Sep 11, 2021 1730 UTC Day 2 Convective Outlook
Updated: Sat Sep 11 17:36:10 UTC 2021 (20210911 1730Z Day 2 shapefile | 20210911 1730Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20210911 1730 UTC Day 2 Outlook Graphic
Day 2 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 25,059 2,987,933 Erie, PA...Binghamton, NY...West Seneca, NY...Ithaca, NY...Jamestown, NY...
MARGINAL 150,563 18,853,653 Detroit, MI...Milwaukee, WI...Aurora, CO...Buffalo, NY...Madison, WI...
Probabilistic Tornado Graphic
20210911 1730 UTC Day 2 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 2 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
2 % 38,941 6,510,222 Worcester, MA...Springfield, MA...Syracuse, NY...Hartford, CT...Erie, PA...
Probabilistic Damaging Wind Graphic
20210911 1730 UTC Day 2 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 2 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 24,850 2,961,150 Erie, PA...Cheektowaga, NY...Binghamton, NY...West Seneca, NY...Ithaca, NY...
5 % 150,729 18,811,496 Milwaukee, WI...Aurora, CO...Buffalo, NY...Madison, WI...Rochester, NY...
Probabilistic Large Hail Graphic
20210911 1730 UTC Day 2 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 2 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 156,363 20,281,786 Milwaukee, WI...Buffalo, NY...Madison, WI...Rochester, NY...Grand Rapids, MI...
   SPC AC 111736

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1236 PM CDT Sat Sep 11 2021

   Valid 121200Z - 131200Z


   Isolated strong to severe storms may occur Sunday from portions of
   the Great Lakes region into the Mid-Atlantic/Northeast, and across
   parts of the northern/central High Plains.

   ...Great Lakes through Northeast...

   A low-amplitude shortwave trough embedded within a belt of stronger
   westerlies will spread east through the Great Lakes during the day
   and into the Northeast States Sunday evening and overnight. At the
   surface a cold front will move southeast into NY and New England
   during the day with the western extension of this boundary likely to
   stall across southern portions of the Great Lakes region. A corridor
   of moderate instability is expected to develop in vicinity of the
   front and in the warm sector. The warm sector will likely remain
   capped mainly across the Great Lakes region as a warm EML spreads
   east. However, elevated storms are likely to develop during the
   morning north of the front across a portion of lower MI. This
   activity will be embedded within strong mid-upper flow. Steep lapse
   rates and moderate instability will support some threat for large
   hail, and some of the storms might also produce a few strong wind
   gusts. This activity may eventually evolve into one or more small
   storm clusters and become surface based as it spreads east into NY,
   where strong unidirectional wind shear may support embedded
   organized structures including bowing segments with damaging wind
   the primary threat from late afternoon into the evening.

   ...Central Plains...

   Much of this region will be located to the north of a weak front in
   a modest low-level upslope flow regime. Low-level moisture,
   characterized by generally mid 50s to low 60s surface dewpoints,
   should spread westward across portions of eastern CO/WY and western
   NE/SD through the day. A subtle shortwave trough with modestly
   enhanced mid-level west-southwesterly flow is forecast to overspread
   this region by Sunday afternoon. Large-scale ascent preceding this
   feature should encourage convective development initially over the
   higher terrain of the central Rockies. As storms spread eastward
   during the afternoon, they will encounter greater low-level
   moisture. Diurnal heating and the presence of modestly steepened
   mid-level lapse rates should support 500-1500 J/kg of MLCAPE by late
   Sunday afternoon. 30-40 kt deep-layer shear should foster storm
   organization as convection moves eastward, with a mix of multicells
   and supercells possible. Various forecast soundings across this area
   show a reasonably well-mixed boundary layer, with potential for
   isolated severe wind gusts with any clusters that can form. Some
   large hail may also occur with supercells. These storms should
   eventually weaken with eastward extent by late Sunday evening as
   convective inhibition increases.

   ..Dial.. 09/11/2021