Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 291847
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
247 PM EDT FRI JUL 29 2016

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated
below.

&&

.SYNOPSIS...
Issued at 247 PM EDT Fri Jul 29 2016

Low pressure and a remnant frontal boundary across the Ohio Valley
will interact with mid level disturbances to produce periodic
threats for thunderstorms through late Saturday. The front will
briefly drop south of the region late weekend into Monday before
returning back north. This will set the stage for additional daily
chances for storms for much of next week along with a return
of slightly warmer temperatures.

&&

.NEAR TERM /Rest of This Afternoon and Tonight/...
Issued at 247 PM EDT Fri Jul 29 2016

As convective temps have been met over the last few hours...
scattered storms have developed across central Indiana in the warm
and steamy airmass. 18Z temps were in the low and mid 80s.

Convection has developed on schedule this afternoon as airmass has
sufficiently destabilized. Low pressure remains near KLAF with a
boundary extending E/SE into west central Ohio and a second boundary
extending S/SW into southern Illinois. Greatest storm coverage has
been focused in the vicinity of both these boundaries so far but
starting to see additional development in and around remnant
outflows as well.

With the surface low remaining in the region into the evening and an
upper wave approaching from the northwest...expect a continued
uptick in scattered convection through the rest of the afternoon and
early evening. Will focus highest pops over northern counties in
closer proximity to the WNW/ESE aligned boundary extending from the
surface low and where BL shear values will be slightly more enhanced
courtesy of the upper wave passing by. With that being said...40 to
50 pops remain warranted over the entire forecast area through 00-
01Z.

Primary concern with convection will be the heavy rainfall and
localized flash flooding. With PWATs generally above 1.5 inches and
the overall slow and erratic movement of cells...locations that get
underneath storms will get soaked. While mid level lase rates remain
unimpressive...lapse rates up to about 800mb are steeper than that
experienced on Thursday. Thus anticipate a bit better organization
to convection over the next few hours and cannot rule out an
isolated damaging wind gust from stronger cells as elevated cores
collapse. In addition...very weak directional shear present over the
region with the surface low centered near KLAF. This could set up a
favorable scenario for funnel clouds to form briefly similar to what
occurred in central and western Illinois Thursday afternoon. Will
likely highlight this potential in an SPS.

Most convection will diminish after sunset as airmass stabilizes and
the upper wave departs off to the east. Once again...model soundings
do favor potential for patchy fog and low stratus in the predawn
hours.

Temps...model blend will work well for overnight as lows fall into
the upper 60s to near 70 degrees.

&&

.SHORT TERM /Saturday through Monday/...
Issued at 247 PM EDT Fri Jul 29 2016

Forecast challenges focus on precip chances through much of the
short term.

Dirty upper flow pattern will persist through the first half of the
weekend as weak waves continue to track through the Ohio Valley in a
quasi-zonal pattern aloft. Aforementioned surface low will linger
over northern Indiana on Saturday as well. Combined with a moist and
unstable airmass over the region and leftover boundaries from
convection today...expect scattered thunderstorms to develop once
again during the afternoon and evening with greatest coverage once
again over northern counties in closer proximity to the low pressure
and better forcing aloft.

Continued paltry flow through 500mb suggests little to no BL
shear...poor lapse rates...and overall sluggish and disorganized
convective mode and movement. PWATS will remain at or above 1.5
inches on Saturday with heavy rain and localized flooding continuing
as the primary storm threats.

Forcing aloft will shift east of the region Saturday night into
Sunday with weak northerly flow trying to advect slightly drier air
into the forecast area with the old frontal boundary shifting south
of the forecast area. Cannot entirely rule out a few storms on
Sunday with lingering instability...especially over the southern
forecast area closer to the remnant front.

After a relatively quiet night Sunday night as a high pressure ridge
briefly pokes into central Indiana...the front will begin to lift
back north towards the area Monday in response to low pressure
ejecting out into the northern Plains. The frontal boundary will get
close enough to the area to warrant a low precip chance over the
lower Wabash Valley Monday afternoon with drier weather lingering
elsewhere.

Temps...Model consensus continues to look good with highs generally
in the low to mid 80s through the weekend and matches up with low
level thermals.  Expect even warmer temps Monday rising into the mid
and upper 80s. Lows will fall primarily into the mid and upper 60s
over the next few nights.

&&

.LONG TERM /Monday night through next Friday/...
Issued at 143 PM EDT Fri Jul 29 2016

Ensembles in good agreement in building heat ridge northeast into
the Midwest and Ohio Valley towards the middle of next week. Will
keep PoPs going through Tuesday night as warm advection develops
across the area.

There may a relative lull in the convective threat by Wednesday
and Thursday as the air mass may get capped off under the building
ridge. By next Friday, ensembles suggest a rather strong short
wave trough may move through the northern Midwest and northern
Great Lakes. This may drag a front into the local area by then, so
convective threat will increase again at that time.

&&

.AVIATION /Discussion for the 291800Z TAFS/...
Issued at 1235 PM EDT Fri Jul 29 2016

Weak surface low over northeast Illinois and an associated surface
trough near the Illinois state line will result in scattered
convection this afternoon and early evening. Confidence remains
low at this time for direct impacts at the terminals. Brief IFR
visibility restrictions in the heavier cells. CB bases around 020.
Convective threat expected to diminish by 300000Z-300100Z as these
features drift off to the east of the terminals.

Otherwise, lingering high moisture content in the air mass
combined with little wind supports fog development and associated
visibility restrictions after dark. Pattern supports fairly
widespread IFR/LIFR conditions in low clouds and fog after
300600Z.

Outside of convective areas, surface winds less than 7 kts through
this evening.

&&

.IND Watches/Warnings/Advisories...NONE.

&&

$$

SYNOPSIS...RYAN
NEAR TERM...RYAN
SHORT TERM...RYAN
LONG TERM....JAS
AVIATION...JAS



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