Valid 061630Z – 071200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF THE NORTHERN PLAINS…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
THE LOWER OHIO VALLEY…
…SUMMARY…
Scattered severe thunderstorms are expected across the northern
Plains late this afternoon and evening, particularly across parts of
the central/eastern Dakotas and eastern Nebraska, where storms may
become capable of producing very large hail and damaging wind gusts.
Other storms with locally strong to severe wind gusts are expected
over a portion of the lower OH Valley region.
…Northern and central Plains region…
A corridor of richer low-level moisture with low 60s F dewpoints
will advect northward into the northern Plains ahead of a
southeast-advancing cold front and beneath a plume of steep
mid-level lapse rates. With strong diabatic heating, these processes
will result in moderate instability from southern ND through SD into
NE with up to 2000-2500 J/kg MLCAPE expected. Most CAM solutions are
similar with evolving scenario indicating storms will initiate over
southern ND where the cold front intercepts the corridor of richer
low-level moisture and where the cap should weaken sufficiently with
deep boundary layer mixing by late this afternoon. A belt of
stronger northwesterly mid-level winds will overspread this region
contributing to 40-50 kt effective bulk shear. Supercells with the
potential for very large hail will be the initial primary threat,
though a brief tornado or two cannot be ruled out. Storms will
eventually evolve into lines/clusters as they develop south, with
primary threat transitioning to damaging wind into the evening.
…Lower Ohio Valley region…
Strong diabatic heating of a moist boundary layer with low 70s F
dewpoints will result in moderate to strong instability 2000-2500
J/kg MLCAPE in this region this afternoon. WV imagery shows a
shortwave trough embedded within a northwesterly flow regime over IA
moving southeast. At least modest forcing for ascent attending this
feature and convergence along a front and pre-frontal trough should
be sufficient to initiate storms from southern IL, southwest IN into
western KY this afternoon. Northwesterly wind profiles with 30-35 kt
above 700 mb and steepening low-level lapse rates should be
sufficient for some storms to produce locally strong to damaging
wind gusts through early or mid evening.
..Dial/Bentley.. 08/06/2019
$$