SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0746 AM CDT Thu May 26 2022
Valid 261300Z - 271200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM OHIO TO PARTS
OF SOUTHERN ALABAMA AND THE FLORIDA PANHANDLE...
...SUMMARY...
Isolated to widely scattered severe thunderstorms are possible over
parts of the inland Northwest, and from Ohio Valley region to the
east-central Gulf Coast and southern Appalachians.
...Synopsis...
A pronounced, slowly progressive, deep-layer cyclone was apparent in
moisture-channel imagery over parts of KS, MO, OK, AR, southern IA
and southeastern NE, centered roughly between JLN-TOP. The
accompanying mid/upper-level trough extended southward across the
Arklatex region to the northwestern Gulf. By 00Z, the 500-mb low
should be over eastern MO, with trough roughly southward down the
lower Mississippi Valley and offshore from LA. By 12Z, the low
should reach the lower Wabash River area, with trough
south-southwestward past BIX.
Farther upstream, synoptic-scale ridging will cross the Rocky
Mountain States, ahead of a complex, elongated mid/upper cyclone now
located west of Vancouver Island and south of the Gulf of Alaska.
Associated height falls and southwest flow aloft will spread inland
over the Northwest. Embedded in that flow, a lead shortwave
perturbation -- initially apparent with positive tilt from just west
of the WA coast southwestward to about 600 nm W of SFO, will pivot
inland across WA/OR around 00Z. The trough should weaken somewhat
overnight as it accelerates toward the northern Rockies and the
larger-scale ridge position.
At the surface, 11Z analysis depicted a low near SZL, with cold
front arching across southeastern MO, northwestern MS, and
south-central LA. A warm front was drawn across northern IL,
central Lower MI, and eastern OH, becoming quasistationary while
wrapping around the Appalachians from Western WV to northeastern TN
and northwestern SC. This front extended to another low offshore
from HSE. By 00Z, the cold front should curve from the low near UIN
across southern portions of IL/IN, middle TN, northern/southwestern
AL, to near the mouth of the Mississippi River. By 12Z, it should
reach eastern parts of KY/TN, the FL Panhandle, and the central
Gulf. The eastern front should shift diffusely and slowly northward
across the Carolinas later today.
...Ohio Valley region to Gulf Coast...
Multiple rounds and areas of widely scattered to scattered
thunderstorms are expected across the outlook area today into this
evening -- both in the form of cold-frontal and prefrontal bands
aligned roughly parallel to the cold front, and a blend of discrete
cells and clusters in the weakly capped warm sector. Damaging to
isolated severe gusts, a marginal overall tornado threat, and
isolated severe hail are possible across a large swath from the Gulf
Coast across the Ohio Valley and into the western Carolinas, with
wind likely being the most common severe-report type.
Convective coverage has been increasing gradually the last several
hours near the Gulf Coast -- primarily over water, and may
expand/develop inland with time this morning across AL and the FL
Panhandle. This is occurring near a weak surface low between
BVE-MOB and a related low-level convergence zone, within a richly
moist air mass (low/mid 70s F surface dew points) supporting MLCAPE
in the 1500-2500 J/kg range -- diminishing gradually with
northward/inland extent across MS and western AL. Farther east, a
baroclinic boundary is noted near or just off the FL Panhandle
coastline between PAM and western Apalachee Bay, reinforced by
precip from a complex extending well offshore (and which has
contained occasional supercells appearing to be strengthened by
vorticity in the baroclinic zone). That quasistationary boundary
may limit inland penetration of favorable boundary-layer air in the
near-term. Strongly difluent flow aloft also has been noted,
rendering highly variable effective shear (magnitudes generally
25-50 kt, increasing inland into a currently less-unstable
environment). See tornado watch 274 and related mesoscale
discussions for more-updated near-term info on this region.
Inland destabilization is expected later this morning into
afternoon, related to both theta-e advection -- recovering west of
the Panhandle/Gulf complex and its dissipated northward extension
over eastern AL and GA. This may support both an inland growth of
the Gulf activity over the next few hours, and later-morning/
afternoon development along/ahead of the front well inland across
the Tennessee/Ohio Valleys. 35-50-kt effective-shear magnitudes
(with shear and mean-wind vectors obliquely off the frontal
alignment) will support mixed convective modes, but mainly linear.
The "slight" areas have been connected accordingly, though a
relative minimum in severe potential still may exist farther east
near the mountains, where effects of the "wedge" front will be more
persistent. Backed low-level winds preceding convection closer to
the low, over IL/IN, also may support some hodograph enlargement,
and marginal tornado probabilities have been expanded into those
areas.
Conditional, mesoscale to localized maxima in tornado potential also
may exist near the Carolinas front (but with considerable
uncertainty related to mode and cross-boundary cell motion), and in
the weaker-instability arc along/ahead of the front over the IL/IN
region. If any of those becomes better-focused and less
conditional, an upgrade in those probabilities may be considered in
a succeeding outlook.
...Interior Northwest...
Isolated to scattered thunderstorms are expected to develop over
western portions of OR/WA and central OR late this afternoon, then
move northeastward into the evening. Meanwhile, the environment
from central/eastern OR and southeastern WA, northeastward across
western/northern ID, will best support severe potential, in the form
of gusts and hail.
Antecedent diurnal heating of lower terrain east of the Cascades
will lead to a deep, well-mixed boundary layer beneath increasing
midlevel moisture. Preconvective lapse rates aloft are expected to
increase as well, related to large-scale DCVA/ascent preceding the
shortwave trough. Pockets of MLCAPE near 500 J/kg are possible,
with a broad area exceeding 100 J/kg -- nonetheless extending into
thermal layers suitable for lightning generation. Although low-
level hodograph size and shear-vector magnitudes will be limited by
some westerly to northerly near-surface wind components, favorable
deep shear will exist for either high-based supercells or organized
bowing structures. Any hail associated with the former would be
well-maintained to the surface through the subcloud layer, and large
DCAPE will support the potential for cold pools to aggregate and
produce a wind swath with a northeastward thrust into ID.
..Edwards/Kerr.. 05/26/2022
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