SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0245 PM CDT Thu Aug 10 2023
Valid 102000Z - 111200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID MISSOURI VALLEY AND VICINITY...
...SUMMARY...
Isolated severe thunderstorms remain possible over parts of the
eastern and central states this afternoon into tonight, including
eastern North Carolina/southeast Virginia and parts of the Upper
Midwest vicinity.
...Discussion...
The main outlook adjustment being implemented in this update, aside
from minor/local tweaks of the areal outlines, is an expansion of
MRGL risk across the Iowa vicinity. Expectations are that an at
least loosely organized MCS will move across the Iowa vicinity
overnight, and that local/low-end severe potential may accompany the
strongest cells.
Otherwise, no appreciable changes appear necessary at this time.
..Goss.. 08/10/2023
.PREV DISCUSSION... /ISSUED 1139 AM CDT Thu Aug 10 2023/
...Eastern Carolinas/southeast Virginia...
A convectively augmented shortwave trough over the southern/central
Appalachians will continue eastward today. A cluster of
thunderstorms, likely MCV aided, is ongoing across coastal areas of
the Carolinas at late morning. Although considerable cloud cover
immediately preceding the cluster may be a thermodynamic hindrance,
more appreciable destabilization is expected in more immediate
coastal areas. Where storms intensify, a seasonally
strong/cyclonically curved belt of westerlies (50+ kt at 500 mb)
would support organized storms including the possibility of a few
supercells and well-organized/moderately fast-moving clusters
capable of wind damage and some tornado risk.
Although uncertain, there is a scenario is which a secondary round
of regional convective development occurs late this afternoon near
the southeastward-moving weak front and/or preceding surface trough.
While deep-layer shear will tend to weaken late this afternoon/early
evening, wind profiles should conditionally remain supportive of
well-organized storms, potentially including a few supercells. This
could yield some storms capable of damaging winds, hail, and
possibly a tornado, prior to the risk abating/shifting offshore by
mid-evening.
...Dakotas/Upper Midwest and eastern Nebraska...
As a mid/upper ridge shifts east, a low-amplitude trough will
overspread the northern Great Plains. This will help induce a weak
surface cyclone over western North Dakota with a surface trough
arcing south into central Nebraska and a warm front extending
southeast through southern Minnesota. Relatively modest
boundary-layer moisture and deep-layer shear will be limiting
factors to a more prolific severe threat across the region. But
steeper mid-level lapse rates within an elevated mixed layer will
spread east across most of South Dakota and much of Nebraska by
early evening and support a confined corridor of moderate buoyancy
with MLCAPE of 1000-2000 J/kg. Effective bulk shear of 25-35 kts
should support a mixed mode of a few supercells and multicell
clusters.
The most likely zone for scattered thunderstorm development in the
late afternoon should be near the surface trough/warm front
intersection in the northeast South Dakota border area with ND/MN.
Increasingly isolated development should trail south along the
trough. A mix of large hail and severe wind gusts will be the main
threats, with some potential that an MCS evolves and continues
southeastward this evening.
...Mid-South/Tennessee Valley...
Modifying outflow from early day thunderstorms should serve as a
focus for redevelopment later this afternoon, along the remnant
front to the north. Additionally, another round of low-level warm
theta-e advection-driven storms should occur after sunset tonight. A
modest combination of mid-level lapse rates and vertical shear
should support a mainly isolated severe threat, with sporadic
instances of damaging gusts and marginal hail possible.
...Coastal Mid-Atlantic/southern New England...
Low-level warm theta-e advection will strengthen today and translate
northeast from the Mid-Atlantic across New England this afternoon
and evening. Low-topped convection (perhaps void of lighting flashes
in some cases) should develop amid meager surface-based instability
as thermodynamic profiles become saturated. Aside from localized
wind damage, the potential for a brief tornado also exists owing to
enlarged low-level hodograph curvature.
...Central High Plains...
Isolated high-based thunderstorms should develop off the higher
terrain of southeast Wyoming and far north-central Colorado near a
lee surface trough. A deep mixed boundary layer along the adjacent
High Plains could support a few severe wind gusts during the late
afternoon to early evening.
...West-central/northwest Texas...
Hot surface temperatures along the dryline may support isolated
thunderstorm development late this afternoon and early evening.
Should deep convection become sustained, the very deeply mixed
boundary layer could yield a few severe-caliber wind gusts.
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