Mesoscale Discussion 0210
NWS Storm Prediction Center Norman OK
0256 PM CDT Wed Mar 17 2021
Areas affected...Northeast Louisiana...southeast Arkansas and much
of Mississippi.
Concerning...Tornado Watch 32...
Valid 171956Z - 172130Z
The severe weather threat for Tornado Watch 32 continues.
SUMMARY...The tornado threat is expected to increase late this
afternoon/evening.
DISCUSSION...Most of Mississippi is in a relative lull for
convective coverage/intensity with more intense convection to the
east with the stronger low-level jet and to the west near the
surface trough. Within this area, significant clearing has allowed
temperatures to warm into the low 80s with dewpoints in the upper
60s yielding MLCAPE of 1500 to 2000 J/kg per SPC mesoanalysis. This
strong surface heating has led to deep boundary layer mixing (as
evident on the 18Z JAN RAOB) and as a result, surface flow has
veered southwesterly across much of Mississippi which has reduced
low-level directional shear significantly. However, despite this
veered low-level flow, a widespread and potentially intense tornado
threat is still expected late this afternoon/evening as the surface
trough approaches.
Low-level flow in proximity to this surface trough has started to
back across southeast Arkansas and Louisiana. Expect this trend to
continue as the boundary tightens in response to the ejecting upper
trough. Evidence of this ejecting trough and the corresponding
increase to the flow field can be seen on the KLCH VWP where 1km
flow has strengthened by 20 kts (to near 60 knots) within the last
hour. Expect this stronger low-level jet to overspread much of the
warm sector by 22-00Z which should elongate low-level hodographs
substantially.
Expect multiple supercells to develop along this surface boundary in
the next few hours and track northeastward through the late
afternoon and into the evening hours. In response to the
aforementioned instability and strengthening low-level shear, the
12Z HREF shows widespread 4+ STP across much of Mississippi this
afternoon/evening with some areas in excess of 6. This environment
will support the potential for intense/long-track tornadoes through
the late afternoon and evening hours.
..Bentley.. 03/17/2021
...Please see
www.spc.noaa.gov for graphic product...
ATTN...WFO...HUN...MEG...JAN...LIX...LZK...LCH...SHV...