Storm Prediction Center Mesoscale Discussion 648

   Mesoscale Discussion 0648
   NWS Storm Prediction Center Norman OK
   1107 AM CDT Mon May 06 2024

   Areas affected...Far northwest Nebraska into western South Dakota
   and far southwest North Dakota

   Concerning...Severe potential...Watch possible 

   Valid 061607Z - 061800Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Thunderstorms developing along a cold front in the
   vicinity of a deepening surface low are expected to continue
   intensifying through the mid-afternoon hours. This activity may
   strengthen to severe limits and require watch issuance by late
   morning/early afternoon.

   DISCUSSION...Over the past hour, strong surface pressure falls (on
   the order of 1-2 mb/hour) have been observed across the western
   Dakotas amid increasing synoptic ascent over the northern High
   Plains. Concurrently, a Pacific cold front is pushing east and
   impinging on a narrow corridor of returning moisture. Consequently,
   weak convection has developed along the front and in the vicinity of
   the surface low. 

   The expectation for the next several hours is for this activity to
   intensify owing to a combination of continued theta-e advection into
   a narrow warm sector (confined to the east by thick low/mid-level
   stratus that is resulting in muted diurnal warming) and steepening
   mid-level lapse rates associated with strong synoptic ascent and
   cooling temperatures aloft. MLCAPE values are forecast to reach
   1500-2000 J/kg by mid-afternoon, which appears to be on track based
   on recent observed trends. Southerly mid/upper-level winds will
   support off-boundary organization of cells that may favor discrete
   to semi-discrete storm modes. Large hail (most likely 1.0 to 1.5
   inches in diameter) and severe gusts will be the predominant hazard,
   but low-level helicity within the warm sector (observed values
   around 150 m2/s2 are noted in the KUDX VWP) combined with ample
   ambient vorticity along the boundary should support a tornado threat
   with more intense cells. The narrow spatial extent of the warm
   sector introduces some uncertainty into the overall coverage of the
   severe threat, but trends will continue to be monitored for the need
   of watch issuance.

   ..Moore/Smith.. 05/06/2024

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

   ATTN...WFO...ABR...BIS...LBF...UNR...CYS...BYZ...

   LAT...LON   42820272 43630338 43870382 44260430 44580466 45050498
               45570517 46000490 46370422 46430302 46240166 46030122
               45370069 44520052 43800051 42790060 42310085 42020150
               42200213 42820272