SPC AC 151900

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 PM CST Sun Nov 15 2020

   Valid 152000Z - 161200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MID-ATLANTIC AND SOUTHERN NEW ENGLAND...

   ...SUMMARY...
   Severe/damaging wind gusts should continue with low-topped showers
   and thunderstorms across parts of the Lower Great Lakes to the
   Northeast and Mid-Atlantic States through early tonight.

   ...Early Afternoon Update...
   A low-topped squall line has produced numerous measured severe wind
   gusts of 60-75+ mph across northern/central OH over the past couple
   of hours. Current expectations are for this line to continue moving
   rapidly east-northeastward across northeastern OH into northwestern
   PA and western NY through the rest of the afternoon. Very strong
   low-level flow (50-70+ kt) noted in various VWPs will remain present
   across this region. The main uncertainty is whether sufficient
   destabilization will occur ahead of the ongoing line given rather
   widespread cloudiness and showers/rain occurring ahead of it. Still,
   there appears to be enough clearing occurring just ahead of the line
   to support robust downward momentum transfer of the very strong flow
   in low levels to the surface. Have therefore adjusted the Slight
   Risk for severe/damaging wind gusts to include areas ahead of the
   low-topped convective line from far eastern OH into northwestern PA
   and western NY. For more information on the near-term severe threat
   across this area, see Mesoscale Discussion 1800 and recently issued
   Severe Thunderstorm Watch 510.

   A small westward expansion has been made to the separate Slight Risk
   extending from parts of the Mid-Atlantic into southern New England
   based on latest observational trends and short-term guidance.
   Earlier thoughts regarding the development of another low-topped
   line capable of producing severe/damaging wind gusts later this
   afternoon/evening across this region remain unchanged.

   ..Gleason.. 11/15/2020

   .PREV DISCUSSION... /ISSUED 1029 AM CST Sun Nov 15 2020/

   ...Lower Great Lakes to Mid-Atlantic/Northeast...
   Scattered thunderstorms are ongoing across southeast Lower MI into
   western OH with a history of widespread strong to isolated severe
   wind gusts. This initial activity may struggle to further intensify
   owing to boundary-layer dew points in the lower 50s within a narrow
   spatial corridor ahead of this convection. It should eventually
   outpace this narrow wedge of surface-based instability as it spreads
   east/north of Lake Erie later this afternoon.

   A more pronounced squall line is expected to develop around 21-23Z
   from central NY to central VA and sweep east-northeast across the
   Northeast and New England coast through early tonight within an
   intense shear/minimally buoyant environment. This squall should
   develop as the robust cold front impinges on low-level moisture
   advecting north from the Carolinas/South Atlantic Coast. Between
   00-03Z, mid 50s boundary-layer dew points should reach as far north
   as eastern PA into southern New England along the track of secondary
   cyclogenesis. While low-level lapse rates will probably remain
   weaker relative to the Lower Great Lakes region, the comparatively
   richer low-level moisture should compensate. It is plausible that
   lightning generation may be confined to areas farther north amid
   scant elevated buoyancy and greater large-scale ascent.
   Nevertheless, the presence of a low-topped squall line amid 50-60 kt
   925-mb winds suggest strong to severe wind gusts are possible even
   in the absence of lightning. As such, this region has been upgraded
   to Slight Risk.

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