SPC AC 020508

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1208 AM CDT Sun May 02 2021

   Valid 031200Z - 041200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE MONDAY
   THROUGH MONDAY NIGHT ACROSS PARTS OF THE SOUTHERN GREAT PLAINS
   THROUGH THE OZARK PLATEAU AND PORTIONS OF THE LOWER OHIO VALLEY...

   ...SUMMARY...
   Severe thunderstorms are possible, particularly Monday evening into
   the overnight hours, in a corridor from northeastern Oklahoma
   through the Ozark Plateau and portions of the lower Ohio Valley. 
   Some of this activity may pose a risk for large, damaging hail and
   strong wind gusts.

   ...Synopsis...
   Models indicate that a belt of westerlies across the northern
   mid-latitude Pacific may undergo considerable amplification during
   this period.  It appears that this will include a building mid-level
   ridge axis to the west of the British Columbia/Pacific Northwest
   coast, while broader ridging across the southern
   mid-latitude/subtropical eastern Pacific begins to shift inland of
   the California coast and Baja.  As this occurs, initially amplified
   downstream troughing is forecast to progress east-northeastward out
   of the Four Corners states.

   It still appears that a series of smaller-scale impulses may
   gradually emerge from the Southwest, rather than one consolidated
   perturbation, but at least one of these may be fairly prominent. 
   The degree of phasing with mid-level troughing near the central
   Canadian/U.S. border area, within a branch of westerlies to the
   north, remains unclear.  Models continue to vary considerably
   concerning these and associated surface developments, within/beneath
   an otherwise broadly confluent regime across and east of the
   Mississippi Valley.

   In general, it does appear that a surface cold front will continue
   to overtake initially broad surface troughing across the Upper
   Midwest into the southern Great Plains, as cold surface ridging
   noses southward to the lee of the Rockies.  Surface cyclogenesis
   along it will probably remain modest to weak as it advances eastward
   and southeastward, but an influx of seasonably high boundary-layer
   moisture content is expected to precede the front, on seasonably
   moderate to strong southwesterly low-level flow.

   ...Ohio Valley/Ozark Plateau and adjacent southern Great Plains...
   Of particular concern, model output, in general, continues to
   indicate a return of mid 60s to around 70F surface dew points,
   beneath a plume of very steep lower/mid tropospheric lapse rates
   associated with warm and capping elevated mixed-layer air.  This
   will contribute to significant convective instability and sizable
   CAPE on the order of 2000-3000+ K/kg, in the presence favorably
   sheared 30-50+ kt flow in the 850-500 mb layer, supporting
   considerable potential for organized severe convection.

   There still appears a general signal in the latest NCEP SREF, GEFS,
   and ECENS that large-scale forcing for ascent may begin to erode
   mid-level inhibition along the northern periphery of the warmer and
   more strongly capping elevated mixed-layer air, across north
   central/northeastern Oklahoma into southwestern Missouri by late
   Monday afternoon and evening.  A few supercells are possible
   initially, but convection may tend to grow rapidly upscale into one
   or more organizing clusters.  

   Perhaps in response to the approach of the most significant
   mid-level perturbation emerging from the Southwest, further
   consolidation and upscale convective growth appears possible, across
   and east of the Ozark Plateau into lower Ohio Valley overnight. 
   Although continuing spread among the deterministic models precludes
   it at the present time, severe weather probabilities could still be
   increased in later outlooks, within a corridor across parts of
   northeastern Oklahoma, southern Missouri, and northern Arkansas,
   into the lower  Ohio Valley.  Given the environment, strongest
   convection across this region could pose a risk for large,
   destructive hail and strong, damaging wind gusts.

   ..Kerr.. 05/02/2021

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