LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1257 AM CDT Sat Sep 23 2023
Valid 231200Z - 241200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
MISSOURI VALLEY INTO NORTHEAST OKLAHOMA...
...SUMMARY...
Thunderstorms, associated with large to very large hail, wind
damage, and tornadoes, will be possible today across eastern parts
of the Great Plains, and Mississippi Valley. A couple of tornadoes
are also possible in parts of the Mid-Atlantic.
...Eastern Great Plains/Mississippi Valley...
Early-morning water-vapor imagery depicts a well-defined upper low
over northern WY, advancing east toward the Black Hills, in line
with latest model guidance. 60kt 500mb speed max is forecast to
translate across NE to near FSD by 18z, then into northern MN during
the overnight hours. This evolution will encourage a surface low to
lift into northeast NE by 18z, with some deepening expected during
the latter half of the period as the low occludes over southeastern
ND by 24/12z.
A north-south cluster of strong convection has evolved ahead of the
upper trough over the High Plains from western NE into southwestern
SD. This activity may continue through sunrise as it propagates
east, aided by large-scale ascent ahead of the trough. Additionally,
latest model guidance suggests LLJ will strengthen ahead of this
activity into western IA by mid day such that renewed development is
likely. NAM aggressively strengthens the LLJ in excess of 60kt over
south-central MN by late afternoon. Wind profiles and low-level
shear will strengthen ahead of the deepening surface low. This
supports the potential for supercells across the upper MS Valley,
especially near/south of the northward-advancing warm front.
Forecast soundings exhibit strong shear with substantial sfc-3km
SRH, though lapse rates will remain weak. Aside from the threat for
damaging winds with this pre-frontal activity, it appears
environmental conditions also support a tornado risk. In addition to
supercell threat, large-scale forcing may encourage some clustering
and potential line segments. Severe risk will spread into central MN
by late evening as the low occludes over the upper Red River (of the
North) Valley.
Farther south, high-level difluent flow will be noted across the
lower MO Valley into eastern OK. 500mb flow is expected to
strengthen south of I-70 to near the TX/OK Red River as weak height
falls will be noted at these lower latitudes. Surface front will
advance into eastern KS, arcing across central OK into northwest TX
by late afternoon. Strong boundary-layer heating will be noted ahead
of this wind shift, with surface temperatures forecast to rise into
the mid 90s to near 100F from portions of western OK into northwest
TX. As a result, convective temperatures will be breached as CINH is
reduced. Scattered thunderstorms should readily develop along the
wind shift, initially over eastern KS, then southwest along the
boundary at least into central OK. Forecast soundings exhibit
seasonally steep lapse rates with high PW values (approaching 2
inches). Wind profiles strongly favor organized convection and
initial activity should be supercellular in nature. With time, one
or more MCSs may ultimately evolve over the ENH Risk area, with
southward propagation expected across eastern OK/western AR late in
the period. Hail should be common with the initial activity, some of
it likely exceeding 2 inches in diameter. While a few tornadoes may
be noted with the supercells, storm mode may ultimately lead to a
complex that could produce damaging winds as convection spreads
southeast during the overnight hours.
...TS Ophelia...
Ophelia will soon move onshore along the NC Coast, then advance
inland before arcing northeast toward the Delmarva late in the
period. Strong low-level shear will develop across the southern
Middle Atlantic east of the low track. Convection that develops
across this region will be sufficiently sheared for supercells and
possibly a few tornadoes, in addition to gusty winds.
..Darrow/Moore.. 09/23/2023
Read more CHECK UPDATE ZOOM GRAPHIC
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