Mesoscale Discussion 0883
   NWS Storm Prediction Center Norman OK
   0807 PM CDT Sat May 27 2017

   Areas affected...Central and eastern OK

   Concerning...Tornado Watch 279...

   Valid 280107Z - 280230Z

   The severe weather threat for Tornado Watch 279 continues.

   SUMMARY...The threat for all severe hazards continues across Tornado
   Watch 279. The coverage of potentially severe thunderstorms is
   expected to increase this evening as a cold front moves into the
   area.

   DISCUSSION...Explosive thunderstorm development has recently
   occurred across portions of northeast and southern OK, with
   additional development underway across central and southwest OK.
   Regional ASOS and OK Mesonet obs, along with radar data, show
   several boundaries across the region, with two notable features of
   interest being a cold front moving southward into central OK, and a
   pre-frontal wind shift near the I-44 corridor, where recent
   development has been noted. 

   In the short term, the primary convective mode is expected to be
   semi-discrete supercells. Extreme instability and sufficient
   effective shear (as noted on the 00Z OUN sounding) will support a
   threat of all convective hazards. Steep tropospheric lapse rates
   will support the potential for very large hail with any discrete
   cell. The tornado threat will be limited to some extent by
   relatively weak low-level flow, though as the low-level jet
   increases this evening from south-central into northeast OK, the
   tornado threat will increase with any remaining discrete cells. The
   cells currently developing across Lincoln into Creek County and also
   Stephens County may also have some increased tornado potential as
   they interact with the pre-frontal boundary. 

   Later this evening, an increase in convective coverage is expected
   along the cold front as it advances southeastward. A transition to
   more of a linear or QLCS mode is expected as that occurs, though all
   severe hazards will continue to be possible given the magnitude of
   instability and shear across the region.

   ..Dean.. 05/28/2017

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

   ATTN...WFO...TSA...OUN...

   LAT...LON   34389909 35339842 36469674 36859582 36929499 36539472
               35859493 34659584 34199620 33939656 33979701 34019739
               34169781 34219822 34389909