Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 300621
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
220 AM EDT SAT JUL 30 2016

.UPDATE...
The LONG TERM Section has 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 Tonight/...
Issued at 948 PM EDT Fri Jul 29 2016

Convection continues its diurnal downward trend this evening.
However, cannot completely rule out more isolated convection
developing tonight with weak upper energy and plenty of surface
boundaries around. Thus have lowered PoPs to slight chance and
will continue the isolated thunderstorm forecast overnight.

Otherwise forecast is in good shape. Still expect patchy fog to
form, especially in areas where rain fell today. Temperatures look
good.

Previous discussion follows...

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 /Tuesday through next Friday/...
Issued at 220 AM EDT Sat Jul 30 2016

Operational models and ensembles in decent agreement that upper
waves will drop southeast over the area Tuesday into Wednesday as a
warm front gradually lifts northeast over the Wabash Valley and the
rest of central Indiana late Wednesday and Wednesday night. These
features will interact with a warm and unstable airmass and allow
for scattered thunderstorms with the best chances Tuesday night.
After that, the upper dome of high pressure over the middle of the
nation will build northeast over the Ohio Valley and lower Great
Lakes and result in warmer temperatures and only small thunderstorm
chances Wednesday night through Thursday night. Finally, an upper
Canadian low will force a cold front to drop southeast over the area
early next weekend. This will bring another decent shot of
thunderstorms in starting Friday. Regional blend looks to have a
good handle on temperature trends as well as pops. Could see 90
degrees again in the south by Thursday.

&&

.AVIATION /Discussion for the 30/0600Z TAF Issuance/...

Issued at 1205 AM EDT Sat Jul 30 2016

An area of low pressure over the Ohio Valley once again will combine
with moist conditions overnight to produce MVFR conditions towards
dawn. Currently, all sites are VFR, but with generally light winds
and dew points in the upper 60s to around 70s looks like there will
be some fog at many of the sites.

Fog will dissipate 12Z-13Z across many areas and with the low
pressure still present, a chance for scattered TS will be around
after 17Z into the early evening hours.  Models are indicating a bit
of a dry slot from KHUF - KBMG towars later afternoon, so TS chance
may diminish before evening in these areas.

&&

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

$$

SYNOPSIS...RYAN
NEAR TERM...RYAN/50
SHORT TERM...RYAN
LONG TERM....MK
AVIATION...DWM



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