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July 9-16 Severe Weather/Heavy Rain Potential


Hoosier

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Here's LOT's take

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
858 PM CDT Tue Jul 11 2017

.UPDATE...
858 PM CDT

Evening Update...

Some adjustments to going forecast this evening primarily to
tighten up gradient in pops with focus mainly across far north and
northeast IL, and also bumped overnight mins, Wednesday maxes and
dew point temps a bit.

Surface analysis depicts warm front/old outflow boundary from
central Iowa into central IL this evening. Wind fields are fairly
light as would be expected this time of year however, with an
overall lack of strong convergence along this boundary leading
only to some isolated convection west of the Quad Cities late this
afternoon. It appears the better focus for convection overnight
will focus along the elevated baroclinic zone further north, where
new convection has developed over the past 1-2 hours over
northeastern IA. Convection allowing models (CAMs) are not doing
real well with this activity overall, though the 23-00Z RAP runs
seem to best capture the location of the northeastern IA storms,
and have generally based overnight convective trends on its
depiction, which develops storms northeast into southern WI and
far northern IL, and eventually east-southeast across the lake.
This would mainly affect northern tier of counties and the
northern Chicago suburbs into the early morning hours, so have
generally tightened up the pop gradient depicted in our hourly
gridded forecast to go drier south/central portions of the cwa,
with a tighter gradient to higher pops along the IL/WI border
area. Steep mid-level lapse rates and 40-45 kt effective bulk
shear would support well-organized updrafts which could present a
hail threat from the strongest cores, though the greater concern
will likely be the potential for locally heavy rainfall given the
west/northwest to east/southeast orientation line of storms and
potential for training within near 2" pwat atmosphere. Should be
some northeastward drift of the elevated warm front overnight so
threat may be more of a southern WI issue.


Ratzer
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That MS River cell raising MKX's eyebrows. SPC still hasn't said anything about that group of storms (MD for watch probability wouldn't be amiss...).

Edit (just came out).

National Weather Service Milwaukee/Sullivan WI
800 PM CDT Tue Jul 11 2017

.UPDATE...
The atmosphere is not cooperating. The high resolution guidance,
including the NAM, had been suggesting that we`d see rapid
redevelopment toward midnight along a NW/SE line from about
Baraboo to Milwaukee. This would be along or near the 850mb warm
front lifting through. However, satellite imagery shows an upper
level jet streak has helped to trigger early convection along that
850 boundary over far northeast IA. So, this new convection is
likely to just expand and roll across the area through the evening
hours. We have the moisture, with dewpoints well into the 70s,
effective deep layer shear is pushing 40-50kts. MUCAPE is around
2500J/KG. This is a rapidly changing evolution, remain flexible in
your expectations. Severe storms with large hail and strong winds
are the primary threat, but a few tornadoes are possible,
especially during the evening, west of Madison.
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Adding to the late to the party crowd, I was in North Liberty for most of the day, watched that supercell develop, but after seeing it struggle to the west, and not checking mesoanalysis, I left it(IDIOT!). Only to end up turning around after it dropped the tornado, ended up missing that, but got some fantastic structure as a consolation prize. Still kinda burns missing a tornado I could've easily had if I had only been more observant and checked obs.

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4 minutes ago, Powerball said:

00z NAM does something completely funky.

But the long and short of is it's showing one big nothingburger for majority of the slight risk area tomorrow afternoon and evening, and in fact makes Thursday the "big day."

Yeah I don't see the 12km NAM being right on this, too far north with the boundary and terribly handling the convection to our west.

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Just now, Powerball said:

I've also been getting decent rumbles of thunder for the past 45 minutes, even with the storms being a good 10+ miles away. 

My sent me a small video on FB of some impressive CC (spider lightning) just a bit ago from Eastpointe.

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Walworth County getting pummeled this morning as well. Field, ditch and wetland flooding was prolific. There were channels through the corn fields where stalks were battered to the ground from the rushing water like you see after a high wind event. That was something new for me.


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