ACUS01 KWNS 180552
SWODY1
SPC AC 180551

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1251 AM CDT Thu Jul 18 2024

Valid 181200Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS EASTERN NORTH
CAROLINA INTO FAR SOUTHEAST VIRGINIA...

...SUMMARY...
Isolated strong to severe thunderstorms are possible Thursday
afternoon across parts of north-central Montana and the central and
southern High Plains. Isolated to scattered severe thunderstorms are
also expected from the southern Appalachians into eastern North
Carolina.

...Synopsis...
Early-morning surface observations show a diffuse cold front draped
from the Mid-Atlantic region into the southern Plains. This feature
is expected to slowly push south over the next 24 hours, as surface
high pressure builds over the Plains/Midwest in the wake of an
eastward-tracking upper wave. A reservoir of upper 60s to low 70s
dewpoints lies to the south of the cold front, and while mid-level
lapse rates are fairly modest (based on 00 UTC soundings), diurnal
heating into the mid 80s should be sufficient to promote
thunderstorm development along the front by early afternoon.
Thunderstorm coverage is expected to be somewhat more focused across
the southern Appalachians into the Carolinas, as ascent associated
with a weak mid-level perturbation (currently over the mid-MS
Valley) overspreads the region at peak heating. To the west,
isolated to scattered thunderstorms appear likely within an upslope
flow regime along the central Rockies and ahead of a shortwave
trough over northern Montana.

...Carolinas...
The synoptic cold front is currently forecast to be along the VA/NC
border by around mid-day. Thunderstorm development along the front
appears probable by around 18 UTC, as temperatures warm into the low
80s and ascent from a subtle mid-level impulse overspreads the
region. Large hail may be an initial concern depending on storm
coverage along the front, but storm motion and deep-layer shear
vectors along and/or towards the cool side of the boundary will
likely promote upscale growth by mid/late afternoon. As this occurs,
the potential for strong to severe winds will increase downstream
across eastern NC and far southeast VA. Latest CAM guidance shows
reasonably good agreement in the development of a squall line, and
while deep-layer shear will not be overly strong (around 25 knots),
heating ahead of the line should yield moderate buoyancy with MLCAPE
reaching up to 2500 J/kg that will promote robust convection capable
of damaging gusts. The coverage of this threat appears sufficient to
warrant higher (15%) wind risk probabilities.

...Central to southern High Plains...
Another day of easterly upslope winds along the southern to central
Rockies is anticipated as a surface high to the east builds. Latest
upper-air analyses show the east slopes of the Rockies lie on the
periphery of a plume of relatively steep (7+ C/km) lapse rates. This
should support isolated to scattered thunderstorm development by mid
to late afternoon. Adequate deep-layer shear will be in place to
promote storm organization, including the potential for a supercell
or two if more discrete storm modes can be realized. However, weak
low-level storm-relative winds and steep low-level lapse rates will
likely favor cold-pool driven storm propagation and the development
of multiple convective clusters with an attendant severe-wind risk.

...Montana...
A shortwave impulse is evident in early-morning water-vapor imagery
across the Pacific Northwest. This feature is expected to crest the
apex of a stout upper ridge over the next 24 hours. Advected
precipitable water imagery shows a diluted plume of monsoonal
moisture ahead of this wave, which should provide adequate mid-level
moisture for thunderstorm development by late afternoon. While
buoyancy will be very modest (around 500 J/kg SBCAPE), 30 knot
mid-level flow atop easterly low-level winds should provide adequate
deep-layer wind shear for some storm organization, most likely into
somewhat cohesive clusters given deep-boundary layer mixing that
will favor strong cold pool production. Such clusters may be capable
of strong to severe winds as they push east across north-central MT.

..Moore.. 07/18/2024

$$
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