611
ACUS01 KWNS 271300
SWODY1
SPC AC 271259

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0759 AM CDT Mon May 27 2024

Valid 271300Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE
ATLANTIC SEABOARD AND NORTH/CENTRAL TX...

...SUMMARY...
Severe thunderstorms are expected today across parts of the lower
Great Lakes, Mid-Atlantic, and Southeast.  More isolated severe
thunderstorms are possible this afternoon and evening across much of
central and east Texas, as well as southwest Oklahoma and the
mid/upper Mississippi Valley.

...Synopsis...
In mid/upper levels, a messy synoptic-scale trough -- accompanied by
several northern- and southern-stream shortwaves and vorticity
maxima -- will proceed eastward across ON, the upper Great Lakes,
and the Ohio/Tennessee Valleys through the period.  A northern-
stream perturbation -- initially extending from Lower MI across N --
should pivot over Lake Huron and the upper Ohio Valley/lower Great
Lakes today.  The southern part should reach central/eastern PA and
central NY by 00Z.  Meanwhile, a strong upstream perturbation -- now
evident in moisture-channel imagery over the Dakotas -- should move
southeastward to southern MN and IA by 00Z, then portions of IN/OH
around the end of the period.  In the southern stream, a positively
tiled shortwave trough -- containing a string of vorticity maxima
(some convectively induced) -- will move eastward over the
southeastern CONUS.

At the surface, a well-occluded low was apparent at 11Z over
northern Lake Michigan, with occluded/cold front arching across
Lower MI, OH, the Ozarks, and north-central to west-central TX.  The
front was preceded over much of the Appalachians, Southeast and
Mid-South by extensive convective outflow.  By 00Z, the front should
reach western/central NY, the central/southern Appalachians, and
central LA, becoming a stationary to slow-moving warm front over
north-central/northwest TX into northern NM.  A dryline -- now
located near a DYS-SJT-SOA line and into northern Coahuila -- should
move only slightly eastward today while becoming more sharply
defined as moisture returns northward, to the south of the frontal
zone.

...Atlantic Seaboard to Southeast...
Ongoing complexes of strong-severe thunderstorms over portions of AL
and GA may produce continued damaging wind -- along with isolated
large hail and/or a tornado -- while moving into a favorably moist
and slowly diurnally destabilizing airmass in their path over GA.
Meanwhile, initially subsevere northeastern parts of the original
MCS that crossed the southern Appalachians also may re-intensify
over the remainder of the morning into midday.  See SPC Severe
Thunderstorm Watches 331-332 and related mesoscale discussions for
near-term details.

Northern parts of this activity -- or additional thunderstorms
developing along the front of the residual pressure and theta-e
perturbations from activity that crossed the Appalachians overnight
-- may result in widely scattered to scattered thunderstorms in
clusters through at least midday over parts of the Carolinas, and
perhaps into southern VA.  Meanwhile, isolated to scattered
strong-severe thunderstorms are expected to develop along/ahead of
the front during midday and through the afternoon from the
Mid-Atlantic into parts of upstate NY.  Overall convective coverage
may increase northward into stronger large-scale lift and
frontal/prefrontal convergence, though low-level moisture will
generally decrease, along with diurnal heating and midlevel lapse
rates.

Surface dewpoints should range from the low/mid 70s across GA and
the Carolinas Piedmont/coastal plain (recovering behind last
evening`s MCS) to the 60s over most of the rest of the outlook
corridor.  Enough veering with height in the boundary layer and
related hodograph curvature exist in forecast soundings --
especially from eastern NC northward -- to support effective SRH in
the 150-300 J/kg range, with supercell potential and some tornado
threat apparent.  Effective-shear magnitudes of 35-45 kt should be
common, contributing to potential for both supercells and organized
multicells in lines or clusters.

...Southern Plains...
Isolated to scattered thunderstorms are possible from north west TX
southeastward across parts of LA and southern MS.  Damaging gusts
and large hail are the greatest concerns.  Within that corridor,
however, a conditional potential exists for isolated supercells
offering large to very large/destructive hail, especially over
north-central and parts of central TX.  Given the large buoyancy
forecast, and favorable deep shear, along with weak MLCINH and
regionally maximized convergence expected with a surface low near
the front/dryline intersection, confidence has increased enough to
introduce unconditional significant-hail probabilities, upon which
the "slight" area is based.

Strong diurnal heating and decreasing EML-related capping with
eastward extent will result in progressively greater convective
potential and denser coverage along/ahead of the front this
afternoon from northwest TX to the central Gulf Coast States.
Surface dewpoints commonly in the 70s F and steep midlevel lapse
rates will support a field of 4000-5000 J/kg MLCAPE over central/
north TX south of the front, decreasing to a still favorable 2500-
3500 J/kg over southern MS.  Veering of winds with height, and a
lengthy hodograph structure well-suited for hail production in any
sustained supercells -- are expected in north-central TX.  Coverage
concerns linger, considering that height rises are forecast across
this region through the period, behind the synoptic trough.

..Edwards/Goss.. 05/27/2024

$$