176
ACUS01 KWNS 151629
SWODY1
SPC AC 151628

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1128 AM CDT Sun Sep 15 2024

Valid 151630Z - 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.

...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).

..Gleason/Moore.. 09/15/2024

$$