Sep 21, 2018 1630 UTC Day 1 Convective Outlook
Updated: Fri Sep 21 16:26:09 UTC 2018 (20180921 1630Z Day 1 shapefile | 20180921 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180921 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 35,776 8,049,185 Cleveland, OH...Buffalo, NY...Rochester, NY...Akron, OH...Erie, PA...
SLIGHT 43,209 9,653,802 Columbus, OH...Pittsburgh, PA...Cincinnati, OH...Dayton, OH...Syracuse, NY...
MARGINAL 115,043 17,208,593 Detroit, MI...Toledo, OH...Louisville, KY...Lexington-Fayette, KY...Warren, MI...
Probabilistic Tornado Graphic
20180921 1630 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 26,635 4,089,793 Buffalo, NY...Rochester, NY...Erie, PA...Youngstown, OH...Cheektowaga, NY...
2 % 20,981 5,886,387 Cleveland, OH...Pittsburgh, PA...Akron, OH...Syracuse, NY...Parma, OH...
Probabilistic Damaging Wind Graphic
20180921 1630 UTC Day 1 Damaging Wind Probabilities Graphic
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.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
30 % 35,704 8,075,394 Cleveland, OH...Buffalo, NY...Rochester, NY...Akron, OH...Erie, PA...
15 % 43,080 9,592,222 Columbus, OH...Pittsburgh, PA...Cincinnati, OH...Dayton, OH...Syracuse, NY...
5 % 115,957 17,338,308 Detroit, MI...Toledo, OH...Louisville, KY...Lexington-Fayette, KY...Warren, MI...
Probabilistic Large Hail Graphic
20180921 1630 UTC Day 1 Large Hail Probabilities Graphic
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.) Area Pop. 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...

   ...SUMMARY...
   Severe thunderstorm winds and a couple of tornadoes are possible
   across parts of the lower Great Lakes region this afternoon and
   evening.

   ...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.

   ..Thompson/Dean.. 09/21/2018

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z