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Mesoscale Discussion 268
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   Mesoscale Discussion 0268
   NWS Storm Prediction Center Norman OK
   0129 PM CDT Sun Apr 15 2018

   Areas affected...portions of south-central VA...central NC into
   north-central SC

   Concerning...Severe potential...Watch likely 

   Valid 151829Z - 152000Z

   Probability of Watch Issuance...80 percent

   SUMMARY...The severe threat will spread eastward into the NC/VA
   Piedmont vicinity this afternoon and evening. A threat of damaging
   wind and a few tornadoes will ensue as a line of convection across
   western NC/VA continues to track east-northeast across the region. A
   new tornado watch will be needed downstream of WW 52.

   DISCUSSION...Strong heating beneath thin cirrus has allowed
   temperatures to warm into the upper 70s to low 80s across the NC/VA
   Piedmont vicinity this afternoon. This is a bit warmer than forecast
   guidance previously has suggested, resulting in modestly improved
   thermodynamic profiles. Regardless, surface based instability is
   expected to top out around 1000-1500 J/kg at most across the region.
   While midlevel lapse rates will remain lackluster, warmer boundary
   layer temperatures should result in steeper surface to 3km lapse
   rates. 18z Mesoanalysis indicates low level lapse rates have
   increased to around 7 deg C/km. Furthermore, low level kinematics
   should continue to improve as the surface low continues to push
   east-northeast across the central Appalachians. On the whole, this
   will maintain severe threat into the Piedmont vicinity as QLCS
   across western VA/NC/SC continues northeastward. Strong deep layer
   shear with fast storm motion and previously mentioned steepened low
   level lapse rates will support damaging potential. Furthermore,
   backed low level flow and 0-1km SRH greater than 200 m2/s2 will
   support rotation in embedded supercell structures/mesovorticies
   along the line. 

   More recently, showers have developed across the warm sector ahead
   of the eastward advancing line. At this time these showers remain
   rather shallow and weak. While some intensification is possible as
   forcing for ascent increases, severe potential remains uncertain and
   the main focus for severe threat remains the eastward advancing
   line.

   ..Leitman/Guyer.. 04/15/2018

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...AKQ...LWX...RAH...ILM...RNK...CAE...GSP...

   LAT...LON   34467898 34387943 34477985 34588021 34818034 35198045
               35948045 36698050 37128045 37438033 37917979 38107950
               38077905 37957874 37587839 37177831 36387826 34717853
               34467898 

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Page last modified: April 15, 2018
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