Severe Weather Discussion - Thursday 4/18 930 AM

Here's the latest day 1 convective outlook from the SPC. It features a large moderate risk, that stretches from the northern half of Mississippi into the southern parts of Lower Michigan. This large risk is primarily for damaging winds, some significant; however, there's also a relatively high threat (10%) of tornadoes inside this moderate risk.

Surface observations show a frontal boundary across east-central Texas, west of Texarkana, stretching NNE into western Arkansas up to just east of St. Louis, then stretching NE to the IL/IN border. Ahead of this feature, warm, moist southerly to south-southeasterly flow is prevalent. Locally here in north MS, temperatures are already into the lower 70s with dew point temperatures ranging from 61-64 F. Visible satellite imagery shows many breaks in the clouds, and I expect temperatures to soar into at least the low 80s, if not higher. Dew point temperatures may hover right where they are now, but I expect an increase in those values toward sunset. Also interesting to note, you can see low level clouds streaming in from the southwest on the visible imagery, while mid to high level clouds are streaming in from the west...very neat, yet slightly troubling...

Already in Arkansas, the SPC just issued a tornado watch across north-central Arkansas into southeast MO due to storms that could potentially be increase in coverage and intensity. Shallow, pre-frontal convection has already fired up across south-central AR and just west of Little Rock. As the boundary layer continues heating throughout the day, it is expected these storms will continue to deepen and acquire severe thresholds over the next several hours. SPC mesoanalysis forecasts SBCAPE values exceeding 2000 J/KG within the next 6 hours in advance of these storms over east Arkansas down into the MS Delta.

The wind profile will remain highly supportive of organized convection throughout the day today, particularly the upper-jet structure. Very diffluent patterns are noted at 300mb, which favors enhanced uplift at the surface. Also, the area over central AR, where the shallow convection has already developed, looks to continue to be in a region of PVA at the mid-levels as well...meaning continued uplift potential.

These atmospheric characteristics should carry over into the northern half of MS later this evening. CAPE will likely not be as high as what is being forecasted across the NW Delta into east Arkansas, however it will be sufficient to maintain a potentially intense squall line that should have already coalesced. As the low-level jet increase nocturnally later this evening, the wind/tornado threat may pulse up once more during the late evening across north MS into southern Middle TN. Any supercellular structure either ahead of the line or that can establish itself within a squall line will have enhanced tornado potential.

Please remain weather alert today...
IW