Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 171319

Area Forecast Discussion
National Weather Service Northern Indiana
919 AM EDT Thu Aug 17 2017

Issued at 444 AM EDT Thu Aug 17 2017

Chances for showers and thunderstorms will continue today. There
is a chance for isolated strong to severe thunderstorms later this
afternoon into the evening, especially east of Route 31.
Highs today will be in the lower to middle 80s. Cooler and drier
air will filter in behind this system tonight into Friday. Highs
Friday will be in the middle 70s to around 80. This will followed
by low rain chances on Saturday as an upper level disturbance
tracks through the region.


Issued at 919 AM EDT Thu Aug 17 2017

Showers and now some embedded thunder working into areas west of
I-69 as of 13z. This activity is located within warm/moist
conveyor (30-35 kt LLJ core) in advance of a pre-frontal trough.
Latest HRRR/radar trends track this area of scattered to numerous
showers in moisture-rich airmass east through the remainder of
the forecast area late this morning into the early afternoon.
Slight warming/weak boundary layer destabilization along/east of
I-69 could support an increase in convection/lightning here toward
midday. However, any storms through early afternoon should remain
below severe limits.

The latest SPC outlook has shifted the slight risk a little east
toward and east of the I-69 corridor for the mid-late afternoon
hours. Deep layer shear pushing 30-35 knots and MLCAPE values
possibly to 1000-1500 j/kg (dependent on cloud cover/pcpn)
support this conditional severe threat with poor lapse rates
(warm/moist profile) cover....and potential for
pre-frontal trough to be more active east of the forecast area
definite limiting factors for severe convection.


.SHORT TERM...(Today and Tonight)
Issued at 442 AM EDT Thu Aug 17 2017

Continued conditional severe potential today in association with
strong shortwave trof over western Upper Great Lakes lifting
northeast into Ontario today. Strengthening southwesterly deep layer
flow in advance of attendant cold frontal boundary to bring marked
increase in deep layer shear to about 40 kts along with moderate
instability by afternoon, especially along/east of Route 31. MLCAPE
to increase to around 1000-1500 j/kg with effective low level tap of
lwr/mid 70s surface dewpoints now into Lower Ohio Valley. Primarily
wind risk in short lived bowing segments though low end tornadic
risk in 0-1km 200 m2/s2 helical flow, especially should near surface
flow back in advance of linear convection and/or should discreet
modality develop.


.LONG TERM...(Friday through Wednesday)
Issued at 442 AM EDT Thu Aug 17 2017

Little substantive changes from prior forecast. Secondary wave races
across northern CONUS and digs underneath downstream trof undergoing
filling over northern Great Lakes/eastern Ontario for low chances
convection on Saturday. And another period of decent potential
convection on Dy6 with frontal boundary approach. Feature associated
with initially high belted energy through Canada to sag southeastward
into Upper Great Lakes. Suspect with progressive build of western to
central CONUS ridge in latter part of week to help shunt moisture
south of CWA with temperatures trending seasonably cool.


.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
Issued at 634 AM EDT Thu Aug 17 2017

Warm front has pushed northeast of both TAF sites, taking the
threat of thunder with it, for now. Remnants of storms overnight
was working northeast through eastern Illinois, but been showing
slow weakening trend. Hi res models still want to develop/expand
convection this morning, but trends would seem to suggest a
lesser likihood of this. Will keep VCSH in at both locations after
14Z for now. As for thunder chances this afternoon, best shot
still remains at KFWA, but coverage/duration/timing issues still
warrant holding onto VCTS there with no mention at KSBN which
should be removed from the best potential.


IN...Beach Hazards Statement from 5 PM CDT this afternoon through
     Friday afternoon for INZ003.

MI...Beach Hazards Statement from 6 PM EDT this evening through
     Friday afternoon for MIZ077.

LM...Small Craft Advisory from 6 PM this evening to 5 PM EDT Friday
     for LMZ043-046.



LONG TERM...Murphy

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