SPC MD 268


MD 0268 Image

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

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

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


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

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SPC MD 239


MD 0239 Image

Mesoscale Discussion 0239
NWS Storm Prediction Center Norman OK
0206 PM CDT Fri Apr 13 2018

Areas affected...Eastern Kansas...Northwest Missouri...Far Southeast
Nebraska...Southern Iowa

Concerning...Severe potential...Watch likely 

Valid 131906Z - 132130Z

Probability of Watch Issuance...80 percent

SUMMARY...A severe threat is likely to develop across northeast
Kansas, northwest Missouri and southern Iowa over the next couple of
hours. Large hail and wind damage will be the initial threat but a
tornado threat is expected to eventually develop. Weather watch
issuance will likely be needed across the region this afternoon.

DISCUSSION...The latest surface analysis shows a 991 mb low over far
southeast Nebraska with a cold front extending south-southwestward
from the low into northeast and central Kansas. A dryline begins
near the front in eastern Kansas and extends southward into northern
Oklahoma. Thunderstorms are developing along the dryline in
southeast Kansas with other cells initiating to the north of the low
in the Omaha area. This convection is expected to increase in
coverage as the cap weakens over the next hour or so. The storms
should reach northwest Missouri and southwest Iowa by mid afternoon.

Ahead of the storms, a corridor of low-level moisture is analyzed
from far southeast Kansas northward into far northwest Missouri
where surface dewpoints are in the lower to mid 60s F. The RAP is
showing MLCAPE values from eastern Kansas into far southwest Iowa in
the 2000 to 2500 J/kg range. In addition, forecast soundings
steadily increase deep-layer shear along the instability corridor
through late this afternoon. 0-6 km shear should reach the 40 to 50
kt range which will be favorable for supercell development. The
instability, shear and steep mid-level lapse rates will be support
large hail formation with the stronger updrafts. Damaging wind gusts
will also be likely as storm organize. As deep-layer shear and
low-level shear increase later this afternoon, a tornado threat will
also likely develop.

..Broyles/Hart.. 04/13/2018

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


LAT...LON   37869651 38009477 39089392 40369332 41209342 41469430
            41549544 41159619 40559642 39759647 38359705 37869651 

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