Probability of Watch Issuance...80 percent
SUMMARY...The severe threat is increasing across portions of central
PA into MD. Damaging gusts and perhaps a few tornadoes may accompany
the strongest, longer lived storms. A WW issuance will be needed
within the next couple of hours.
DISCUSSION...A remnant mid-level MCV (evident via water vapor
imagery and 700-500 mb objective analysis fields) is currently
located just west of the OH/PA border and continues to track
eastward towards central PA, and is expected to support more robust
convective initiation in the next few hours. Immediately ahead of
the MCV center lies a highly sheared low-level environment, with
recent PBZ VAD data showing relatively long, curved low-level
hodographs and over 300 m2/s2 of associated 0-1km SRH. At the
moment, buoyancy remains scant across portions of western into
central PA. However, modest breaks in the clouds are contributing to
modest surface heating, with mid 60s F surface temperatures already
noted across central PA, with low 70s F along the PA/MD border. With
surface dewpoints around 60F across several locales, RAP forecast
soundings suggest temperatures need to warm into the lower 70s for
appreciable buoyancy to develop given the presence of relatively
poor (5.5-6.5 C/km) low and mid-level lapse rates.
While buoyancy is expected to initially be marginal (i.e. at or
below 1000 J/kg MLCAPE), localized deep-layer ascent and strong
low-level shear associated with the approaching MCV should support
at least a few strong to severe storms developing early this
afternoon. Damaging gusts and perhaps a few tornadoes will be the
primary concerns, though a brief instance or two of marginally
severe hail cannot be completely ruled out with the longer-lived,
persistent rotating updrafts. A WW issuance will be needed within
the next couple of hours to address the severe threat.