SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 PM CDT Thu Jul 06 2023
Valid 071200Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
CENTRAL AND SOUTHERN HIGH PLAINS INTO THE SOUTHERN PLAINS...
...SUMMARY...
Severe wind and hail producing storms are expected across the
central and southern High Plains into the southern Plains
tomorrow/Friday. A couple of damaging gusts are also possible across
the Upper Hudson Valley.
...Synopsis...
A pronounced mid-level trough will traverse the central CONUS while
a secondary mid-level perturbation crosses the southern Rockies and
ejects into the southern Plains tomorrow/Friday. Meanwhile, the
approach of the mid-level trough over the Midwest will also support
weak surface troughing along and to the lee of the central and
northern Appalachians during the afternoon hours. Multiple rounds of
organized strong to severe storm potential should occur across the
central U.S., including at the start of the period. The most robust
severe storm development should occur across the southern Plains
with the ejection of the mid-level perturbation, with all severe
hazards possible. Scattered strong thunderstorm development may also
occur across the northeast in tandem with the weak surface lee
trough.
...Southern High Plains into the southern Plains...
One or more loosely organized MCSs will likely be in progress over
portions of the southern Plains at the start of the period (12Z
Friday morning), perhaps accompanied by a marginal severe wind
threat. With time, as the low-level jet weakens, the MCSs should
dissipate through the late morning/early afternoon hours. Similar to
Day 1, residual showers and cloud cover will gradually clear,
allowing for surface temperatures to rise over 90 F in the TX
Panhandle, to over 80F points north. These temperatures, along with
surface dewpoints into the low to mid 60s F, overspread by 8.5+ C/km
mid-level lapse rates, will support strong buoyancy (i.e. 3000+ J/kg
SBCAPE), especially in the northern TX Panhandle. By late afternoon
into early evening, a 20-30 kt southwesterly low-level jet,
overspread by 40-50 kts of 500 mb westerly flow, will support 40-50
kts of effective bulk shear, characterized by hodographs with some
low-level curvature and mid-level elongation. Questions remain
regarding initial storm coverage (especially north of the TX
Panhandle) due to capping. However, at least isolated supercells
should initiate by late afternoon with a large hail threat. A few 2+
inch stones and a couple of tornadoes cannot be ruled out. Later in
the evening, upscale growth into a severe-wind producing MCS is
possible. The overall coverage and severity of this MCS is
predicated on the number and intensity of initial merging
supercells. The isolated nature of the initial supercells and lack
of higher confidence in robust MCS development precludes greater
severe wind/hail coverage probabilities this outlook.
...Northern Plains...
Behind the progressing mid-level trough, a weak cold front will sag
southward across the northern Plains during the day. Insolation and
boundary-layer mixing, overspread by 7 C/km mid-level lapse rates,
will foster 1000-2000 J/kg SBCAPE by afternoon peak heating.
Deep-layer shear will not be overly strong (i.e. generally under 30
kts of effective bulk shear). Nonetheless, enough hodograph
curvature/elongation may exist to support stronger pulse-cellular
storms or loosely organized multicell clusters with an isolated
severe gust threat along with some small hail.
...Midwest...
Thunderstorm clusters, potentially in the form of loosely organized
MCSs, may be ongoing at the start of the period across eastern
portions of the central Plains toward the central MS Valley region.
These storms will be supported at the terminus of a 30+ kt low-level
jet, accompanied by a marginal severe hail/wind threat. Airmass
modification behind the initial storms will be modest and gradual
due to lingering clouds and precipitation, limiting instability
later during the afternoon. Nonetheless, the passage of the upper
trough atop a southward-sagging baroclinic zone may serve as a focus
for some renewed convective development by late afternoon. Given
modest instability (relatively poor mid-level lapse rates fostering
500-1500 J/kg MUCAPE - most of which may be elevated), later severe
potential should not be widespread. Nonetheless, given elongated
hodographs (and 40-50 kts of effective bulk/speed shear)
multicellular storms (and perhaps a brief, transient supercell) are
possible by late afternoon, with a couple of severe gusts/large hail
stones possible.
...Upper Hudson Valley...
Adequate surface heating of a moist boundary layer will support
surface temperatures warming well into the 70s F amid mid to upper
60s F dewpoints, resulting in MLCAPE over 1000 J/kg (perhaps
approaching 2000 J/kg in spots). The combination of weak ascent
associated with the surface lee trough and insolation will support
the initiation of scattered thunderstorms by early afternoon.
Deep-layer shear should not be overly strong, though point forecast
soundings suggest modest hodograph elongation, especially closer to
the international border. As such, a few longer lived multicells and
pulse single-cells may organize, capable of supporting wet
downbursts, a couple of which may approach severe limits. As such,
damaging gusts may accompany the stronger storms, warranting the
introduction of Category 1/Marginal risk-driven wind probabilities.
..Squitieri.. 07/06/2023
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