Day 1 Severe Weather Outlook

Valid 041630Z – 051200Z


Scattered damaging winds and a couple tornadoes are possible through
about 8 PM EDT across parts of the Mid-Atlantic States and New
England. A few tornadoes may occur along the coast of South
Carolina, mainly tonight through early Thursday morning.

…Mid-Atlantic/Northeast States and New England…
At least isolated severe thunderstorms are expected across the
region this afternoon into early/mid-evening. A shortwave trough
centered over Lake Ontario at midday will steadily progress eastward
toward northern New England by early evening. An attendant surface
cold front will reach the Champlain and Hudson Valleys by afternoon
with the trailing portion extending southwest across the central
Appalachians through peak heating.

Ahead of the cold front, mid 60s F surface dew points are prevalent
from Connecticut/Rhode Island southwest into the Mid-Atlantic States
where low 70s F are more common. As a plume of steeper mid-level
lapse rates sampled by the 12Z Pittsburgh sounding spreads east,
MLCAPE of 750-1500 J/kg should develop amid pockets of greater
insolation in the lee of the Appalachians. Consistent with upstream
regional 12Z soundings, strengthening mid-level (700-500 mb)
southwesterly winds will overspread the region, particularly from
Pennsylvania/New Jersey northeastward, with more modest flow aloft
to the southwest.

As storms develop/mature, the setup will support some initial
supercells, and otherwise, multiple clusters/line segments with
embedded supercell structures, particularly from northeast
Pennsylvania/northern New Jersey across southern New England.
Damaging winds will be the most common risk given the strength of
the low/mid-level winds, but isolated marginally severe hail could
also occur. There is also the potential for a couple of tornadoes,
mainly across interior southeast New York and much of southern New
England where the greatest combination of moderate low-level SRH and
buoyancy are expected. The severe risk should gradually wane/move
offshore by the mid-evening hours.

…Coastal Georgia/Carolinas…
Hurricane Dorian will continue slowly north off the Florida/Georgia
coast and approach coastal South Carolina by 12Z Thursday; reference
NHC for the latest forecast details. The overall tornado threat is
expected to remain limited along the Georgia/South Carolina coast
through the afternoon. A greater potential for a few tornadoes
should develop this evening into the overnight across coastal South
Carolina as low-level northeasterly winds substantially strengthen
and hodographs enlarge within the favored northeast quadrant of
Dorian. This may yield a few low-topped supercells within one or
more outer bands that approach the immediate coast of South Carolina
into far southern North Carolina.

…Deep South TX…
TC Fernand will continue west across far northeast Mexico per latest
NHC forecasts. Moderate low-level easterly flow will support
adequate SRH for perhaps a brief tornado and/or isolated
thunderstorm wind damage with scattered convection that persists
from the northwest Gulf across Deep South Texas. This flow should
gradually subside during the evening, limiting the severe storm risk
tonight onward.

…North Dakota/northern Minnesota…
A low-amplitude shortwave trough near the BC/AB/MT border will move
east along the international border towards the Lake of the Woods
region by 12Z Thursday. 700-mb warm advection will strengthen across
northeast North Dakota into northwest Minnesota tonight. A cluster
of elevated storms may evolve southeast from southeast SK/southwest
MB overnight. Thin buoyancy will be a limiting factor, but robust
speed shear within the cloud-bearing layer could support a few
instances of marginally severe hail.

…Central High Plains…
While particularly organized/sustained severe storms are not
currently expected, a very isolated severe storm or two cannot be
ruled across the region late this afternoon and early evening near
the surface boundary/lee trough across the region. Neither
deep-layer shear/buoyancy will be strong, but adequate moisture
coincident with steep lapse rates and 25-30 kt effective shear could
support some stronger updrafts/downdrafts capable of marginally
severe hail and/or wind gusts. Any such risk appears most probable
across northeast Colorado into southeast Wyoming and the southern
Nebraska Panhandle.

…Arizona/Lower Colorado River Valley…
Thunderstorm coverage may remain limited across the lower elevations
of Arizona where a relatively greater reservoir of moisture/buoyancy
will exist (particularly southwest Arizona). However, if/where
storms develop later today, modest easterly steering flow and the
hot/well-mixed nature of the boundary layer could conditionally
support some stronger wind gusts, although the overall organized
severe potential currently appears low.

..Guyer/Nauslar.. 09/04/2019


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.