SPC AC 291713

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1213 PM CDT Sun Aug 29 2021

   Valid 301200Z - 311200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
   GULF COAST...AND ACROSS PARTS OF SOUTH DAKOTA AND NEBRASKA...

   ...SUMMARY...
   Tornadoes are possible within the right-front quadrant of tropical
   cyclone Ida across portions of the Lower Mississippi Valley and
   Southeast on Monday. Severe storms are also possible across parts of
   South Dakota and Nebraska.

   ...Lower MS Valley/Southeast - Hurricane Ida...

   Tropical cyclone Ida is forecast to track north/northeast across the
   lower MS Valley on Monday, with a position near the MS/AL/TN
   tri-state area by Tuesday morning. Strong low level wind fields will
   maintain strong vertical shear near the storm center and within the
   eastern semi-circle. Surface dewpoints are generally expected to be
   in the 73-76 F range, with some pockets of stronger heating possible
   across parts of southern MS/AL. Low level instability and more
   favorable conditions supporting tornadogenesis will reside where
   surface dewpoints in the mid-70s F are present amid stronger
   heating, and currently expected to be centered over southeast
   MS/southwest AL. However, the broader tropical airmass and strong
   low level shear will maintain a tornado threat across much of
   southeast LA, MS/AL and portions of TN/GA and the FL Panhandle as
   Ida lifts north/northeast through the forecast period. 

   ...Northern/Central Plains...

   Uncertainty remains regarding severe potential across parts of the
   northern/central Plains on Monday. The bulk of forecast guidance
   indicates some ongoing convection within a band of warm advection
   across parts of south-central SD into eastern NE Monday morning.
   This activity is likely to be elevated, but given favorable
   effective shear magnitudes and steep midlevel lapse rates, some
   threat for hail could accompany this activity. How widespread early
   convection is, and how long it persists will have implications for
   afternoon thunderstorm development and evolution of severe potential
   into Monday evening. 

   At least a narrow corridor of moderate to strong instability with
   minimal capping is expected from near the Black Hills into central
   NE. Large-scale forcing is expected to remain weak, though forecast
   guidance indicates subtle shortwave impulses migrating through
   west/northwesterly flow during the afternoon/evening. Convection
   could redevelop along outflow from morning storms across NE, but
   also in upslope flow/low level convergence near the higher terrain
   of the Black Hills. Initial activity may remain discrete long enough
   to produce very large hail and strong gusts. As a low level jet
   increases during the evening, upward development into a linear
   convective system is possible, shifting east/southeast across parts
   of southern SD and central/eastern NE. Low level shear will be weak,
   but small, favorably curved hodographs and mid-60s surface dewpoints
   could support a tornado or two as well. 

   More isolated storms capable of hail and gusty winds are possible in
   moist, upslope flow over southwest ND during the late
   afternoon/evening. 

   ...Northeast...

   A seasonally warm/moist airmass will exist across New England ahead
   of an eastward-advancing cold front. Stronger heating is expected
   near the coast and into southern New England, resulting in MLCAPE
   around 750-1000 J/kg. Vertical shear is expect to remain modest
   (around 25-30 kt) and lapse rates will be poor, limiting
   stronger/more organized convection. However, a few strong storms
   could produce locally strong gusts through the afternoon.

   ..Leitman.. 08/29/2021

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