Multi-day Severe Weather Threat: 3/23-3/24

quote:

---

...SUMMARY... A severe weather outbreak remains possible across the Lower Mississippi Valley and Mid-South. The most likely time period for strong tornadoes is between 5 pm to Midnight CDT. ...Lower MS Valley, Mid-South, and the TN Valley... Thunderstorms are ongoing along a baroclinic zone from KY southwest to the Edwards Plateau in central TX. Composite outflow has effectively shunted the surface front southeastward this morning. Most CAMs that reasonably handled this convection suggest the recent weakening trend will continue through late morning before renewed storm development occurs towards early afternoon in the OK/TX/AR border vicinity near the primary surface cyclone. This latter activity should drive the broader coverage portion of the severe threat as the surface cyclone deepens and tracks northeast along the baroclinic zone through tonight. Reliable CAM guidance is largely in agreement that an intensifying QLCS will evolve across AR and spread towards the TN Valley through the evening. Here, strengthening low-level winds and enlarging hodographs should compensate for the northern gradient of the surface-based instability plume. This QLCS will likely contain embedded supercell and mesovortex structures supportive of tornadoes (including potential for a few EF2s) and significant damaging wind swaths (up to around 90 mph). Farther south, GOES PW imagery and the 12Z LCH/LIX soundings indicate values have fallen to near an 1 inch along the central Gulf Coast. This dryness pocket above 850 mb will limit buoyancy across the Lower MS Valley until late today. Increasing low-level moisture across the Sabine Valley towards the Ark-La-Miss should eventually yield a plume of moderate MLCAPE around 1500 J/kg by evening. This warm theta-e advection regime should also foster some discrete convection ahead/southeast of the QLCS towards late afternoon into early evening within the resultant MLCAPE gradient. Deep-layer shear profiles will support supercells, a few of which could become long-tracked. Low-level hodographs, while not quite as enlarged as compared to farther north, will favor a threat for strong tornadoes (EF2-3), until warm sector winds becomes increasingly veered from southwest to northeast overnight.

---