Severe weather thread

...SUMMARY...

Scattered severe thunderstorms capable of producing large hail,

damaging winds, and a few tornadoes may occur across parts of the

Lower Great Lakes, Midwest, and Ohio Valley regions on Sunday.



...Synopsis...

A split mid/upper-level jet structure will likely be present over

much of the western/central CONUS on Sunday, with modest 500 mb

height falls forecast to spread across the mid/upper MS Valley and

Great Lakes region through Sunday evening. Large-scale lift

associated with the strong southern branch of the mid/upper-level

jet (100+ kt at 250 mb and 60-70+ kt at 500 mb) should promote

convective development across parts of the lower Great Lakes,

Midwest, and OH Valley by Sunday afternoon. An elevated mixed layer

with steep mid-level lapse rates (generally 7-8 C/km in the

700-500-mb layer) emanating from the central/southern Plains is

expected to overspread these regions through the period.



At the surface, a broad moist warm sector will be in place across TX

and the lower MS Valley into parts of the Southeast, TN/OH Valleys,

Midwest, and lower Great Lakes. Surface dewpoints reaching into at

least the low to mid 60s should be common across the warm sector

Sunday afternoon. A weak surface low should develop northeastward

along a warm/cold front triple point from the vicinity of eastern

KS/western MO to the lower Great Lakes by Sunday evening. A trailing

cold front should progress slowly southeastward across the mid MS

Valley and parts of the Midwest/OH Valley through early Monday

morning.

...Arklatex to the Ohio Valley...

As the aforementioned shortwave trough continues northeast towards
the upper Midwest, a strong low-level jet is forecast to organize
across the Arklatex through the mid-day hours, before strengthening
and translating northeast towards the Ohio Valley through the
overnight hours. In conjunction with this evolution, the surface
warm sector (characterized by dew points in the lower/mid 60s along
its northern fringes) will stream northward, reaching areas from
southeastern Missouri to southern Indiana through the period. South
of the warm front, despite little/modest low-level heating and
related buoyancy, favorably moist low levels should support upwards
of 1000 J/kg of MLCAPE across parts of the Mid-South by afternoon,
with values decreasing to 200-400 J/kg across the Ohio Valley.


Countering these lower values of buoyancy, a strong kinematic
profile will evolve across much of the region, especially from
northern Arkansas to the lower Ohio Valley. Within this region,
925-850mb flow around 60-70 kt will contribute to sizable values of
storm-relative helicity through the evening hours. In turn, as a
narrow band of convection organizes from the Arklatex to the Ozarks
through the day, shear profiles should encourage several bowing/LEWP
structures, with embedded supercells possible. Furthermore, forecast
soundings and high-res guidance depict a considerable component of
low-level shear perpendicular to several bowing segments, enhancing
the potential for tornadoes -- a few of which could be strong --
during the afternoon and evening hours. These cells will then race
towards the Ohio and Tennessee Valleys during the evening and
overnight. Moist adiabatic low-level profiles, while not conducive
for high values of buoyancy, may still prove favorable for a few
swaths of damaging winds (with an attendant line-embedded tornado
threat), as any low-level rotating elements will enhance upward
vertical motion and convective intensity.


Outside of the main band of convection, although forcing for ascent
will not be particularly strong earlier in the day, an isolated
discrete supercell or two may form across the Mid-South within
warm/moist low-level confluence Saturday afternoon. Favorable
storm-relative helicity and effective shear would support a
conditional damaging wind and tornado threat during this time frame
as well.