SPC Mesoscale Discussion: Severe Potential… Watch Possible

SUMMARY…A severe threat may extend downstream of WW 433 from parts of western/central KY into middle TN, far northwest AL, northern and central MS and perhaps far southern AR/northern LA. Trends will be monitored but one or more additional watches may be needed in the next 1-2 hours.

DISCUSSION…The intensity of convection across WW 433 has decreased over the last 30-60 minutes in some area from western TN into eastern AR. Other areas, mainly western KY/southern IL and portions of southern AR, have increased in intensity. In the short term, WFOs PAH, MEG and LZK have addressed the continued strong wind threat will local aerial extensions as needed. Further south and east, the need for additional watch issuance still remains somewhat unclear. There is a well-established cold pool across AR behind the line with a well-defined meso high noted in surface analysis. Ahead of the line, a very warm and strongly unstable downstream airmass is in place across southern AR/northern LA into northern and central MS and portions of western and middle TN. This may allow for a continued sporadic damaging wind threat downstream of WW 433. That being said, effective shear diminishes rapidly with south and eastward extent and is not forecast to increase dramatically this evening, though a 30-40 kt southwesterly low level jet will overspread the region. VWP data from LZK does show evidence of a rear-inflow jet, but it is not overly strong or deep, at around 35-50 kt between .5-1.5 km. Further north, across western KY/southern IL, the line has been intensifying and surging eastward. This is likely being driven by the expansive cold pool across AR/MO as well as stronger deep flow in the vicinity of stronger forcing occurring with a weak shortwave impulse migrating across the mid-MS Valley region. This portion of the line may continue to produce damaging wind gusts and PAH has addressed this by expanding WW 433. A line of storms moved across parts of western/central KY early today, but recent observations show conditions have likely recovered somewhat across western portions of WFO LMK. This may require an additional watch later this evening depending on trends as the line approaches this previously disturbed airmass. Overall trends will be monitored, and at at least portions of the MCD area may need to be addressed with one or more new watches within the next 1-2 hours.

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