Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk
Area (sq. mi.)
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
SPC AC 211626
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1126 AM CDT Fri Sep 21 2018
Valid 211630Z - 221200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON/EVENING FOR THE LOWER GREAT LAKES AREA...
Severe thunderstorm winds and a couple of tornadoes are possible
across parts of the lower Great Lakes region this afternoon and
...Lower Great Lakes from 21-03z...
A midlevel shortwave trough over the upper Great Lakes will move
quickly eastward over southern ON and QC through tonight, as an
associated surface cyclone moves northeastward and deepens from Lake
Superior. A trailing cold front will progress eastward across the
OH Valley and lower Great Lakes by this evening. Surface heating in
cloud breaks south and west of a surface warm front will allow
destabilization across western NY into western PA/OH, in advance of
the cold front. Thunderstorm development is expected along the cold
front and pre-frontal trough by mid afternoon from OH into
southwestern ON, and perhaps along a weak lake breeze along the east
shore of Lake Erie.
12z regional soundings revealed rather poor lapse rates above 700
mb, though surface temperatures in the 80s with boundary-layer
dewpoints in the 68-72 F range will support MLCAPE of 1000-2000
J/kg. Deep-layer vertical shear will increase with the approach of
the midlevel wave from the Great Lakes, with effective bulk shear
expected to strengthen to 45-55 kt. Though supercells will be
possible with the initial development (mainly in southwestern ON),
largely front-parallel shear vectors and deep-layer flow suggest
that convection will evolve rather quickly into a squall line in the
21-00z time frame. Damaging winds will be the main threat with the
line of storms, given the potential for downward transport of 50-60
kt low-midlevel flow. Along the east edge of the warm sector, there
will be a narrow zone of enhanced low-level shear coincident with
surface-based buoyancy. Based on the expected linear convective
mode, a few embedded circulations and a couple of QLCS tornadoes
will be possible. The severe threat should increase by 20-21z
beginning in central/northeastern OH, then spread east-northeastward
into western PA/NY through this evening. As the storms move east of
the stronger buoyancy and into central NY/PA, weakening is expected
by about 03z.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z