Area Forecast Discussion
Issued by NWS Indianapolis, IN
FXUS63 KIND 300225
Area Forecast Discussion
National Weather Service Indianapolis IN
1025 PM EDT FRI JUL 29 2016
The AVIATION Section has been updated below.
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
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-
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
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
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
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 /Update Discussion for the 30/0000Z TAF Issuance/...
Issued at 1030 PM EDT Fri Jul 29 2016
All sites reporting VFR conditions. Notice that ASOS station KCFJ
and surrounding stations are at 100 percent RH, so it looks like
fog/haze will again develop across parts of central IN. Light winds
will also be a contributing factor in many sites going to MVFR after
Weak surface low between KLAF and KFWA along with a moist and
unstable air mass has been producing scattered TS across central
IN this afternoon/evening. The low should effect the area one more
day before some clearing and a broad mid level trough moves off
Most convection over central IN is between KLAF/KIND and east of a
KIND/KBMG line right now, and this activity is expected to
dissipate after 01Z. Even though there is the scattered TS, VFR
conditions are the rule for now.
Light winds and moist air will once again result in MVFR
conditions early Saturday morning with FG/HZ developing after 08Z
or so. Will return to VFR a few hours after sunrise before
scattered convection redevelops on late Saturday morning/early
afternoon. Activity may be more over eastern areas of IN. Will
take a close look at that for the 06Z TAF issuance.