Area Forecast Discussion
Issued by NWS Indianapolis, IN
FXUS63 KIND 310400
Area Forecast Discussion
National Weather Service Indianapolis IN
1200 AM EDT SUN JUL 31 2016
The AVIATION Section has been updated below.
Issued at 333 PM EDT Sat Jul 30 2016
After scattered storms through this evening...low pressure will
track away from the area this evening as a remnant boundary drops
south into the Tennessee Valley. This will bring drier weather to
central Indiana through early Monday. The front will return north
into the Ohio Valley early next week as a upper ridge expands
towards the area. 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 945 PM EDT Sat Jul 30 2016
Nearly all of the convection has dissipated across central Indiana
with loss of heating. The exception is the far northwest forecast
area where isolated showers continue. Heavier showers are just north
of this area.
A weak surface trough across the far northern forecast area is
helping keep these showers going, but they too should dissipate
within the next couple of hours as instability continues to
Thus ended PoPs now across the southern 2/3 of the area but kept 20
PoPs north third until midnight.
Otherwise forecast remains in good shape. Made some tweaks to sky
cover and min temperatures but no significant changes made.
Previous discussion follows...
Isolated to scattered convection had developed this afternoon on the
northern fringes of the forecast area and across far southern
Indiana in areas of better moisture pooling. Drier air and
subsidence noted on the water vapor imagery earlier today has
manifested over much of the forecast area with precip water values
down at 1.2 to 1.4 inches and dewpoints into the mid and upper 60s.
19Z temps ranged from the upper 70s to mid 80s most locations.
Surface low has moved east into northwest Ohio with better forcing
aloft associated with the upper wave aligned to our northeast as
well. Appears to be a lingering boundary extending westward across
north central Indiana and Illinois and will likely see convective
development in the vicinity of this boundary over the next few
hours. Elsewhere across the forecast area though...presence of the
drier air and consequently lower instability levels are limiting
convective development. In the absence of better moisture and
instability..any showers or storms will be reliant on old outflows
from Friday or whatever boundaries kick out from convection forming
across northern counties. Ended up bumping pops down a bit further
from earlier with these thoughts in mind. Highest pops at 30-40
across the northeast half of the forecast area with lower pops for
mainly isolated convection over the rest of the forecast area. As
has occurred the last few days...expect convection to diminish
around or shortly after sunset.
Rest of the night will be quiet with the potential once again for
low stratus and patchy fog to form in the predawn hours as the
airmass remains stagnant. The slightly drier airmass however may
serve to limit the coverage of the fog and how low visibilities go.
Temps...model blends have worked well for overnight lows the last
several days and see no reason to deviate for tonight. Most everyone
in the forecast area will fall into the 60s and it should feel
more comfortable with the slightly lower dewpoints present.
.SHORT TERM /Sunday through Tuesday/...
Issued at 333 PM EDT Sat Jul 30 2016
Forecast challenges are yet again going to focus on convective
potential over central Indiana...particularly for Monday through
The pesky remnant boundary that has lingered over the area the last
few days will finally be pushed south of the forecast area on Sunday
as a surface ridge passes through the Great Lakes and drier air
spreads into central Indiana. Considering the difficulty in
generating convection over the forecast area this afternoon and the
airmass will be even less favorable for storms on Sunday as a cap
develops...feel comfortable in pulling pops entirely through the
day. Not out of the question to get a rogue shower but the chances
are so low it is not worth mentioning in the forecast at this time.
Developing upper ridging over the central Plains by late weekend
will promote a return to northwest flow aloft into the Ohio Valley
for early next week...and this will set the stage for a return to
more active weather in the form of a series of convective clusters
as the old frontal boundary is drawn back north into the area.
Initially Sunday night...expect convection to develop over the
Missouri Valley in closer proximity to the low level jet and track
E/SE along the instability gradient into central and southern
Illinois. These storms conceivably may clip the lower Wabash Valley
on Monday but overall anticipate the greater impacts from the first
convective cluster will remain to our southwest. Have thrown out the
12km NAM as an outlier as it is essentially the only model tracking
the convective cluster much further north and east of other guidance
and directly across the forecast area on Monday.
Flow will veer around to southerly Monday night and Tuesday as the
boundary remnants shift north. This will allow much more humid air
to advect back into the region. Hints are there for greater impacts
from convective clusters Tuesday into Tuesday night as the ridge
expands...placing central Indiana on the favorable flank for storm
tracks. Something to monitor going forward.
Temps...used a model blend for highs Sunday and Tuesday and trended
towards much warmer MAVMOS for Monday. Highs will gradually warm
back up into the mid and upper 80s by Tuesday. Lows will largely
remain in the 60s.
.LONG TERM /Tuesday night through next Saturday/...
Issued at 146 PM EDT Sat Jul 30 2016
Ensembles in good agreement in expanding heat ridge northeast into
the Midwest and Ohio Valley by the middle of next week. Appears
the local area will be close to being capped off by that time,
which may result in relative lull in the convective threat.
By late next week, a rather strong short wave trough may push
through the northern Great Lakes. This may serve to bring a front
into the area, along with an increased threat for convection by
next Friday and Saturday.
.AVIATION /Discussion for 31/0600Z TAF Issuance/...
Issued at 1200 AM EDT SUN Jul 31 2016
Weak area of low pressure will be off into northern areas of PA this
morning allowing high oressure to come down from WI. Light winds
will allow some areas of fog dropping conditions down to near MVFR
in most areas, but could see some brief IFR visibilities between 10Z
and 12Z. Should return to VFR by afternoon with some scattered
clouds as mean RH values come down and extend eastward across