Mesoscale Discussions — Strong Thunderstorms & Risk of Tornadoes Continue

Mesoscale Discussion #169

SUMMARY… Thunderstorm activity has tended to generally weaken the past few hours. However, isolated strong to severe thunderstorm development, potentially capable of producing tornadoes, remains possible into this evening, mainly across parts of southeastern Mississippi.

DISCUSSION… Trajectories emanating from surface ridging centered over the southern mid- to subtropical western Atlantic continue to maintain drier near-surface air as far west as southeastern into central Alabama. At the same time, warm mid-level layers persist, with some warming possible during the next few hours, in the wake of one weak mid-level perturbation progressing northeastward toward the Cumberland Plateau, within broader scale anticyclonic flow on the northwestern periphery of the subtropical ridging. With the upstream cold front advancing slowly eastward as well, the pre-frontal plume of moist, potentially unstable boundary-layer air is narrowing.

In conjunction with these trends, both the pre-frontal and frontal thunderstorm development has tended to weaken during the past few hours, and the remnant precipitation associated with the pre-frontal convection is tending to stabilize the boundary-layer ahead of the cold front. With cooling aloft generally lagging well to the west, potential for substantive re-intensification of ongoing convection seems low at the present time. However, wind fields remain at least conditionally supportive of supercells posing a risk for producing tornadoes, and at least pockets of appreciable boundary-layer may persist another couple of hours, particularly around the Hattiesburg, MS area.

Mesoscale Discussion #170

SUMMARY…A strong to locally severe storm or two remains possible in Middle/Eastern Tennessee and possibly northeast Alabama this evening. Increasingly poor thermodynamics should preclude additional watch issuance.

DISCUSSION…Convective trends have generally shown a decrease in storm intensity and organization over the past 1-2 hours. A storm will persistent mid-level rotation has recently dissipated east of Nashville. A couple of stronger storms remain in Middle Tennessee. These storms may maintain some intensity for another hour or two given marginally warm temperatures (around 70 F) in the Chattanooga vicinity. Damaging winds and marginally severe hail are the main threats, though a brief tornado could also occur. Otherwise, precipitation ahead of the stronger activity combined with drier air will limit buoyancy as storms move eastward. While a local extension in time of WW 39 is possible depending on observational trends, additional watch issuance is not expected this evening.

Category: Alabama's Weather, ALL POSTS, Severe Weather