Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 180031

Area Forecast Discussion
National Weather Service Northern Indiana
831 PM EDT Sat Jun 17 2017

Issued at 347 PM EDT Sat Jun 17 2017

Warm and humid airmass will remain in place across the area into
Sunday, allowing for favorable conditions for showers and
thunderstorms. Some of the storms may reach severe limits later
this evening into the overnight hours. A cold front will move
through by Sunday night and bring cooler and less humid air to the
area into mid week.


Issued at 828 PM EDT Sat Jun 17 2017

Just minor adjustments to earlier fcst grids this eve. Focus remains
on severe potential overnight. Sct sub-svr storms along wk
boundaries over nwrn portions of the cwa this eve with showers
associated with vort max movg through the east. Upstream, stronger
convection over nwrn IL appears to be organizing into a line. Latest
HRRR/RAP suggests this line will sweep east across our cwa late this
eve and overnight as stronger 0-6km shear pushes east. Moderate
instability around (1500j/kg) fcst across wrn portion of the area as
the line moves in with less instability to the east. So, still
appears svr storms psbl with damaging winds the main threat. Perhaps
a bit lower threat in the east, but given the strong shear moving
in, storms may transition to a well organized line/bow by the
time they reach the east, so not discounting damaging wind threat
there either.


.SHORT TERM...(This Evening through Sunday)
Issued at 347 PM EDT Sat Jun 17 2017

Very difficult forecast with models offering only limited help as
combinations of a handful of boundaries, MCVs and periodic cloud
cover all confusing models.

MCV tracked from N Illinois into Lower Michigan along a warm front
allowing for some showers and storms to form there. Area has been
high and dry through the day as subsidence was holding strong with
little more than some low topped cu near the lake shore area where
differential thermal boundary appears to reside. Boundary appears to
exist from northern Illinois back into SE Iowa where cu development
was picking up and some initiation was under way in a weakly capped
and unstable environment (per 18Z DVN/ILX soundings) with around
2000 j/kg of SBCAPE (lower than many models are depicting). Few
showers now forming NW of Indy working NE on edge of what could be
increasing theta E and weakening cap across the area. Therefore
despite model suggestions of little/no chance for precip, lowered
pops somewhat but still maintained slgt chc /chc pops into early
evening before main show tries to take place to the west.

Leading edge of upper level trough was entering western Iowa
bringing increasing height falls and dynamics which should help
coverage and intensity of storms increase. However, confidence in
impacts to the east remain low as majority of CAMs have shown at
best scattered showers/storms with some not even bringing any precip
in. New 18Z HRRR however may be trying to trend back to more a
broken line entering around/after 4z. General consensus was to drop
any categorical pops in place but hold with likely with a delay in
arrival as well as departure. Storms should enter at least 1000-2000
j/kg of SBCAPE and increasing unidirectional shear to allow some
continued organization if they can maintain themselves. While
somewhat reluctant, did maintain severe wording in the grids with
damaging winds again the main threat. Greatest wind threat appears
to be well SW of the area where better EML will exist. Forecast will
likely undergo further updates as convective trends take shape.
SWOMCD just issued to our immediate west.

Front will be slow to exit on Sunday with pops lingering into the
east areas into the afternoon. Convection may wane but refire again
as heating takes place in at least a moderately unstable airmass.
SPC Day 2 outlook expanded marginal risk back to the west a touch
which appears reasonable.


.LONG TERM...(Sunday Night through Saturday)
Issued at 347 PM EDT Sat Jun 17 2017

Only minor changes to long term with main focus on convective
potential into tonight. Cold front should be generally clear of the
forecast area by late Sunday night with cooler and less humid
conditions settling in for a few days. Weak disturbances will rotate
around the upper low resulting in a few chances for mainly diurnal
showers/few storms given cold air aloft.

Upper level heights will begin to increase by mid week and allow
more of an upward trends in temps. Chances for precip will still
linger along the front as it works north. Highs will climb back to
more normal levels with humidity level increasing. Pattern will
remain somewhat unsettled as wave train continues with said frontal
boundary likely to wobble north and south.


.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 633 PM EDT Sat Jun 17 2017

Wk vort max over central IN causing sct shra lifting into nern IN
which should impact FWA early in the period with potentially
brief heavy ra and mvfr vsby. Shra/TS also has developed along a
a sfc boundary oriented parallel to mean flow from sw MI into nw
IN which will prbly impact SBN early this eve. Again, brief mvfr
conditions psbl as shra move through. Latest HRRR suggests more
robust convection along cdfnt over ern IA will move east across
nrn IN overnight, psbly accompanied by strong/gusty winds and
brief low flight conditions. MVFR strato cu expected in vcnty of
the cdfnt as it moves through Sunday morning, mixing out to vfr
with gusty west winds in the aftn.




LONG TERM...Fisher

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