence that MVFR fog will be
around from 09z or earlier to 13z at all or some of the terminals as
was the case earlier this morning. GFS LAMP supports this as well.

Could see a few storms around tomorrow as moisture increases with
winds shifting to the south in the wake of a front that is expected
to lift back to the north of the area. However, chances too low to
mention that many hours out with confidence not great on the
coverage.

&&

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

$$

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


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