Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 181630

Area Forecast Discussion
National Weather Service Indianapolis IN
1230 PM EDT Fri Aug 18 2017

The AVIATION Section has been updated below.


Issued at 308 AM EDT Fri Aug 18 2017

Partly cloudy skies will provide dry weather today. However,
thunderstorm chances will return overnight and Saturday as an upper
system pivots across the lower Great Lakes and Ohio Valley. After
that, high pressure will bring dry weather back for the remainder of
the weekend and next Monday. The threat for thunderstorms will
return next Monday night through Wednesday as a cold front moves
across the area from the northwest. Finally, high pressure will
bring dry and cooler conditions to the area through remainder of
next week.


.NEAR TERM /Rest of Today/...
Issued at 1008 AM EDT Fri Aug 18 2017

Pleasant morning ongoing with surface high pressure over the area.
14Z temperatures were generally in the 70s with mainly sunny

Current forecast in excellent shape with little adjustment needed.
Surface ridge will drift through the Ohio Valley today maintaining
dry weather and less humid conditions than recent days. Model
soundings show convective temps will likely be approached this
afternoon. Combined with the presence of an 850mb thermal trough
focusing over eastern Indiana...expect the development of a
scattered cu field with greatest coverage over the eastern half of
the forecast area this afternoon. Nudged winds up a bit from
previous forecast as sustained should rise to 10-15mph this
afternoon with briefly higher gusts...especially over northern
portions of central Indiana. Highs in the low and mid 80s look

Zone and grid updates out.


.SHORT TERM.../Tonight through Sunday night/
Issued at 308 AM EDT Fri Aug 18 2017

The main concern for the short term will be on timing and coverage
of convection tonight and Saturday as models agree a sharp upper
trough will pivot southeast over the lower Great Lakes and Ohio
Valley Saturday morning. Increasing moisture, lift and sufficient
instability warrants thunderstorm chances, mainly overnight
through midday Saturday. However, areas northwest of Frankfort,
Crawfordsville and Rockville could see a storm or two late evening
and would not rule out an afternoon storm east of Anderson and
Shelbyville. Best thunderstorm chances look to be from 09z-12z and
north of Indianapolis per the blend.

Broad surface high pressure will return to the area, in the wake of
the upper trough. In addition, moisture will be limited per model rh
time sections. Thus, confidence is good in dry conditions late
Saturday through Sunday night. 850 millibar temperatures from 15 to
18 degrees Celsius combined with the 850 millibar forecasting chart
support normal blend highs in the lower 80s northeast to mid and
upper 80s southwest. Confidence in temperatures to within a couple
of degrees is good. Also, blend lows in lower and mid 60s look good.


.LONG TERM /Monday Through Thursday/...
Issued at 245 AM EDT Fri Aug 18 2017

Ensembles in good agreement during this period. Subtropical ridge
extending through the Tennessee Valley early in the period is
expected to get suppressed as short wave energy digs southeast
through the Great Lakes towards the middle of next week. This will
result in a deep long wave trough over the eastern sections of the
country by the middle of next week.

Ensembles are keying in on Monday night through Wednesday as the
most likely periods for precipitation as the short wave and
associated cold front moves through the local area. Will go with
PoPs for showers and thunderstorms in these periods. Dry conditions
expected in the remainder of the periods.


.AVIATION /Discussion for 181800Z TAF Issuance/...
Issued at 1230 PM EDT Fri Aug 18 2017

Brief restrictions possible in scattered convection early Saturday
morning...otherwise VFR conditions generally expected.

Quiet afternoon in progress with surface ridging over the region.
Diurnal cu field has formed with an 850mb thermal trough drifting
through the forecast area. Expect the cu to linger through the
afternoon with a diminishing trend from the west. Cu will fully
dissipate early this evening. W/NW winds near 10kts with briefly
higher gusts are possible this afternoon.

Clouds will begin to increase later tonight as a weak frontal
boundary drifts into central Indiana ahead of an upper wave.
Overall moisture profiles are not terribly impressive and forcing
aloft is generally lacking. Expect the potential for scattered
convection to briefly impact the terminals from the predawn hours
through Saturday morning. Instability is marginal at best with
KLAF likely to be the only site that may see a stray storm late
tonight. Will carry VCTS here with prevailing showers and a VCSH
mention at the other three terminals.

Model soundings and RH progs are suggestive of the possibility of
MVFR stratocu to move across the region immediately behind the
front for a few hours Saturday morning before more substantial
drying advects into central Indiana by the afternoon. Light and
variable flow tonight and Saturday morning will veer to northwest
by the end of the period.





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