SPC AC 151948

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0248 PM CDT Sun Sep 15 2024

   Valid 152000Z - 161200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTHERN/CENTRAL PLAINS...

   ...SUMMARY...
   Thunderstorms capable of producing isolated severe gusts and hail
   may occur today and tonight across parts of the northern/central
   Plains.

   ...20z Update...
   Only minor adjustments were made to the D1 Convective Outlook to
   account for latest observational trends. See previous discussion
   below for more information.

   ..Thornton/Gleason.. 09/15/2024

   .PREV DISCUSSION... /ISSUED 1128 AM CDT Sun Sep 15 2024/

   ...Northern/Central Plains...
   An amplified upper trough along/near the West Coast this morning
   will further evolve into a closed upper low over northern CA and
   vicinity by late tonight. Ahead of this feature, modestly enhanced
   south-southwesterly mid-level flow will be in place over much of the
   western states and Rockies through the period. Although low-level
   moisture is expected to remain limited over much of this region,
   isolated strong to severe gusts may occur with any thunderstorms
   that can develop in a deeply mixed boundary layer favorable for
   gusty downdraft winds. 

   Latest guidance continues to suggest that a relatively greater
   concentration of severe potential will be focused across parts of
   the northern/central Plains late this afternoon through tonight.
   Across this area, a weak surface lee trough and greater low-level
   moisture to its east should support weak to moderate instability
   with daytime heating. Steep mid-level lapse rates should also aid
   updraft accelerations/intensities, with around 20-30 kt of
   deep-layer shear supporting modest thunderstorm organization.
   Isolated severe hail may occur with initially more discrete
   convection, but a tendency for clustering should lead to a
   relatively greater wind threat with time as convection spreads
   generally east-northeastward through the evening. Regardless, the
   overall severe threat from northeast CO into western NE/SD and
   vicinity should remain fairly isolated/marginal given the modest
   deep-layer shear.

   Low-level warm advection is forecast to increase across much of the
   northern/central Plains tonight as a southerly low-level jet
   strengthens. A surface warm front is also expected to lift northward
   over ND late tonight into early Monday morning. With steepening
   mid-level lapse rates overspreading the northern Plains in tandem
   with increasing low-level moisture, ample MUCAPE should be
   available. Most guidance shows at least isolated convection
   developing across parts of ND tonight in this favorable
   thermodynamic environment. Although deep-layer shear may remain
   fairly modest, it may still be sufficient for updraft organization
   and an isolated threat for severe hail with any elevated convection
   that can form. Have therefore expanded the Marginal Risk northward
   to account for this potential.

   ...Coastal Carolinas...
   Latest NHC forecast continues to indicate some potential for
   sub-tropical or tropical development of a surface low currently off
   the SC Coast. Regardless of development, it still appears that the
   more moist/tropical low-level airmass over the Gulf Stream will
   struggle to advance inland over coastal portions of NC/SC through
   the end of the Day 1 forecast period early Monday morning (16/12Z).
   Accordingly, tornado potential with any low-topped supercells on the
   north to northeast periphery of the surface low should tend to
   remain offshore until Day 2/Monday (after 16/12Z).

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z