Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 190826

Area Forecast Discussion
National Weather Service Indianapolis IN
424 AM EDT Sat Aug 19 2017

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


Issued at 302 AM EDT Sat Aug 19 2017

A weak frontal system will drop southeast of central Indiana today
as an upper wave pivots through from the west. These features will
trigger a few morning thunderstorms over central Indiana. Then, a
broad area of surface high pressure will bring dry weather to the
area through Monday. Strong storms are possible next Tuesday and
Tuesday night as another system swings through. The rest of next
week will be cooler and dry as high pressure builds in in the wake
of the cold front.


.NEAR TERM /Today/...
Issued at 302 AM EDT Sat Aug 19 2017

Main issue for the near term will be timing of showers and
thunderstorms out of the area. Currently, radar was showing an area
of thunderstorms near Attica with light returns not reaching the
ground over our southwestern counties. The convection was occuring
to the north of a warm frontal boundary, over southwestern Indiana
and ahead of an upper trough, over the western Great Lakes and
central Iowa. Model instability progs have at least 500 J/KG CAPE
over central Indiana this morning, so thunder will be mentioned.
High Resolution Rapid Refresh was showing the current and subsequent
convection east of the area prior to 18z. This looks reasonable as
the front is expected to drop southeast and the upper low will be
well into western Ohio by 18z. In addition, deepest moisture will be
southeast of the area.

Based on current radar trends, kept brief likely pops early
northwest tappering to slight chance south central . After 12z, have
chance pops far east and slight chance west. Went dry all counties
after 16z. Confidence in exact timing is moderate.

The rest of the afternoon should see diurnal fair weather cu
decrease in coverage as broad surface high pressure and subsidence
build in.

850 millibar forecasting chart and expected partly cloudy skies
support near normal blend with highs in the lower and mid 80s.
Confidence in temperatures within a couple of degrees is good.


.SHORT TERM /Tonight through Monday night/...
Issued at 302 AM EDT Sat Aug 19 2017

Main focus for the short term will be cloud trends, especially
Monday for the eclipse, as well as timing and coverage of convection
Monday night.

Models in good agreement that zonal flow will be over cenral Indiana
through Monday night overtop a broad dome of high pressure over the
southern states. At the surface, broad high pressure will shift east
of the area on Sunday allowing light return flow and gradually
warming. Upper impulses will interact with residual low level
moisture and could produce scattered diurnal cu and a few mid and
high clouds Sunday per cu development progs and rh time sections.
Although, 850 millibar moisture thins on Monday, rh time sections
hint at increasing mid and high clouds. Still, think partly cloudy
will do both days and the eclipse will still be viewable. Although,
the eclipse could briefly retard temperatures, 21 degree 850
millibar temperatures suggest 90 degrees is possible Monday, mainly
south. It will feel very warm and humid regardless for those
outdoors. Blend temperatures look reasonable and will be accepted.

By Monday night, models hinting at more numerous waves in the zonal
flow along with an approaching frontal system and increased moisture
and instability. Thus, should see a few evening storms northwest
with more coverage overnight and beyond per the blend. Confidence in
exact timing is not great but in the trend is good.


.LONG TERM /Tuesday Through Friday/...
Issued at 232 AM EDT Sat Aug 19 2017

Ensembles are in good agreement with the upcoming weather pattern
during this period. Short wave energy is expected to drop southeast
through the Great Lakes on Tuesday, eventually carving out a long
wave trough over the eastern parts of the country for the rest of
the extended.

Will keep PoPs in the forecast for Tuesday and Tuesday night as the
upper trough and associated cold front move through. In the wake of
this front, it appears a drier and more stable air mass will move
into the area. Will go dry after Tuesday.


.AVIATION /Discussion for the 19/09Z IND TAF Update/...
Issued at 424 AM EDT Sat Aug 18 2017

Pulled VCTS based on lack of lightning.

Previous discussion follows...
Issued at 1152 PM EDT Fri Aug 19 2017

VFR conditions are expected to be the prevailing flight category
throughout the TAF period despite increasing chances for showers
and thunderstorms after Sat 06Z with a frontal boundary. The only
exception could be some MVFR fog formation around dawn at KLAF
dependant on moisture from any showers/storms that do go through
over the next several hours. Meanwhile, winds through the period
will be variable at 4 to 8 kts.




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