SPC AC 140539

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1239 AM CDT Mon Jun 14 2021

   Valid 141200Z - 151200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MID-ATLANTIC...

   ...SUMMARY...
   Thunderstorms associated with damaging wind gusts and hail will be
   possible across parts of the Mid Atlantic this afternoon and
   evening. Marginally severe wind and hail will also be possible in
   parts of the upper Ohio Valley, Carolinas and High Plains.

   ...Mid-Atlantic/Upper Ohio Valley/Carolinas...
   An upper-level trough will move southeastward across the Great Lakes
   region today as a cold front advances southeastward into the central
   Appalachian Mountains. Ahead of the front, a surface low will move
   eastward into the Mid Atlantic as a corridor of maximized low-level
   moisture takes shape across the Atlantic Coastal Plain. Surface
   dewpoints are forecast to be in the mid to upper 60s F, which will
   result in the development of moderate instability during the
   afternoon. Model forecasts suggest that convection will first
   initiate to the northeast of the low during the morning near Lake
   Erie and Lake Ontario. Convective coverage should gradually expand
   along and ahead of the front from western Pennsylvania into central
   New York. This convection is forecast to develop into a cluster of
   thunderstorms, moving southeastward across southeast New York and
   north-central Pennsylvania during the late afternoon and early
   evening. The development of a quasi-linear convective system will be
   possible as this convection moves southeast into parts of the
   Mid-Atlantic, as is suggested by many of the new CAM solutions.

   RAP forecast soundings at 03Z along the path of the projected QLCS
   near Philadelphia have moderate instability, steep low to mid-level
   lapse rates and relatively strong deep-layer shear. MLCAPE is
   forecast to peak near 2000 J/Kg with 0-6 km shear around 50 kt. This
   will likely be favorable for severe storms along the leading edge of
   the QLCS. Supercells and organized multicell line segments will be
   possible from late afternoon to the mid evening as the QLCS moves
   across the Mid-Atlantic. Damaging wind gusts and hail be the primary
   threats.

   The severe threat should be more isolated with southward extent due
   to less forcing and deep-layer shear. In spite of the less favorable
   environment across the Carolinas, a marginal wind damage threat will
   still be possible, mainly due to the moist airmass and very steep
   low-level lapse rates. 

   ...Central and Northern High Plains...
   An upper-level ridge will remain in place across the central Rockies
   and northern High Plains today. Moderate to strong instability is
   again forecast to develop this afternoon from eastern Colorado to
   southeast Montana, along and just to the east of the ridge. In spite
   of a lack of large-scale ascent, convection is expected to initiate
   in the High Plains along the western edge of the stronger
   instability. A few storms could persist and move eastward across the
   High Plains. In spite of the warm air aloft, directional shear and
   steep lapse rates will exist in the low to mid-levels. This could be
   enough for a marginal wind damage and hail threat during the late
   afternoon and early evening.

   ..Broyles/Moore.. 06/14/2021

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