SPC AC 051729

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1229 PM CDT Fri Jun 05 2020

   Valid 061200Z - 071200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE SATURDAY
   AFTERNOON AND EVENING ACROSS PARTS OF NORTHWESTERN
   NEBRASKA...WESTERN AND CENTRAL SOUTH DAKOTA AND ADJACENT PORTIONS OF
   SOUTHEASTERN MONTANA AND SOUTHWESTERN NORTH DAKOTA...

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the northern
   plains Saturday into Saturday night.  This may include an evolving
   cluster of storms across parts of western South Dakota and Nebraska,
   which could pose a risk for strong wind gusts and severe hail while
   spreading into portions of the middle Missouri Valley Saturday
   evening.

   ...Synopsis...
   Models continue to indicate considerable amplification within the
   stronger mid-latitude westerlies during this period.  A broad and
   deep mid-level low and associated troughing appears likely to dig
   across the Pacific coast through much of the Intermountain West by
   late Saturday night.  As this occurs, downstream ridging is expected
   to build along an axis from the lower Missouri Valley through
   Saskatchewan/Manitoba, while a significant short wave trough digs
   southeast of the lower Great Lakes/St. Lawrence Valley through the
   northern and middle Atlantic Coast region,

   In lower latitudes, Cristobal is forecast to slowly migrate
   northward within weak mid-level troughing, north of the Yucatan
   Peninsula through central Gulf of Mexico.  A mid-level low over the
   subtropical eastern Pacific is already accelerating northeastward
   toward southern California/northern Baja, in response to the digging
   mid-latitude trough, and models indicate that it will rapidly
   accelerate inland, north-northeastward across the Southwest through
   southern Saskatchewan and Manitoba Saturday through Saturday night.

   The subtropical perturbation appears likely to become increasingly
   sheared and absorbed within evolving larger-scale mid-level
   troughing, to the west of the mid-level ridge axis.  However, models
   indicate it will maintain considerable strength through this period,
   and contribute to significant surface cyclogenesis within lee
   surface troughing across eastern Montana into southern Saskatchewan
   by late Saturday night.

   This will, however, be preceded across much of the northern plains
   and Upper Midwest by an intrusion of relatively cool, dry low-level
   air, associated with the troughing digging into the Northeast. 
   While the front advances southward through much of the Northeast,
   Mid Atlantic and Ohio Valley, it may remain quasi-stationary across
   northeast Montana and the western Dakotas through much of the day,
   before retreating northeastward in response to the developing
   cyclone Saturday night.

   ...Northern portions of the plains...
   While cool/stable boundary-layer air holds firm across much of North
   Dakota and northern/eastern South Dakota through the day,  models do
   indicate moisture return within a relatively narrow warm sector of
   the developing surface low, east through north of the Black Hills
   vicinity by late Saturday afternoon.  Beneath relatively steep
   lower/mid tropospheric lapse rates, this may contribute to
   moderately large mixed-layer CAPE on the order of 2000 J/kg.

   In response to the impulse emerging from the Southwest, and perhaps
   a lower amplitude preceding perturbation or two, storms my initiate
   in the drier and more strongly heated/deeply mixed environment
   northwest through southwest of the Black Hills into the western
   Nebraska Panhandle Saturday evening.  Aided by strong deep-layer
   shear associated with a 50-70 kt southerly 500 mb speed maximum,
   this activity may organize and intensify while spreading
   northeastward/eastward through the northern high plains and toward
   the middle Missouri Valley.  This activity may be preceded by more
   discrete supercell development near the front, north and east of the
   Black Hills, before continuing to grow upscale and perhaps pose
   increasing potential for damaging winds, in addition to large hail. 
   Severe weather potential may continue into the middle Missouri
   Valley Saturday evening, before diminishing in more stable air
   across North Dakota and northeastern South Dakota.

   ...Northeast/Mid Atlantic vicinity...
   Considerable spread is evident within the various model output
   concerning convective potential associated with the digging upper
   trough and associated cold front.  However, it appears that
   destabilization and shear may become at least marginally conducive
   to organized strong to severe storm development in a couple areas
   Saturday, one near the lower/mid-level low center migrating across
   Maine, and one within pre-frontal surface troughing to the lee of
   the central Appalachians.

   ..Kerr.. 06/05/2020

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