Mesoscale Discussion 0890
NWS Storm Prediction Center Norman OK
1126 AM CDT Wed May 22 2024
Areas affected...Northeast AR...Western and Middle TN...Northwest
MS... Far Southwest KY
Concerning...Severe potential...Watch likely
Valid 221626Z - 221830Z
Probability of Watch Issuance...80 percent
SUMMARY...Increasing thunderstorm coverage is anticipated from
northeast Arkansas into western and middle Tennessee, northwest
Mississippi, and far southwest Kentucky this afternoon. Large hail
and strong gusts are possible, and a watch will likely be needed
soon.
DISCUSSION...Recent radar imagery has shown and increase in deeper
convection across northeast AR, along and ahead of a
southeastward-progressing cold front. Airmass preceding this front
continues to destabilize, with recent surface observations sampling
temperatures in the low 80s and dewpoints in the upper 60s/low 70s.
This warm and moist low-level environment is helping to support
strong buoyancy, despite relatively warm mid-levels and associated
poor lapse rates. Recent mesoanalysis estimates MLCAPE is ranges
from around 2500 J/kg across northeast AR to around 1000 J/kg over
middle TN. Deep layer vertical shear over much of this region is
currently modest, with mesoanalysis estimating effective bulk shear
around 30 to 40 kt. Both buoyancy and vertical shear are forecast to
increase throughout the afternoon, with the increase in buoyancy
driven by continued heating and the increase in shear supported by
increasing mid-level flow.
General expectation is for the currently shallow convection ahead of
the front to deepen over time, with thunderstorm development likely.
Increasing deep layer shear should promote an organized storm mode,
with supercells possible. Large hail up to 1.75" to 2" in diameter
will likely be the primary risk with initial, more cellular storms.
The ongoing activity over northwest AR is expected to continue
eastward, with some interaction between this activity and the more
cellular, pre-frontal development is anticipated. This interaction,
coupled with the steady southeastward progression of the cold front,
will likely promote the transition to a more linear mode. Given the
strengthening westerly flow aloft and ample low-level moisture, the
development of a forward-propagating MCS is possible. Damaging gusts
would be the primary risk with any linear development.
Given all of these factors, a watch will likely be needed soon to
cover the severe potential.
..Mosier/Hart.. 05/22/2024
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OHX...PAH...MEG...LZK...
LAT...LON 35109187 36548997 36878848 36278737 34918840 34178997
34219091 35109187