SPC AC 040558

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Thu May 04 2017

   Valid 051200Z - 061200Z

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

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE INTERIOR PACIFIC NORTHWEST...

   ...SUMMARY...
   A few strong/severe thunderstorms are possible across the
   Mid-Atlantic Friday morning into the afternoon hours. Elsewhere,
   isolated strong to briefly severe storms will be possible through
   the evening across the interior Pacific Northwest.

   ...Synopsis...
   Expansive mid-level low pressure will slowly progress east towards
   the southern Appalachians, before opening and lifting northeast
   towards the Mid-Atlantic as an upstream shortwave trough translates
   south across the upper Great Lakes. An upstream ridge will be
   positioned over the southern/central Rockies and northern High
   Plains, while an amplified trough moves ashore the Pacific Northwest
   coast.

   ...Portions of the Mid-Atlantic...
   Aided by an approximately 50-kt low-level jet, a band of showers and
   thunderstorms will likely be pushing east towards the Mid-Atlantic
   coast Friday morning. Ahead of this convection, southerly flow will
   transport a relatively moist air mass (characterized by surface dew
   points generally in the mid 60s) northward towards Maryland and
   southern Pennsylvania. This warm/moist sector will be narrowing as
   convection spreads east, becoming displaced from stronger
   large-scale ascent to the west. Nonetheless, weak/modest
   surface-based buoyancy will develop northward, such that fairly
   strong low-level and deep-layer shear will likely support a few
   stronger bands of convection, capable of isolated damaging gusts and
   perhaps a brief tornado during the first part of the day.
   Thereafter, it is possible isolated thunderstorms develop farther
   west and northwest closer to a surface trough/front and colder
   mid-level temperatures. These storms would be capable of some small
   hail and gusty winds, but convective overturning, limited heating
   (due to prior precipitation), and drying mid levels make the
   potential for re-development more uncertain.

   ...Portions of the interior Pacific Northwest...
   As mid-level heights fall with the approach of a trough, small-scale
   perturbations embedded in southerly flow and orographic influences
   are expected to foster organizing convection from northern Nevada to
   the northern Rockies Friday. Across western/northern portions of the
   Marginal Risk area, early-day convection and cloud cover may slow
   diurnal heating, reducing the potential for strong/severe storms.
   However, modest heating and sufficient low/mid-level moisture should
   foster MLCAPE upwards of 500-750 J/kg across parts of the region.
   Storms will organize along higher terrain through the day and then
   advance north/northeast within a zone of 35-50 kt of mid-level flow.
   Dry sub-cloud layers and favorable convective-layer momentum will
   potentially yield a few strong to briefly severe storms capable of
   isolated damaging winds.

   ..Picca.. 05/04/2017

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