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Mesoscale Discussion 167
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   Mesoscale Discussion 0167
   NWS Storm Prediction Center Norman OK
   0746 PM CST Tue Feb 27 2024

   Areas affected...southern Illinois and Indiana into portions of
   northern Kentucky and southwest Ohio

   Concerning...Severe potential...Watch likely 

   Valid 280146Z - 280345Z

   Probability of Watch Issuance...95 percent

   SUMMARY...The severe risk is expected to increase this evening and
   overnight upper-level ascent and a fast-moving cold front intersect
   with the retreating dryline. Bowing segments and supercells will be
   capable of all severe hazards as they spread east along the OH
   Valley. A new Tornado Watch will likely be needed in the next 1-2
   hours.

   DISCUSSION...Over the last hour, surface obs near STL showed the
   dryline retreating westward with a surge in dewpoints to the low 60s
   F. Evening water-vapor and IR imagery showed large-scale ascent
   beginning to impinge on the warm sector across portions of the mid
   MS and lower OH Valleys. Weak convection in the well-mixed warm
   sector to the west has steadily deepened, and should move into more
   robust surface moisture this evening. Additional convection also
   appears likely to develop along the cold front surging southeastward
   across eastern MO later tonight.

   Low 60s F surface dewpoints and ~1000 J/kg of MLCAPE will support
   strong updrafts within the warm sector. Very favorable deep-layer
   shear (50-60 kt) will support a mix of supercells and short bowing
   segments. Damaging gusts and hail appear likely, given the strong
   vertical shear and favorable buoyancy. Rapidly increasing low-level
   shear (evident on area VADs) may support a risk for tornadoes,
   especially with more sustained supercells. A significant tornado
   also cannot be ruled out, given very large effective helicity of
   400-600 m2/s2 and a 50-60 kt 850 mb jet.

   Confidence remains low on the exact timing of convective initiation,
   given that some convective inhibition remains. As ascent begins to
   deepen, most hi-res guidance, and extrapolation of weaker convection
   farther west, suggests new storms should develop in the next 1-2
   hours and quickly become severe. With all severe hazards possible, a
   new Tornado Watch is likely needed in the next couple of hours for
   parts of southern IL/ IN into northern KY and southwestern OH.

   ..Lyons/Edwards.. 02/28/2024

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

   ATTN...WFO...ILN...LMK...IND...PAH...ILX...LSX...

   LAT...LON   36848841 36748893 36778938 37198983 37468988 37978985
               38718946 39188830 40018593 40278485 40188455 39788434
               39268422 38748426 38288439 37958475 37428636 36888832
               36848841 

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