SPC AC 050814

   Day 2 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   0314 AM CDT Wed Apr 05 2017

   Valid 061200Z - 071200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THROUGH AT
   LEAST MIDDAY THURSDAY ACROSS PARTS OF EASTERN VIRGINIA INTO
   NORTHEASTERN NORTH CAROLINA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SURROUNDING
   AREAS OF THE MID ATLANTIC COAST REGION...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IMMEDIATELY
   SURROUNDING THE SLIGHT RISK AREA...

   CORRECTED LEAD HEADLINE (FOR DAY OF WEEK)

   ...SUMMARY...
   Organized severe storm development is possible across parts of the
   Mid Atlantic Coast region Thursday, mainly prior to the 2-4 pm EDT
   time frame.  This includes a risk for supercells with potential for
   tornadoes, and perhaps a narrow evolving squall line accompanied by
   potential for damaging surface gusts.

   ...Synopsis...
   An amplification within the westerlies is forecast to continue
   translating across the central into eastern U.S. during this period,
   with large-scale ridging gradually shifting east of the U.S. Rockies
   and Canadian Prairies, and downstream troughing progressing across
   the Appalachians into the Atlantic Seaboard.  The center of a broad
   and deep lower/mid tropospheric cyclone embedded within the
   troughing is still expected to migrate northeastward, near or just
   east of the lower Great Lakes region, with a trailing cold front
   surging eastward and southward, off much of the Atlantic coast,
   including much of the Florida peninsula, and through much of the
   Gulf of Mexico.

   Stable conditions associated with cooling and/or drying in the wake
   of the front will result in low to negligible convective potential
   across much of the nation.  However, prior to the frontal passage,
   models continue to indicate a window of opportunity for organized
   severe storm development across parts of the Mid Atlantic Coast
   region.

   Low probabilities for thunderstorm activity may also accompany a
   couple of short wave perturbations emanating from a strong
   mid-latitude Pacific jet, which may continue to nose inland across
   northern California toward the northern intermountain region.

   ...Mid Atlantic Coast region...
   Models continue to indicate that the exit region of a 90-110+ kt
   cyclonic 500 mb jet streak will nose northeast of the southern
   Appalachians through Mid Atlantic coastal areas early Thursday.  And
   guidance remains suggestive that associated strong forcing for
   ascent will provide support for renewed significant surface
   cyclogenesis to the east of the central Appalachians.  Rapid
   deepening of the surface low may be underway by 12Z Thursday near
   the Blue Ridge, and strengthening southerly low-level flow within
   its warm sector (including up to 50-70+ kt at 850 mb) is expected to
   result in the northward advection of moisture characterized by
   lower/mid 60s surface dew points within a plume across eastern
   Virginia into the vicinity of the low center.  Guidance indicates
   that rapid deepening of the low will continue into midday and
   beyond, with the center possibly tracking across northern Virginia
   and central Maryland before frontal occlusion takes place.

   Given this environment, including thermodynamic profiles initially
   characterized by modestly steep mid-level lapse rates that may
   support CAPE of 500-1000 J/kg, there still appears considerable
   potential for organized severe storm development.  This may include
   discrete supercells capable of producing large hail and tornadoes,
   and perhaps an evolving convective line accompanied by the risk for
   damaging surface gusts, with precipitation loading enhancing the
   downward transfer of higher momentum to the surface.

   Due to the uncertain influence of the cooler/stable marine layer
   near the Chesapeake, greatest confidence in severe weather potential
   still appears focused along/east of the Interstate 95 corridor of
   southeastern Virginia into northeastern North Carolina during the
   late morning through midday hours.  However, given the current
   forecast of the track and rate of deepening of the surface low, this
   threat could develop northward into the Washington D.C and Baltimore
   metro areas, and across the Delmarva peninsula/adjacent southern New
   Jersey, before the front advances offshore by late afternoon.

   ..Kerr.. 04/05/2017

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