SPC AC 030545

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1245 AM CDT Thu May 03 2018

   Valid 031200Z - 041200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON AND EVENING ACROSS THE LOWER MISSOURI/MIDDLE MISSISSIPPI
   VALLEY REGION...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE LOWER GREAT LAKES AND ALLEGHENY PLATEAU INTO SOUTHERN NEW
   ENGLAND...

   ...SUMMARY...
   Severe thunderstorms are expected to impact the lower Missouri and
   middle Mississippi Valley region late this afternoon and evening,
   with additional severe thunderstorms possible in a corridor across
   parts of the lower Great Lakes region into southern New England, as
   well across parts of the southern Plains by late tonight.

   ...Synopsis...
   Fairly strong mid/upper ridging within the subtropical and
   mid-latitude westerlies appears likely to persist across much of the
   southeastern U.S., while ridging also builds inland of the Pacific
   coast through much of the Intermountain West.  In between, troughing
   may linger across portions of the Four Corner states, but the most
   prominent impulse emerging from it appears likely to accelerate east
   northeast of the Colorado Rockies today.  As it does, it likely will
   be accompanied by at least a modest surface frontal wave/low across
   the central Plains through lower Missouri Valley region by early
   this evening.  More substantive deepening of the low may commence
   late tonight across the Great Lakes region, when models suggest
   increased phasing of its associated upper impulse with another short
   wave impulse digging east southeast of the Canadian Prairies.

   Although a plume of very warm elevated mixed layer air emanating
   from the Mexican Plateau region is in the process of becoming at
   least somewhat suppressed, mid-level lapse rates may remain modestly
   steep across the central/southern Plains into Mississippi Valley
   region.  Coupled with continued low-level moistening on southerly
   return flow around the Southeastern ridge, east of the southern
   Plains dryline, and southeast of the frontal zone extending across
   the central Plains through the Great Lakes region into portions of
   the Northeast, sufficient destabilization likely will occur today to
   support areas of strong/severe thunderstorm development.

   ...Plains into lower Missouri/mid Mississippi Valley...
   Remnant convection/cloud cover probably will at least slow warm
   sector boundary layer destabilization early today into this
   afternoon.  However, beneath a developing mid-level dry slot
   associated with the short wave impulse and accompanying 70-90 kt 500
   mb jet, destabilization preceding stronger mid-level forcing for
   ascent seems likely to provide the focus for the most certain severe
   weather risk today.  By late afternoon, this is expected across
   parts of the lower central Plains into lower Missouri Valley, where
   the environment may become conducive to discrete supercells capable
   of producing large hail and a few tornadoes.  It is possible that
   this activity could grow upscale into an organizing convective
   system with increasing potential for damaging wind gusts near the
   Missouri/Iowa border vicinity through this evening, before weakening
   in waning instability as it approaches the Great Lakes region
   tonight.

   Southward through the southern Plains, severe thunderstorm potential
   during the peak late afternoon and evening hours may be more
   isolated in the presence of weak forcing for ascent.  However, it is
   possible that strengthening ascent ahead of remnant upper troughing
   may contribute to increasing thunderstorm activity with at least
   some severe weather potential across parts of the Edwards Plateau
   into central Texas late this evening into the overnight hours.

   ...Great Lakes adjacent Allegheny Plateau into New England...
   Peak boundary layer destabilization along and just south of the
   quasi-stationary surface frontal zone may be fairly modest
   (generally on the order of 500-1000 J/kg) today.  However, a belt of
   30-50 kt lower/mid tropospheric flow with a number of small-scale
   perturbations, well in advance of the main impulse emerging from the
   Great Basin, may enhance afternoon and evening thunderstorm
   development.  Some of this may become capable of producing damaging
   wind gusts.

   ..Kerr/Leitman/Bentley.. 05/03/2018

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