Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 211506

Area Forecast Discussion
National Weather Service Northern Indiana
1106 AM EDT Mon May 21 2018

Issued at 1106 AM EDT Mon May 21 2018

Showers and thunderstorms will impact the area through tonight
with a threat for strong to severe storms existing mainly south of
Route 24. Drier weather will arrive Tuesday and continue through
the work week with highs climbing to near or above 80.


Issued at 1057 AM EDT Mon May 21 2018

Had to make a bit of a overhaul on morning grids to reflect
majority of precip remaining confined to NW areas through 18Z
before expanding east with upstream development expected.

Main area of rain remained over N Illinois with eastern edge
clipping NW areas. 850 mb warm front has been aiding in sparking
off scattered showers along with with a few lightning strikes now
showing up as nose of elevated instability is arriving. This
feature will continue north with main sfc boundary working north
into central Indiana. CAMs models still try to expand precip
across the area over the next couple of hours, but confidence is
low as to how things will evolve. Regardless, instability will
increase this afternoon and evening across the area, especially SE
areas. Risk of severe still exists and if rain doesn`t expand east
and use some of the instability, could see a slightly increased
risk for severe weather further NE.


.SHORT TERM...(Today and Tonight)
Issued at 301 AM EDT Mon May 21 2018

Convective complex moving northeast across Illinois early this
morning will likely move into the Upper Great Lakes Region around
the Monday morning commute. Recent radar trends have shown
portions of this convection weakening while the storms closest to
the upper shortwave (just north of St. Louis) remain healthy. The
track of this shortwave will bring it over Chicago with time. This
will be close enough to initiate storms across northern Indiana
and southern Michigan. Not expecting too much organization with
this first round of convection as MUCAPE is low (~500 J/kg), but
it will be enough for fair coverage of thunder mention in the wx

As this initial area of convection drifts northward, our
cold front from a few days ago should start to move north as a
warm front. This would allow for a surge of low level moisture to
move into the southern portion of the CWA by midday. This will
also complicate the high temperature forecast as the front is
expected to stall near the Indiana/Michigan state line. North of
the front, temperatures will struggle to reach the 65 degree mark
while locations south of the front could surge into the mid 70s

Our second round of convection heavily relies on our potential to
destabilize after this morning`s convection. Latest CAMs suggest
this will be the case with initiation around peak heating (~17Z-
19Z). Instability may be a bit limited this afternoon with MUCAPE
of 1500 J/kg forecast, but deep layer shear of 40kt to 50kt will
more than be adequate for storms to become organized. There is a
corridor of better instability and deep layer shear of 30kt right
along our southern CWA border which may allow for some discrete
storm development, but the primary storm mode should be multi-
cellular given forecast hodographs. This will result in the
primary threat being strong to damaging wind gusts. The area with
the highest chances is along and south of Highway 24. Forecast
confidence remains low given the influence of the morning
convection on later development.


.LONG TERM...(Tuesday through Sunday)
Issued at 301 AM EDT Mon May 21 2018

Cold front moves into the area on Tuesday. There may be
some lingering convection in the morning. As the front slowly moves
to the southeast, additional develop may be possible around midday.
Strong storms can`t be ruled out with this later convection as
forecast models show decent CAPE of 1000 J/kg, but deep layer
shear is expected to be around 15kt to 20kt. This may be enough
for brief gusty winds. This round of storms should clear the area
from west to east by Tuesday afternoon.

High pressure builds over the Upper Great Lakes region by mid-
week and remains into the weekend. This will bring dry and warmer
weather as daytime highs each day reach into the lower 80s. The
next upper level low drops out of the northern High Plains over
the weekend to bring the next round of rain chances.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
Issued at 649 AM EDT Mon May 21 2018

Areas of MVFR and IFR clouds along with VFR spots continued early
this morning. Most of the lower ceilings were on the north side
of the stationary front. A couple rounds of convection will move
across the area today, keeping the likelihood of lower ceilings
and visibilities.





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