Mesoscale Discussion 1310
NWS Storm Prediction Center Norman OK
1209 PM CDT Fri Jul 14 2017
Areas affected...Eastern West Virginia...northern Virginia...much of
Maryland...Delaware...southern Pennsylvania...and southwestern New
Concerning...Severe potential...Watch possible
Valid 141709Z - 141915Z
Probability of Watch Issuance...60 percent
SUMMARY...Convective trends are being monitored for a possible
severe thunderstorm watch that may be needed after 18Z or so.
DISCUSSION...A couple of thunderstorm clusters (one over central
Pennsylvania and another newly developing over northern West
Virginia) were gradually increasing in intensity recently. This
increase in coverage/intensity is likely tied to strong surface
heating amidst a weakly capped airmass, with MUCAPE values
approaching 3000 J/kg in some areas. The region resides on the
southern flank of enhanced mid-level flow (40-45 knots over
Pennsylvania), which will likely support at least loosely organized
and forward-propagating convection over the course of the afternoon,
with a primary risk of damaging wind gusts near the strongest
activity especially from northern Virginia eastward to the DelMarVa
Peninsula later in the afternoon.
Farther north into southern Pennsylvania/New Jersey, a nearly
stationary frontal zone was located from near Harrisburg, PA
east-southeastward to near Atlantic City, NJ. Along this zone,
backed surface winds and low-to-mid 70s F dewpoints may contribute
to updraft rotation, especially with any storms that can develop on
the southern flank of ongoing activity in central Pennsylvania. The
orientation of this boundary favors a relatively long residence time
for updrafts that can root near the surface and move/propagate just
to the right of the mean flow vector, and an isolated tornado cannot
be completely ruled out given this regime.
Convective trends are being monitored, and a severe thunderstorm
watch may be needed later this afternoon especially if convective
trends continue as currently observed.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 38417969 38947989 39407968 39927869 40437733 40537656
40387540 40027460 39767450 39297471 38547524 38057593
37877693 37997852 38417969