SPC AC 081252

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0752 AM CDT Sat Jun 08 2019

   Valid 081300Z - 091200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN PORTIONS OF THE
   CENTRAL PLAINS...AS WELL AS THE EASTERN NORTH DAKOTA/NORTHWESTERN
   MINNESOTA AREA...

   ...SUMMARY...
   The greatest potential for severe storms will be over parts of the
   central Great Plains and Red River of the North area, with large
   hail and severe gusts expected.

   ...Synopsis...
   A split-flow pattern will persist in mid/upper levels, related to a
   large but weak cyclone now centered over middle TN.  This feature is
   expected to remain generally near its current location through the
   period, but with continued gradual filling, and perhaps transition
   to a broad open-wave trough overnight.  Associated mid/upper winds
   accordingly are forecast to weaken through the period, though
   several convectively induced/enhanced vorticity lobes will traverse
   the cyclonic flow over the Southeast States.

   Meanwhile, a synoptic-scale, northern-stream trough -- initially
   evident in moisture-channel imagery from the AB/SK line across
   northwestern MT, ID and northern NV -- will move eastward through
   the period.  By 12Z, this trough should reach the Dakotas, southern
   WY and northern UT.

   The 11Z surface analysis showed a low near the MB/ND/MN border
   junction, with cold front to southwestern SD and south-central WY.
   This front will move slowly eastward/southeastward through the day.
   By 00Z, the front should extend from northwestern MN across eastern
   SD and central NE, intersecting a dryline near the KS/CO border, to
   a surface low over southeastern CO.  The dryline will extend
   southward through the TX/OK Panhandles to the lower Pecos Valley and
   Big Bend regions.

   ...Northern/central Plains to southern High Plains...
   Scattered thunderstorms are forecast to form near the cold front
   from the eastern Dakotas to near the KS/CO border, offering severe
   hail and gusts early in the convective cycle when cells are
   relatively separated.  As convection aggregates near the front, wind
   will become the more predominant concern.  Large hail, some
   potentially above 2 inches in diameter, appears most probable where
   supercell mode can be sustained the longest, which currently appears
   to be in the area east and southeast of the front/dryline
   intersection.

   The most concentrated overall potential still appears to be over the
   central High Plains, where lapse rates and buoyancy will be
   greatest, and near the Red River of the North, in the zone of
   greatest deep-layer forcing.  Additional, isolated to widely
   scattered convection -- potentially including a few supercells --
   should form in the post-frontal/upslope flow regime of northeastern
   CO where low-level shear is maximized (but CAPE is weaker than areas
   along/ahead of the front), and near and south of the front/dryline
   intersection into western KS.

   Favorable diurnal heating and a corridor of 50s to low 60s F
   prefrontal surface dew points will support weakening MLCINH and the
   development of around 1500-2000 J/kg MLCAPE in the northern Plains,
   and 2000-2500 J/kg across portions of KS/NE east of the front and
   dryline.  Forecast soundings suggest 40-45-kt effective-shear
   magnitudes will exist near the front and the KS/CO portion of the
   dryline, with vectors more orthogonal to the forcing boundaries
   (favoring longer discrete character) over the central High Plains.

   ...Southern High Plains...
   A conditional and very isolated severe hail/wind threat is evident
   farther south across the TX/OK Panhandles to the Permian Basin and
   lower Pecos Valley region, ahead of the dryline.  Forcing for ascent
   in this corridor will be very localized, related to strong surface
   heating and the intensity of the vertical circulations in the
   moisture gradient.  Any mature storm(s) that develop will move atop
   a well-mixed subcloud layer amidst steep midlevel lapse rates, and
   MLCAPE in the 1000-2000 J/kg range.  Uncertainties regarding
   coverage/duration of convection preclude more than a marginal
   unconditional risk at this time, though significant wind or hail
   cannot be ruled out under any sustained cell that develops.

   ...Southeastern CONUS...
   Widely scattered to scattered thunderstorms should develop from
   midday through this evening across this region, preferentially
   favoring outflow, differential-heating and sea-breeze boundaries. 
   The preconvective air mass again will be characterized by strong
   heating in relatively cloud-free preconvective areas, rich low-level
   moisture, with PW 1.75-2.25 inches, mean mixing ratios 16-18 g/kg,
   and surface dew points commonly in the 70s F.  Though a rogue
   damaging or severe gust cannot be ruled out in the water-loaded core
   of virtually any surface-based cell in the region, the most favored
   area for marginally severe gusts should be southeast of the
   mid/upper low, in and near the "marginal" outlook area, beneath a
   belt of 25-35 flow atop the boundary layer that will enhance
   low-level shear and storm-relative flow somewhat, in favor of
   organized multicells or brief supercell characteristics.

   ..Edwards/Goss.. 06/08/2019

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