Valid 272000Z – 281200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
The severe threat has diminished across the Mid-Atlantic coast and
eastern North Carolina and severe storms are not expected the
remainder of the forecast period.
The effective cold front has moved offshore much of the Mid-Atlantic
coast from near NYC southward toward Chesapeake Bay. From there, the
boundary stretches across eastern NC toward coastal areas of SC. Low
level flow has veered ahead of the boundary and upper forcing for
ascent has shifted well northeast of the region. With a lack of
convergence along the front, convection has mainly been limited to
shower activity with little vertical growth noted in 5 and 7 km
CAPPI over the last hour, save for one cell over Hyde County NC.
This cell could become strong as it moves offshore over the next
hour. Otherwise, little additional development is expected. In the
absence of stronger low level convergence/upper forcing, overall
severe threat appears very limited in both space and time, and the
Marginal risk has been removed.
.PREV DISCUSSION… /ISSUED 1125 AM CDT Sun Oct 27 2019/
…Coastal Mid-Atlantic States to eastern NC…
A shortwave trough across southern ON will progress east across the
St. Lawrence Valley and northern New England through tonight.
Near-neutral mid-level height change is progged this afternoon in
the warm sector ahead of a trailing cold front that will push east
across the Piedmont and Coastal Plain, with heights rising by early
evening. Low-level wind fields will weaken and veer from south to
the north as the occluded surface cyclone over Georgian Bay
12Z NAM suggests low-level convergence along and ahead the front in
NC will be weak with a distinct lack of QPF by late afternoon.
Recent HRRR runs still suggest potential for scattered storm
development across eastern NC, although this is the most aggressive
scenario of the 12Z HREF members. This region will have the greatest
opportunity to destabilize given some cloud breaks amid low 70s
boundary-layer dewpoints. Decreasing hodograph curvature and the
mixed signal for storm sustenance in this region suggest the overall
threat for damaging winds will probably remain isolated.
Farther north in the Delmarva, a pre-frontal convective band
persists with a mix of low-topped showers and embedded deeper cores
producing sporadic lightning. The opportunity for intensification
will be short-lived given poor mid-level lapse rates and modest
boundary-layer heating ahead of it. Still with strong low-level
shear for the next few hours, a risk for a brief tornado and locally
damaging winds may yet be realized, with these threats expected to
cease by late afternoon.