Mesoscale Discussion 1899
   NWS Storm Prediction Center Norman OK
   0330 PM CST Thu Dec 31 2020

   Areas affected...Parts of southeastern Louisiana into southwestern
   Mississippi

   Concerning...Severe potential...Watch possible 

   Valid 312130Z - 312330Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Increasing discrete thunderstorm development is underway
   across the region.  This could eventually pose increasing potential
   to produce a tornado and/or damaging wind gusts, but it is not yet
   clear that a severe weather watch will be needed, at least prior to
   around 6-7 PM CST.

   DISCUSSION...To the south of a strengthening warm frontal zone,
   surface dew points have increased into mid 60s to near 70F across
   much of southeastern Louisiana, and currently as far north as the
   McComb MS vicinity.  This has contributed to modest boundary-layer
   destabilization, with CAPE now generally on the order of 500+ J/kg. 

   Supported by large-scale ascent associated with lower/mid
   tropospheric warm advection, beneath increasingly difluent mid/upper
   flow, this has contributed to increasing discrete storm development.
   Some of the stronger cells have exhibited rotation, aided by strong
   deep-layer shear beneath 50+ kt southwesterly 500 mb flow.  However,
   southerly low-level flow, though gradually strengthening, remains
   rather modest in strength.  More substantive intensification,
   including to 40+ kt around the 850 mb level, is not forecast to
   develop/shift across the lower Mississippi Valley until closer to
   the 01-03Z time frame.  

   Once this commences, residual boundary-layer instability, coupled
   with enlarging clockwise-curved low-level hodographs, could pose at
   least some increase in potential for supercell structures capable of
   producing tornadoes.  However, until then, though perhaps not
   completely out of the question, this potential seems likely to
   remain relatively low.

   ..Kerr/Grams.. 12/31/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...MOB...JAN...LIX...LCH...

   LAT...LON   30989156 31659075 32149013 30278908 29328951 29419139
               30989156