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acus01 kwns 121259
swody1
Storm Prediction Center ac 121257
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0757 am CDT Wed Jul 12 2017
Valid 121300z - 131200z
..there is a slight risk of severe thunderstorms from the Central
Plains to the Midwest/Great Lakes...
..there is a marginal risk of severe thunderstorms from the
north-Central High plains to the mid-Atlantic/northeast states...
...
Severe thunderstorms are expected today especially from the Great
Lakes region southwestward into the central Great Plains.
..Midwest/Great Lakes...
Multiple clusters of convection are moving southeastward across far
southern WI/far northern Illinois and the Lake Michigan vicinity as of 13z, with
the possibility of strong/locally severe winds this morning with
this relatively fast-moving convection. The downstream boundary
layer will gradually destabilize this afternoon, while recovery and
aggressive destabilization will occur in the wake of the morning
convection, particularly from Iowa into WI/northern Illinois. This will be
as cloud cover scatters and an mesoscale convective system-peripheral elevated mixed-layer
plume advects eastward atop increasingly prevalent lower 70s f
surface dewpoints.
While the 00z/06z NAM depictions of moisture/buoyancy are probably a
bit too aggressive, very strong to extreme buoyancy with upwards of
3000-5000 j/kg MLCAPE seems likely especially from eastern Iowa into
WI/northern Illinois by peak heating. Some uncertainties exist regarding
the specific peak sub-regional corridors of preferred surface-based
redevelopment later today. This is attributable to the early-day
convection/outflow and subtleties regarding forcing-for-ascent
influences, given that the most readily apparent mid-level forcing
will be focused over northern WI/Upper Michigan to the north of the most
robust destabilization.
Initially, one scenario for potentially severe thunderstorms
includes some mesoscale convective vortex-aided redevelopment/intensification by afternoon
as the early-day storms/related mesoscale convective vortex across southern WI spread
east-southeastward into lower Michigan/northern in and Northern Ohio with
damaging winds a possibility.
Farther west, the development of at least widely scattered severe
thunderstorms are likely to be semi-focused mid/late this afternoon
along the east/southeastward-spreading surface low and front
(residual outflow may also be a factor) across WI/Iowa into northern
Illinois. Damaging winds will be the most common severe hazard. Some large
hail will also be possible with any initial supercell modes within
the aforementioned corridor of robust destabilization, with
supercell-supportive long/straight hodographs expected particularly
across WI. While details are uncertain due to early-day
convection/outflow, a tornado or two cannot be ruled out,
particularly near the surface low/effective warm front across
eastern WI and lower mi, given a moderately strong (25-40 kt) belt
of southwesterly winds within the lowest 1-2 km above ground level.
..north-Central High plains to middle MO River Valley...
Widely scattered thunderstorms across the region should largely
diminish this morning as the low-level jet/related warm advection
gradually wanes. Redevelopment is expected later today along the
southwest/northeast-oriented front spanning western/northern Kansas and
southern NE into Iowa/far northern MO, with other terrain/upslope
flow-related development across the Colorado/WY/southern Montana Front Range
and adjacent High Plains. Steep lapse rates, moderate buoyancy and
as much as 30-40 kt of effective shear will support severe storms
capable of severe hail/wind mainly late this afternoon into evening.
.Guyer/Peters.. 07/12/2017
$$
Mesoscale Discussion
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acus11 kwns 121333
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 121333
miz000-ohz000-inz000-ilz000-121530-
Mesoscale discussion 1294
National Weather Service Storm Prediction Center Norman OK
0833 am CDT Wed Jul 12 2017
Areas affected...Chicago...northern Indiana...southwest lower
Michigan...far Northwest Ohio
Concerning...severe potential...watch unlikely
Valid 121333z - 121530z
Probability of watch issuance...20 percent
Summary...isolated strong to locally severe gusts are possible this
morning. There is uncertainty regarding the coverage of damaging
gusts. The current thinking is much of the activity will remain
subsevere as it moves east-southeast across the Michiana region.
Discussion...radar mosaic shows 2 convective lines---the first near
the WI/Illinois border and another over northeast Illinois and Southern Lake
Michigan. The airmass downstream of these thunderstorm lines is
characterized as weakly unstable with 500-1000 j/kg MLCAPE and
surface temperatures ranging from the lower 70s degrees f over
southern Michigan to the upper 70s in north-central in. A 37-kt gust was
measured by the Madison, WI ASOS at 1218z and gusts generally below
30-kt were measured over northeast Illinois with passage of the first
convective line.
Kmkx VAD data is currently sampling a mature rear inflow jet (50-kt
from 3 km agl) over southern WI. Despite the moist/marginally
unstable environment downstream of the mcss, the well organized
character and dynamic processes therein may augment and increase the
threat for damaging winds from an otherwise low risk. Will monitor
convective trends over the next 1-2 hours.
.Smith/grams.. 07/12/2017
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...iwx...GRR...lot...
Latitude...Lon 41378742 41888820 42298669 42418532 42088448 41528440
41268488 41378742
