Storm Prediction Center Mesoscale Discussion 199

   Mesoscale Discussion 0199
   NWS Storm Prediction Center Norman OK
   1007 AM CDT Sat Mar 15 2025

   Areas affected...Eastern Louisiana and much of Mississippi

   Concerning...Severe potential...Tornado Watch likely 

   Valid 151507Z - 151700Z

   Probability of Watch Issuance...95 percent

   SUMMARY...A Particularly Dangerous Situation Tornado Watch will be
   issued soon. A tornado outbreak with multiple intense to violent
   long-track tornadoes is likely.

   DISCUSSION...Morning observational data continues to support a
   likely tornado outbreak today across parts of eastern Louisiana and
   Mississippi. 12Z RAOBS from LCH and LIX indicate rich low-level
   moisture featuring a mean mixing ratio of 14 to 15 beneath a steep
   EML with mid-level lapse rates of 8 to nearly 9 C/km. This
   thermodynamic profile, combined with broken cloud cover across
   Louisiana and southern Mississippi suggest substantial heating will
   occur and strong instability will be present for much of the day
   today. The EML will play a critical role in the storm mode today.
   Discrete supercells are anticipated given the EML which will
   suppress more widespread convection and also provide enough
   mid-level dry air for potentially multiple well-organized supercells
   in close proximity through the day. In addition, 12Z RAOB data along
   the Gulf Coast is consistent with the data observed the morning of
   historical tornado outbreaks across Mississippi and Alabama.

   Strong shear is already present across Louisiana and Mississippi
   this morning with effective shear 40 to 60 knots at the LIX/LCH/JAN
   12Z RAOBs. However, shear will increase further through the morning
   as mid-level flow strengthens with the mid-level jet streak
   overspreading more of the warm sector and with secondary surface
   cyclogenesis in the mid-Mississippi Valley. Early evidence of this
   secondary low-pressure center has already been observed with a
   sub-995mb surface low analyzed northwest of Little Rock, Arkansas at
   15Z. This surface low will continue to deepen and consolidate
   through the day which will keep flow backed across the warm sector
   and result in further strengthening of the already strong low-level
   jet. By mid-afternoon, a low-level jet of 65 to 70 knots is forecast
   with corresponding 0-1km SRH of 300 to 500 m2/s2. The presence of
   nearly pure streamwise vorticity in the lowest 1km will create an
   environment extremely conducive to the stretching of the ambient
   low-level vorticity.

   Confluence bands across Louisiana this morning likely represent the
   initial supercell initiation zone for the storms of greatest concern
   this afternoon. Multiple bands of supercells are possible. Once
   mature supercells develop in the environment south of the messier
   convection, there should be very little to interrupt their longevity
   through the afternoon.

   Given the aforementioned factors, many discrete supercells are
   expected in an environment which is extremely conducive to tornadic
   activity. Therefore, a tornado outbreak appears imminent with the
   potential for multiple, intense to violent long track tornadoes from
   mid-day through this evening across eastern Louisiana and much of
   Mississippi. A Particularly Dangerous Situation Tornado Watch will
   be issued soon to address this threat.

   ..Bentley/Gleason.. 03/15/2025

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

   ATTN...WFO...BMX...HUN...MOB...MEG...JAN...LIX...LCH...SHV...

   LAT...LON   33289093 33959023 34478950 34728889 34648832 34558813
               33698827 31718846 31238894 30768995 30779104 31009190
               31559220 32039197 32649162 33289093