SPC AC 271300

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0800 AM CDT Sat Mar 27 2021

   Valid 271300Z - 281200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
   MID-SOUTH AND TENNESSEE VALLEY...

   ...SUMMARY...
   Severe storms are likely across the lower Mississippi through
   Tennessee Valley regions today into tonight. All hazards are
   possible including large hail, damaging wind, and tornadoes,
   potentially including a strong tornado risk from southern/eastern
   Arkansas into northern Mississippi and western Tennessee. Other
   severe storms are possible across the Midwest, with isolated
   damaging wind and severe hail being the main threats.

   ...ArkLaTex/Mid-South and Tennessee Valley...
   Supported by elevated moisture transport near/north of a warm front,
   scattered strong to locally severe thunderstorms are ongoing in the
   predawn hours across far northern Mississippi/southwest Tennessee
   into Middle/eastern Tennessee. Isolated severe hail will be possible
   early today, although continued storm mergers/further upscale growth
   should curb hail magnitudes while otherwise potentially yielding a
   few damaging wind gusts, especially with the storms in closer
   proximity to the warm front. For additional short-term details, see
   Mesoscale Discussion 276. That said, a more consequential severe
   risk is anticipated across the region later this afternoon and
   tonight.

   An upstream positively tilted shortwave trough over southern
   portions of Arizona/New Mexico early today, as well as a more
   substantial upper trough crossing the Dakotas/Upper Midwest, will
   influence height falls/cyclogenesis over the region but not until
   later tonight. Regardless, a semi-persistent warm/moist conveyor may
   continue to yield showers/thunderstorms in vicinity of the warm
   front, with this rain-cooled air/outflow likely being a significant
   factor (and point of uncertainty) across east/northeast Arkansas and
   western/Middle Tennessee (and areas to the north) regarding the
   northern extent of the later-day peak severe risk.

   To the south/southwest of these early day storms, in conjunction
   with middle/upper 60s F surface dewpoints, the strongest low-level
   heating/destabilization is expected across northeast Texas/ArkLaTex
   and southern/eastern Arkansas into northern Mississippi and
   southwest Tennessee, where MLCAPE should reach 2000-2500 J/kg.
   Initial development/maturation of surface-based storms should occur
   by around 3-6 pm CDT within this corridor. 

   Forecast wind profiles favor supercells and lapse rates should be
   sufficiently steep for isolated very large hail with these storms.
   As low-level shear/SRH considerably strengthens, a couple of strong
   tornadoes (EF2+) will be possible, particularly late this afternoon
   into evening, across southern/eastern Arkansas into northern
   Mississippi and western Tennessee. However, the anticipated
   evolution of a somewhat mixed convective mode, coincident with the
   timing of enlarging low-level hodographs toward/after sunset, leads
   to some uncertainties regarding higher-end tornado potential.

   An upscale-growing quasi-linear convective system will likely
   organize and accelerate eastward this evening into the overnight,
   with damaging winds becoming an increasing concern aside from a
   QLCS-related tornado risk as storms spread across southeast
   Arkansas, northern portions of Mississippi/Alabama, and much of
   Tennessee. 

   ...Midwest...
   Strong mid-level height falls will overspread the Upper Midwest
   region in advance of a northern branch shortwave trough. It is still
   not entirely clear how much moisture/instability will be drawn north
   ahead of the surface low into eastern Missouri/Illinois prior to
   convective initiation. Regardless, at least an isolated severe
   hail/wind risk is expected late this afternoon into evening across
   Illinois/eastern Missouri and eventually into Indiana near the
   eastward-advancing cold front.

   ..Guyer/Kerr.. 03/27/2021

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