Valid 251300Z – 261200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHEAST
LA AND COASTAL MS TODAY INTO TONIGHT…
A couple of tornadoes and isolated damaging gusts may occur today
through tonight from southeast Louisiana into coastal Mississippi.
…Southeast LA to southwest AL through tonight…
A cyclone of semi-tropical origin over the western Gulf of Mexico
will move north-northeastward toward the LA coast by early tonight,
and become part of broader cyclogenesis along a baroclinic zone
across the lower MS Valley, to the east of a closed low over the Red
River Valley of TX/OK. Strengthening low-midlevel winds/shear with
the cyclogenesis and northward advance of the maritime tropical
boundary layer will support a threat for rotating storms spreading
inland gradually today into tonight across southeast LA, southern
MS, and southwestern AL.
A couple of supercells have been observed this morning just off the
MS and southeast LA coasts, though the storms have tended to weaken
after crossing the warm front and encountering the cooler/more
stable boundary layer inland. Northward advance of the warm front
today will result in gradual northward destabilization, starting
across southeast LA this morning and spreading into southeast
MS/southwest AL this afternoon. Local VWPs show sufficient vertical
shear/hodograph curvature for supercells on the immediate cool side
of the warm front, which will support a supercell/tornado threat
today near the coast today as warm sector storms cross the boundary.
Poor lapse rates above 600 mb will limit buoyancy, and there is
some uncertainty regarding how quickly the cool air mass will erode
given widespread clouds and continuing rainfall. Still, expected
northward expansion of the weakly unstable warm sector, the approach
of the Gulf cyclone, and strengthening low-level shear with a 50 kt
low-level jet across MS will support a continued threat for
supercells and perhaps a couple of tornadoes through tonight.