Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 191906

Area Forecast Discussion
National Weather Service Northern Indiana
306 PM EDT Wed Jul 19 2017

Issued at 111 PM EDT Wed Jul 19 2017

Hot and humid weather will persist as an upper level ridge builds
across the Mid Mississippi Valley. Furthermore, an impulse will
slide across the region and may set off a shower or thunderstorm
before sunset this afternoon. Thereafter, a weak front along with
weak upper level disturbances will bring a chances for storms
from tonight through Saturday. The first instance of this will
come early Thursday morning. Highs will be near 90 the rest of the
week with lows around 70 to 75. Afternoon heat indices will
mainly be in the 90s the next 4 days.


.SHORT TERM...(This Evening through Thursday)
Issued at 302 PM EDT Wed Jul 19 2017

A few spotty showers/storms cannot be ruled out late this afternoon
into early this evening across nrn IN/far nw OH/sc Lower MI as low
level moisture and MLCAPE continues to increase near a diffuse sfc
trough. Lack of any forcing/flow aloft and weak convergence should
limit coverage/intensity with most locations remaining
dry/warm/humid into tonight.

MCS on target to develop east into the Upper Midwest tonight will
likely hold together east-southeast into the Great Lakes region
later tonight into Thursday morning given ample moisture
return/convergence with a 40-50 kt low level jet...and decent 60-70
kt mid lvl jet associated with seasonably strong shortwave embedded
in west-northwest flow aloft. Latest CAMS solutions favor areas
mainly north of US 30 to be on the southern fringe of this feature,
though a farther south track is possible per propagation vectors
and orientation of main instability axis. The progged wind field
and high moisture content hints a damaging wind threat if any
bowing segments emerge.

The placement of the trailing composite outflow boundary in wake of
the MCS will be the primary driver for temps and renewed convection
Thursday afternoon into Thursday evening. Latest guidance favors
areas along/south of US 30 later in the afternoon/early evening for
scattered convection. Coverage/intensity of any convection may be
limited by subsidence/warming aloft in wake of the above
mentioned shortwave. However, any storms that do break through
could become severe given expectations for moderate boundary layer
destablization and 0-6km bulk shear near 30-35 knots near
outflow. Otherwise, afternoon heat indices may near advisory
criteria (100F) southwest of US 30.


.LONG TERM...(Thursday Night through Wednesday)
Issued at 302 PM EDT Wed Jul 19 2017

A weak low level anticyclone into the Great Lakes will help orient
the frontal boundary more nw to se Thursday night into Friday
morning. The result will be a brief push of drier/less humid air
into into ne IN/nw OH/Lower MI, with areas along/southwest of US 30
in nrn IN not out of the woods for isolated to scattered convection
during this time near boundary/instability axis. Models have come
into a little better agreement in timing of the next convectively
aided shortwave/possible MCS in perturbed westerly flow to move
through the lower Great Lakes Friday night into Saturday. Again,
moisture/instability/flow progs suggest a heavy rain/severe
threat during this time, though confidence in timing/impacts at
this fcst range remains low given low predictability of mesoscale
features in this pattern. Cooler/drier weather is then in store by
early next week as a more pronounced mid level trough through the
Great Lakes/Northeast forces active frontal boundary off to the


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 111 PM EDT Wed Jul 19 2017

An area of high pressure will be slowly pushing east today
allowing the terminals to have light northwesterly winds changing
to more southerly winds by the end of the forecast period. In
addition, little shear, but plenty of instability will allow a few
showers and possibly a thunderstorm or two to fire this afternoon
across the forecast area. Most of these storms are expected to be
non-severe with gusty winds and possibly small hail being the
impacts and may even miss the TAF sites altogether. Next,
especially if the TAF sites do actually receive precipitation
from showers and storms that fire this afternoon, but also with
lighter winds and enough breaks in the clouds, we`ll introduce the
possibility of BR with MVFR VIS. The other thing that would
impact this process would be if the potential convective system
tracks into the region from the northwest earlier than forecast.
The current forecast timing of this system would come into SBN in
the morning and then later in the day for FWA, meaning FWA may be
more affected by VIS restrictions in the morning than SBN. Have
gone with VCSH at SBN for 21z this afternoon as well as for
Thursday morning since the chance for precipitation this afternoon
is low at SBN and storms have a chance to die out before hitting
SBN Thursday morning.




SHORT TERM...Steinwedel
LONG TERM...Steinwedel

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