LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Sun Aug 06 2023
Valid 061300Z - 071200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MID-MS AND LOWER
OH VALLEYS TO THE MID-SOUTH AND SOUTHEAST...
...SUMMARY...
A few tornadoes along with scattered damaging winds and large hail
will be possible from late afternoon into tonight from the
Mid-Mississippi to Lower Ohio Valleys. Scattered damaging winds will
also be possible, mainly from midday into early evening across parts
of the Mid-South and Southeast.
...Mid-MS to Lower OH Valleys...
In the wake of decaying convection over northeast MO and AR/OK, a
plume of at least moderate buoyancy should develop towards peak
heating across the Mid-MS Valley. Guidance is fairly consistent that
an arc of thunderstorms will develop during the mid to late
afternoon across southeast IA into northeast MO downstream of the
eastward-drifting shortwave trough and attendant surface cyclone
over the Mid-MO Valley. The impinging of a 700-mb speed max across
MO into IL will enhance 0-3 km SRH and foster supercell development
despite predominantly west-southwesterly low-level flow. Modest
mid-level lapse rates (especially with eastern extent) may curtail
greater updraft intensity. But with at least a few supercells
expected, there will be potential for large hail up to around 2
inches and a couple tornadoes. Towards late evening, upscale growth
into one or two organized clusters seems plausible, with potential
for an MCS to evolve along the northern extent of the surface-based
instability plume. An elongated swath or two of damaging winds with
embedded severe gusts, along with a couple brief tornadoes may be
sustained into the early overnight into the Lower OH Valley.
...Mid-South to the Southeast...
There is uncertainty whether a decaying MCS near the AR/OK border
will completely subside by late morning owing to nearly cloud free
insolation underway downstream of its remnant outflow. This boundary
will likely serve as a focus for renewed thunderstorm development
from midday through the afternoon as it spreads east of the Lower MS
Valley into the Southeast. While the leading outflow will outpace
stronger mid-level flow attendant to the slow-moving trough over the
Mid-MO Valley, impinging of 25-35 kt 700-mb westerlies from the TN
Valley northward should be adequate to support semi-organized
multicell clusters amid an extensive plume of large buoyancy across
the Deep South. Scattered damaging wind swaths from water-loaded
downbursts will be possible through early evening. Have expanded
both the cat 1 and 2 risks southward to account for a more southern
evolution of clusters.
During the evening, low-level warm theta-e advection should
strengthen along the trailing outflow/effective baroclinic zone over
the Mid-South. This activity should pose an isolated threat for
severe hail initially before likely clustering into a localized
damaging wind threat overnight.
...Central/southern Rockies...
The presence of 50s surface dew points will support potential for
isolated but regenerative thunderstorms to develop along the Front
Range during the late afternoon and evening. While the NAM appears
much too cool across the adjacent plains, MLCIN should steadily
increase with eastern extent. This should yield a rather confined
corridor for weak buoyancy with MLCAPE of only 500-1000 J/kg.
Nevertheless, deep-layer wind profiles will be quite favorable for
supercells and large hail potential given near-perfectly
straight-line hodographs. After collaboration with WFOs PUB/BOU have
held at upgrading to a cat 1-MRGL risk for now, but a meso-beta
scale corridor of cat 2-SLGT risk for hail may be warranted in later
outlooks.
Downstream of a minor shortwave trough over the interior Northwest,
isolated to scattered afternoon thunderstorms are anticipated around
the UT/WY/CO border area within a weak buoyancy plume. Adequate
deep-layer shear will exist for a threat of marginally severe hail
and wind centered on the late afternoon.
...Central/southern Appalachians to Lake Erie...
A trio of MCVs, one over northern IN and the others over eastern
KY/TN, will aid in scattered thunderstorm development downstream of
these features from midday through the afternoon. Instability will
be substantially weaker relative to the TN Valley region, owing to
both weaker mid-level lapse rates and buoyancy. Pockets of stronger
low to mid-level flow attendant to these MCVs may support sporadic
localized damaging winds.
..Grams/Broyles.. 08/06/2023
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