Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 181028

Area Forecast Discussion
National Weather Service Indianapolis IN
628 AM EDT Fri Aug 18 2017

.UPDATE...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 /Today/...
Issued at 308 AM EDT Fri Aug 18 2017

Cloud trends and temperatures will be the main focus today. Models
in good agreement that a Mississippi Valley high pressure ridge will
settle over the Ohio Valley late today as a cold front moves
southeast of Indiana near daybreak. However, an approaching upper
wave and residual, albeit thinning low level moisture could result
in some fair weather diurnal cu. That said, cu development progs and
rh time sections suggest no worse than partly cloudy skies today.
This should allow for temperatures to reach near normal highs in the
lower and mid 80s per the 850 millibar forecasting chart and model
and mos blend. The warmest temperatures should be over the
southwestern counties per low level thermals.

Confidence is dry conditions and temperatures to within a couple of
degrees is good.


.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 overnigh 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 the 18/12Z TAF Issuance/...
Issued at 628 AM EDT Fri Aug 18 2017

Besides perhaps some brief MVFR fog at the onset, confidence is good
that conditions will be VFR through 09z under the influence of
surface high pressure. Then, could see some showers and possibly
MVFR conditions, mainly at LAF, as an upper trough approaches from
the northwest.

Winds will not be a factor as the remain mostly 6 knots or lower.




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