Apr 4, 2018 1300 UTC Day 1 Convective Outlook
Updated: Wed Apr 4 12:52:41 UTC 2018 (20180404 1300Z Day 1 shapefile | 20180404 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180404 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 14,526 1,394,294 Virginia Beach, VA...Salisbury, MD...New Bern, NC...Havelock, NC...Elizabeth City, NC...
MARGINAL 36,064 16,506,407 Philadelphia, PA...Newark, NJ...Norfolk, VA...Chesapeake, VA...Newport News, VA...
Probabilistic Tornado Graphic
20180404 1300 UTC Day 1 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 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
2 % 23,617 2,996,759 Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Newport News, VA...Hampton, VA...
Probabilistic Damaging Wind Graphic
20180404 1300 UTC Day 1 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 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 14,529 1,400,217 Virginia Beach, VA...Salisbury, MD...New Bern, NC...Havelock, NC...Elizabeth City, NC...
5 % 36,112 16,456,999 Philadelphia, PA...Newark, NJ...Norfolk, VA...Chesapeake, VA...Richmond, VA...
Probabilistic Large Hail Graphic
20180404 1300 UTC Day 1 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 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 34,291 4,320,608 Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Newport News, VA...Hampton, VA...
   SPC AC 041252

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0752 AM CDT Wed Apr 04 2018

   Valid 041300Z - 051200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   TIDEWATER REGION FROM EASTERN NORTH CAROLINA TO DELMARVA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM
   EASTERN NORTH CAROLINA TO NEW JERSEY...

   ...SUMMARY...
   Thunderstorms may produce damaging gusts through this afternoon from
   parts of the mid-Atlantic region to eastern North Carolina.

   ...Synopsis...
   Broadly cyclonic flow in mid/upper levels will persist through the
   period, across most of the nation from the Rockies eastward.  The
   main embedded perturbation is a strong shortwave trough, now
   apparent in moisture-channel imagery from eastern Upper MI across
   the western Lower MI/Lake Michigan area to southern IL and AR.  This
   trough is expected to proceed eastward across southern ON and the
   upper Ohio Valley today, reaching southwestern QC, western portions
   of NY/PA, and WV by 00Z, with an embedded/500-mb cyclone over QC. 
   By 12Z, the associated mid/upper-level low will continue
   northeastward and being to merge into the southeastern quadrant of a
   broader, complex cyclonic gyre centered over the Hudson Bay region.

   At the surface, the associated low was analyzed at 11Z near the
   southeastern end of Georgian Bay in ON, and should move east-
   northeastward across southern/eastern QC to become nearly vertically
   stacked with the 500-mb low.  The surface cold front extended across
   western/central PA, southwestern VA, northwestern GA, extreme
   southeastern LA, and deep south TX.  The front is forecast to move
   offshore from the Mid-Atlantic coastline around 18Z, and off the
   Outer Banks of NC by 00Z.

   ...Atlantic Coast States...
   A corridor of scattered thunderstorms is expected to form through
   midday and into the afternoon as the weakly capped BOUNDARY layer
   heats/mixes from the surface.  Activity should gradually become
   better organized as it moves eastward over the marginal-risk and
   slight-risk areas toward the coast, offering a risk of sporadic
   damaging gusts and isolated severe hail.  A brief tornado cannot be
   ruled out.

   Although substantial DCVA-related large-scale lift related to the
   shortwave trough will pass to the north, height falls are forecast,
   and this area will reside beneath the right-entrance region of a
   cyclonically curved, 135-145-kt 250-mb speed max.  Still, midlevel
   lapse rates are expected to remain modest.  Heating-related
   destabilization and adjective airmass recovery each will decrease
   northward and westward from the slight-risk outlook area, while both
   frontal and synoptic/mid-upper lift weaken southward.  This accounts
   for the probabilistic gradation depicted in the accompanying
   severe-risk maps.  Meanwhile, the most favorable boundary layer and
   largest buoyancy are expected to remain offshore, though enough
   return flow may occur close to the coast, from Delmarva to eastern
   NC, to yield favorable boundary-layer thetae for severe in the
   western rim of the best-modified marine air.  Forecast soundings
   over inland parts of this corridor suggest MLCAPE may reach 500-800
   J/kg amidst 45-55 kt effective-shear magnitudes.

   ..Edwards/Broyles.. 04/04/2018

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