Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 152242

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

Aviation Section has been updated below.


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

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

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 16/00Z TAF Issuance/...
Issued at 642 PM EDT Tue Aug 15 2017

Mainly VFR...although a period of IFR fog possible towards sunrise
mainly KLAF.  Scattered thunderstorms are also possible west and
southern sections by midday Wednesday.

High pressure over the northern great lakes will move on to the
east as low pressure over the central plains moves into the
upper midwest.  This will pull a warm front north into our region
by Wednesday.  There was areas of fog last night at outlying TAF
sites and there should be enough radiational cooling for more fog
mainly north tonight.

Otherwise...expect few to scattered Cu overnight and VFR ceilings
developing Wednesday.   Models spread scattered showers and thunder
storms into west central and south areas Wednesday and then spreading
north Wednesday night.

Winds will be light through the period.




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