The Storm Prediction Center kicked out a Mesoscale Discussion regarding the severe weather threat this afternoon and evening for parts of Louisiana and Mississippi. They are unimpressed in terms of a widespread severe weather event, but are concerned about isolated severe storms.
The threat starts now and will last through about 10p tonight. And perhaps linger through the overnight hours.
As discussed this morning in the full forecast, widespread severe weather in a setup like this isn’t very common. But a few storms may be able to ride little boundaries between places with all of the right ingredients and strengthen past severe limits. We don’t expect a line of storms to develop, but instead individual supercell thunderstorms.
And as a lot of you know from hearing me talk about this over the years, the supercells are the ones (as the name implies) that tend to be the beefy big brother of thunderstorms. These guys tend to produce the heaviest rain, gustiest wind and the stronger tornadoes.
And while it still looks like we can’t rule out a brief and weak tornado, today, the potential for something stronger than an EF2 is very, very, very low. Not zero, but pretty low.
From the SPC:
SUMMARY…
An isolated severe threat may develop in the next couple of hours across portions of eastern Louisiana into southern Mississippi. The strongest, longest lasting storms may produce a couple of damaging wind gusts/marginally severe hail stones or a brief tornado. A WW issuance is not currently expected given the sparse nature of the severe threat.
DISCUSSION…
Warm-air advection continues to transport moisture north from the Gulf of Mexico into the TN Valley in advance of a 999 mb surface low along the KS/MO border. This moist low-level airmass
remains modestly capped, though continued warming and moistening beneath the inversion layer has been gradually eroding the cap across eastern LA into southern MS per 18Z mesoanalysis. In
addition, visible satellite depicts a gravity wave propagating across central MS/LA, which may act as an additional source of lift.
Finally, both 12Z NAM and 19Z RAP forecast soundings show cooling of
the inversion layer in the 20-22Z time frame. As such, convective initiation appears likely within the next couple of hours despite overall weak synoptic forcing for ascent.
925-850 mb flow is expected to either remain modest or even weaken further as the surface low weakens while tracking northeast. Nonetheless, modest veering and strengthening within the lowest 3 km supports 150-300 m2/s2 0-3km SRH per DGX/LIX VWPs sampled within the last half hour. Given semi-discrete/discrete storms modes, 30-40 kts of effective bulk shear, and 1000-2000 J/kg MLCAPE (driven by 7 C/km mid-level lapse rates atop near 70 F dewpoints), transient supercells will likely be the dominant storm mode.
Any stronger, more sustained supercell structure that can materialize may produce damaging gusts, marginally severe hail, or perhaps a brief tornado (as 150-200 m2/s2 SRH sampled in the VWPs resides in the 0-1 km layer). However, given the isolated nature of the severe threat, a WW issuance is not currently anticipated.
