SPC AC 021251

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0751 AM CDT Tue Jul 02 2024

   Valid 021300Z - 031200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   SOUTHERN IOWA...NORTHERN MISSOURI...NORTHEASTERN KANSAS...AND
   EXTREME SOUTHEASTERN NEBRASKA...

   ...SUMMARY...
   Damaging thunderstorm winds, a few tornadoes, and large hail are
   most likely this afternoon and early evening over southern Iowa,
   northern Missouri, and northeastern Kansas.

   ...Synopsis...
   Broadly cyclonic flow in mid/upper levels will persist from the
   Pacific Northwest across the central/northern Rockies to the Upper
   Great Lakes.  Within that, a series of shortwave troughs were
   apparent, the most prominent over the CONUS being located initially
   across WY and northeastern UT.  This perturbation should move
   eastward to eastern SD and central NE by 00Z, cross the upper
   Mississippi Valley overnight, and reach parts of WI and the Upper
   Peninsula of MI by the end of the period.  As that occurs, a
   persistent subtropical high over the Arklatex region will shift
   eastward over the Delta region, but with attached ridging expanding
   back across central and west TX to near ELP.  Another attached ridge
   will shift eastward across the Ohio Valley and Lower Great Lakes.

   At the surface, 11Z analysis showed a surface low near HLC, with
   cold front southwestward across extreme southeastern CO and
   northeastern/north-central NM.  A warm front arched from the low
   across southeastern NE, then southward near the KS/MO and AR/OK
   borders.  The warm front should move northeastward to the mid
   Mississippi Valley today while the low moves northeastward and
   weakens.  Meanwhile, by 00Z, the cold front should reach western IA,
   northeastern through south-central KS, and the northern TX
   Panhandle. becoming a warm front into a deepening low over
   southeastern CO.  By 12Z, the cold front should reach northern IL,
   central/southwestern MO, north-central OK, then into the low, which
   will have sagged into the northern TX Panhandle.

   ...IA/MO/northeastern KS and vicinity...
   A swath of decaying convection and associated cloud shield are
   ongoing from Lower MI to IA and parts of southeastern NE and
   northwestern MO.  This plume of clouds/precip should continue to
   shift east-northeastward and erode through the day, but leave behind
   an outflow/differential-heating boundary that, southwest of the
   synoptic warm front, should act as the primary convective influence
   ahead of the cold front.  Convergence near these boundaries, and
   strong heating in the richly moist warm sector between, will support
   scattered afternoon thunderstorms.  This will include the potential
   for a few supercells with tornado and large-hail threats, whether
   relatively discrete early in the convective cycle, or embedded in
   subsequent quasi-linear evolution.  That upscale convective
   organization also will maximize severe-wind potential from late
   afternoon into early evening, before activity encounters a
   more-stable, nocturnally cooling airmass farther east near the
   warm-frontal thermal gradient.

   In the preconvective warm sector, 70s F surface dewpoints should be
   common, as a Gulf-origin airmass blends with areas of
   evapotranspirative moisture contribution.  Though mid/upper-level
   lapse rates will be modest, strong low-level destabilization will
   combine with a deep troposphere to contribute to MLCAPE in the
   2000-3000 J/kg range.  Effective-shear magnitudes will have a large
   range -- roughly 35-55 kt based strongly on boundary effects upon
   near-surface winds.  Boundary-layer shear/hodographs will be
   greatest near the warm front and along any mesoscale boundaries
   between the fronts, locally maximizing supercell organization in low
   levels.

   ...Central/southern High Plains...
   Widely scattered to scattered thunderstorms are forecast to develop
   this afternoon over western portions of this area -- initially over
   relatively high elevations of southeast WY, east-central/
   southeastern CO and northeastern NM, where diurnal heating will
   preferentially erode MLCINH.  This activity should move generally
   eastward onto the adjoining High Plains, offering sporadic severe
   gusts and hail.  The greatest concentration of convection (and
   associated severe potential) still appears most probable over
   southeastern CO, growing upscale as a complex and moving into parts
   of southwestern KS this evening.

   Vertical shear will be most favorable for supercells north of the
   front, where a substantial easterly component of boundary-layer flow
   will contribute to enhanced low-level shear, greater storm-relative
   low-level winds, upslope lift, and moist advection (to offset
   mixing-related moisture loss somewhat).  The northern lobe of the
   (marginal) outlook area will be under the greatest mid/upper-level
   flow and strongest deep shear, but also will have weaker low-level
   moisture/theta-e and less buoyancy than farther south, with similar
   mid/upper-level lapse rates under a monsoonal plume as closer to the
   subtropical ridge.  In the Arkansas River Valley region, activity
   moving into 50s to low 60s F surface dewpoints, with a strongly
   heated boundary layer, will encounter peak diurnal MLCAPE of
   500-1500 J/kg across southeastern CO, and 1000-2000 J/kg into
   southwestern KS, amidst 45-55 kt effective-shear magnitudes, and
   long/nearly straight low-level hodographs favoring large hail with
   any discrete supercells.  However, a well-mixed subcloud layer
   should support severe outflow and aggregation of outflows, leading
   to upscale clustering for a few hours before activity encounters too
   much CINH to remain severe over southern/central KS.  Farther south,
   along and south of the front, deep-layer flow and shear will be
   weaker, as will buoyancy (due to drier, deeper mixed layers), but
   convection still may pose a threat for isolated severe downbursts.

   ..Edwards/Kerr.. 07/02/2024

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