Valid 040100Z – 041200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
Thunderstorms associated with severe wind gusts and large hail will
be possible tonight across parts of Texas with marginally severe
wind gusts and hail possible eastward to the Lower Mississippi
Valley, central Gulf Coast and Florida Panhandle. Marginally severe
wind gusts and hail will also be possible this evening in the parts
of the Mid-Atlantic.
Latest water-vapor imagery shows an upper-level low over northwest
Mexico with a plume of mid-level moisture from northern Mexico
extending northeastward into the southern Plains. At the surface, a
moist airmass is in place from the lower Rio Grande Valley
northeastward into eastern parts of the Texas Hill Country to the
Arklatex. Thunderstorms appear to be developing near a mid-level
vorticity max in west-central Texas on the northwestern edge of weak
instability. As the upper-level low approaches from the west,
large-scale ascent will markedly increase across the Lower Rio
Grande Valley this evening into tonight. In response, thunderstorm
development will expand in coverage.
The RAP is currently analyzing weak instability with MLCAPE of 250
to 500 J/kg across the southern third of Texas, with a band of
maximized instability, located from near Del Rio extending
east-northeastward to the San Antonio and Austin areas. Thunderstorm
development will be most likely along this corridor as large-scale
ascent increases due to the approaching upper-level low. In addition
to the instability, the environment is characterized by strong
deep-layer shear and steep mid-level lapse rates. This is evident on
the Del Rio 00Z sounding with 0-6 km shear of 93 kt and 700-500 mb
lapse rates of 7.6 C/km. In response, convection should be able to
organize with supercells or short-bowing line segments possible. The
potential for supercells with large hail and wind damage will be
greatest late this evening into the early overnight period when
cells will have the best chance to remain discrete. As the brunt of
the large-scale ascent comes out late tonight, line segments
associated with isolated damaging wind gusts will be more likely.
…Lower Mississippi Valley/Central Gulf Coast/Florida
Latest water-vapor imagery shows zonal westerly mid-level flow
across the Southeast with a plume of mid-level moisture extending
from the southern Plains into the Lower Mississippi Valley. At the
surface, a moist airmass is in place from the Lower Mississippi
Valley eastward to the Florida Panhandle. The RAP is analyzing a
pocket of instability in the Lower Mississippi Valley with SBCAPE
near 1000 J/kg. Instability may increase some tonight along the Gulf
Coast due to rising surface dewpoints associated with warm
advection. In response, convective development should increase late
tonight from southern Alabama eastward into the Florida Panhandle
and southern Georgia as is forecast by the HRRR and other hi-res
models. The increasing instability and strongly sheared environment
will likely support damaging wind gusts and hail.
Latest water-vapor imagery shows an upper-level trough moving
eastward across the Great Lakes region with a band of mid-level
moisture from eastern Pennsylvania southward into the Mid-Atlantic.
Thunderstorms are located in this band along and ahead of a
fast-moving cold front. Although the RAP is analyzing weak
instability across the Mid-Atlantic, regional WSR-88D VWPS have
strong deep-layer shear with 0-6 km shear in the 80 to 85 kt range.
This combined with an east-northeastward storm motion near 55 kt
will be enough for a marginal wind-damage threat this evening.