Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 200848
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
448 AM EDT Tue Jun 20 2017

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

&&

.SYNOPSIS...
Issued at 326 AM EDT Tue Jun 20 2017

Other than a few showers and storms later today and this evening as
a weak upper level wave passes through the area...dry weather is
expected through Thursday as high pressure largely influences
weather across the Ohio Valley. Increasing chances for showers and
thunderstorms are expected late week into the weekend as a cold
front dropping south interacts with a tropical system lifting
north.

&&

.NEAR TERM /Today/...
Issued at 326 AM EDT Tue Jun 20 2017

Scattered rain showers associated with a weak wave aloft continue to
diminish in coverage over southern Indiana and are just about out of
the forecast area as of 0630Z. Skies were clear further north across
the region away from the showers. 07Z temperatures ranged generally
from the upper 50s to lower 60s.

The Ohio Valley remains under the influence of a broad upper trough
that will shift east only slowly today. Yet another wave aloft
within the mean trough...located over western Minnesota early this
morning...will swing southeast through the base of the trough and
across the region by late day.

Much of today will see dry weather and plenty of sunshine as central
Indiana resides under the influence of surface high pressure
centered over the western Tennessee Valley. Cu development should
hold off until the afternoon as convective temps in the upper 70s
are reached. Most of the CAMs suggestive that isolated convection
will not begin impacting parts of the forecast area until late
afternoon...largely 21Z and beyond as the wave aloft approaches.
Weak instability and steep lapse rates through 650-700mb will again
serve as primary drivers in convective development...primarily
focused over the northern Wabash Valley prior to 00Z closer to the
location of the upper wave. Wet bulb zero values between 9 and
10kft support a hail threat once again with stronger cells.

Temps...considering temperature performance on Monday and likelihood
at mostly sunny skies for most into the afternoon...nudged highs up
a degree or two from MAV guidance. Most locations will warm into the
80s today with the lower humidity levels continuing.

&&

.SHORT TERM /Tonight through Thursday Night/...
Issued at 326 AM EDT Tue Jun 20 2017

Forecast challenges focus on precip chances...especially towards the
end of the short term as the forecast area is potentially impacted
by an approaching frontal boundary from the north and a plume of
rich tropical moisture from the south.

Similar to Monday night...CAMs are lingering scattered convection
through the evening as the upper wave rotates through the area and a
weak boundary sags in from the north. Primary focus for any showers
and storms this evening will be north of I-70 closer to the energy
aloft and where the airmass will be more unstable. Presence of a
weak cap further south in closer proximity to the surface high over
western Tennessee should keep dry conditions over southern counties.

Much of the rest of the short term up until Thursday night will see
most of the forecast area remain dry. The aforementioned boundary
will become quasi-stationary over the forecast area on Wednesday
before getting pulled back north Wednesday night as low pressure
kicks out of the northern Plains. While the presence of the boundary
over central Indiana within a weakly unstable airmass could generate
a stray shower or storm...forcing aloft is negligible. Will maintain
a dry forecast at this time. Surface ridging will expand into the
area Wednesday night into Thursday morning maintaining dry weather
along with a distinctly more humid feel to the air as southerly flow
establishes.

The forecast becomes more complicated with lower confidence for much
of Thursday into Thursday night as the region gets slowly squeezed
by a cold front dropping south from the Great Lakes and upper
Midwest...and the arrival of a rich plume of tropical moisture
associated with the disturbance currently over the Gulf of Mexico.
Lack of model consensus...particularly with respect to strength and
track of the tropical system as it makes landfall somewhere in
either Louisiana or Texas on Thursday...makes providing additional
detail into the forecast less than desired at this point. One noted
trend over the last day has been a gradual westward shift to the
landfall which ultimately supports the tropical moisture plume
advecting all the way north into the Ohio Valley by late Thursday.
Precip water values above 2 inches look likely...possibly as high as
2.25 inches by early Friday which would be near the climatological
maximum for late June.

Much of Thursday should remain dry as the surface ridge remains
wedged between the front to the north and the moisture plume form
the south. Eventually though...expect increasing chances for
convection Thursday night as interaction commences between the front
and the tropical system. This interaction is likely to only grow on
Friday which may present additional issues as tropical moisture
continues to advect into the Ohio Valley.

Temps...an overall model blend generally matched low level thermals
for Wednesday and Thursday as highs will return into the upper 80s
to near 90. Lows will recover into the upper 60s by Thursday night
with a progressively muggy feel to the air courtesy of the
increasing surge of tropical moisture from the south.

&&

.LONG TERM /Friday through Monday Night/...

Issued at 333 AM EDT Tue Jun 20 2017

The long term period will start out rather active as a low
pressure system over the Lower Mississippi Valley provides decent
moisture for a cold front moving through central Indiana. As a
result, widespread showers and thunderstorms will be possible on
Friday/Friday night, expecially over the southern portions of the
forecast area. A few showers and thunderstorms cannot be
completely ruled out on Saturday, too, but chances are low. It
won`t be until another upper trough moves through on Sunday that
shower and thunderstorm chances increase again. Further out, as
subsidence strengthens on Sunday night, dry conditions will return
through the end of the extended period. Meanwhile, temperatures
through the period will start out near normal and then fall below
normal through the course of the period.

&&

.AVIATION /Discussion for the 20/09Z TAF Update/...

Issued at 408 AM EDT Tue Jun 20 2017

Update...
No changes.

Previous Discussion...
VFR through the period.

Another weak upper level impulse will skirt north of the area on
Tuesday, which may spark a few showers and perhaps a storm or two.
This is far too uncertain for inclusion at this point, and would
be more likely at LAF than the other sites.

Otherwise, some diurnal cloud cover will be possible mainly
tomorrow. Should see only partial cloud cover at any one time.

Winds will generally be west/northwesterly during the period.
Sustained winds will be as high as 8-12KT, and a few gusts to near
20KT cannot be ruled out tomorrow afternoon, but will only be
included at LAF for now.

No significant obstructions to visibility are expected during the
period.

&&

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

&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....TDUD
AVIATION...NIELD/TDUD



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