SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0249 PM CDT Sat Sep 23 2023
Valid 232000Z - 241200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF EASTERN KANSAS...NORTHEASTERN OKLAHOMA...WESTERN
MISSOURI...EXTREME NORTHWESTERN ARKANSAS...
...SUMMARY...
Large to very large hail, wind damage and a few tornadoes remain
possible today across parts of the Upper Midwest, Lower Missouri
Valley to the southern Plains. A tornado or two may also occur in
parts of the coastal Mid-Atlantic.
...20Z Update...
The main change made to this outlook was to trim southern portions
of severe probabilities across the Mid Atlantic in tandem with the
passage of Ophelia. Some uncertainty remains pertaining to the
details of convective evolution across portions of the Upper
Midwest, hence no changes have been made to the outlook. Though
storms have reduced instability some across the MS Valley, enough
heating is underway which could modify the airmass enough to support
a few additional strong to severe storms.
Otherwise, the rest of the forecast remains on track, with
additional supercells likely to develop across southeastern KS into
eastern OK and western MO with a threat for severe gusts and very
large hail. A few tornadoes also remain possible, especially over
far eastern SD into southern MN, where backed low-level flow
supports enlarged hodographs.
..Squitieri.. 09/23/2023
.PREV DISCUSSION... /ISSUED 1139 AM CDT Sat Sep 23 2023/
...Upper Midwest/Lower Missouri Valley/Southern Plains...
A cluster of storms with history of periodic large
hail/severe-caliber wind gusts this morning across eastern Nebraska
persists into western Iowa at midday, while generally trending
downscale and a bit weaker. These storms seem likely to outpace the
primary reservoir of buoyancy with greater early-day inhibition with
eastward extent, but some short-term severe risk may nonetheless
continue.
This convection casts some uncertainty regarding the northward
extent of more appreciable surface-based destabilization later
today, but strong/potentially severe thunderstorm redevelopment is
still expected later this afternoon near the surface wind
shift/occluded front. This would primarily be the case beginning
around mid/late afternoon, coincident with the approach of the upper
vort/speed max over South Dakota/northern Nebraska/northwest Iowa
vicinity. At least a modest corridor of severe-conducive instability
may materialize especially across northwest Missouri/west-central
Iowa and southwest/south-central Minnesota. Supercell-favorable
hodographs will reside across much of the region, with the potential
for large hail, damaging winds, and possibly tornadoes, particularly
if more cloud breaks/destabilization occurs in proximity to the
surface low/triple point.
Farther south, another corridor of persistent convection since
mid-morning has been across far eastern Kansas into
northwest/western Missouri. These storms have occasionally produced
severe hail, and this may continue for a time this afternoon even as
warm advection/850 mb convergence weakens.
The primary scenario is otherwise expected to near-frontal deep
convective development late this afternoon into evening, with a
moderate to strongly unstable environment, particularly to the
southwest of the eastern Kansas/northwest Missouri early day storms.
Steep lapse rates/ample buoyancy and enlarged hodographs will
support initial supercell potential, capable of very large/damaging
hail, severe wind gusts and possibly some tornado risk, with storms
tending to grow upscale during the evening.
CAPE will lessen somewhat with southwestward extent into
north-central/northwest Texas where greater boundary-layer mixing
and lesser dewpoints will be found, but with greater DCAPE and
downdraft-acceleration potential in support of local wind threat.
...Mid-Atlantic States/Tidewater...
Currently centered over northeast North Carolina, Tropical Storm
Ophelia is expected to continue to weaken as it generally moves
north-northeastward through tonight. Reference the National
Hurricane Center for latest details. Even while the system will
gradually weaken, some tornado risk will focus along coastal areas
of southeast Virginia toward the Delmarva today, and possibly
eventually as far north as New Jersey. Any such potential is
expected to generally relate to convection that can deepen/sustain
and pivot toward the coast, especially if it interacts with the warm
front where low-level/deep-layer shear will be maximized with
surface-rooted buoyancy.
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