...Mid-Atlantic and Southeast...
Primary changes this outlook are to add a 45 total severe
probability along with minor northeast and southeast expansion to
the categorical risk areas. Portions of the region, centered on SC
to MD, may warrant an upgrade to a level 4/Moderate Risk in later
outlooks.
A large and deepening upper trough will eject east/northeastward out
of the MS/OH/TN Valleys and across the Appalachians and into the Mid
Atlantic/Northeast on Monday, with an expansive area of strong to
intense wind fields aloft. A deep cyclone will move from Lower MI
into QC, with an occluding cold front arcing southeast across the
northern Appalachians, then south-southwest into the northern Gulf.
This front will clear all but the FL Peninsula by Monday evening.
Ahead of the front, seasonably rich low-level moisture characterized
by 60s surface dew points will spread northward from the eastern
Gulf/western Atlantic. Convection will likely be ongoing at 12Z
Monday, low-topped along the Upper OH Valley to central Appalachian
portion of the front to deep convection in the lee of the southern
Appalachians to eastern FL Panhandle. A diurnal uptick in storm
intensity, including potential for semi-discrete supercells ahead of
the front, should occur from north FL to the Carolina Piedmont.
Further intensification is anticipated midday into the afternoon as
a confined corridor of moderate buoyancy likely develops just ahead
of morning storms.
Enlarged low-level hodograph curvature, in conjunction with
favorable elongation of the mid/upper hodograph, should foster a mix
of broken supercells south with line-embedded supercells in the
reinvigorated QLCS north. With such intense 700-mb flow aptly timed
with the diurnal heating cycle overlying rich low-level moisture,
setup could yield an expansive severe weather day, including strong
tornadoes and significant damaging winds. The degree of
boundary-layer heating, as well as timing of convection that may
outpace the front late D2 into early D3, will play key roles in how
intense severe magnitudes may become. At present, the most likely
corridor for significant/widespread severe appears centered on the
eastern Piedmont to coastal plain from SC to MD around midday into
the afternoon.