Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Fri May 28 2021
Valid 281300Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEST TO CENTRAL TX
AND EASTERN NM...
...SUMMARY...
Scattered severe thunderstorms with very large hail, damaging winds,
and a couple tornadoes are possible across parts of west and central
Texas into eastern New Mexico, mainly this afternoon and evening.
...TX and eastern NM...
Elevated convection rooted along the low-level baroclinic zone in
northwest TX may pose a risk for isolated severe hail and strong
wind gusts this morning. To the southeast of this activity, a
separate area of thunderstorm development is expected towards midday
near the Big Country/Concho Valley vicinity as convergence
strengthens along the remnant outflow boundary from decaying
convection over east TX. Scattered thunderstorms should also develop
across the higher terrain of eastern NM and the TX Trans-Pecos
during the afternoon.
A plume of moderate to large buoyancy is expected along and south of
the composite front/outflow with peak MLCAPE of 3000-3500 J/kg in
the Edwards Plateau to Permian Basin vicinity of west TX. With a
belt of 30-40 kt 500-mb westerlies atop weak low-level easterlies, a
nearly straight-line hodograph should foster left and
right-splitting supercells capable of producing very large hail.
Some guidance such as the HRRR indicates potential for numerous
supercells across the region by late afternoon which should evolve
into multiple east-southeast propagating clusters this evening,
aiding in an increasing severe wind threat as well. For these
reasons, have expanded the cat 2/SLGT risk. Greatest tornado
potential will probably be maximized along a narrow portion of the
baroclinic zone across the Permian Basin if a discrete supercell is
able to be sustained off the Sacramento Mountains, with spatial
extent likely limited by increasing MLCIN deeper into the
post-frontal air mass.
...Deep South to OH Valley to the Lower Mid-Atlantic...
Ahead of convective outflow associated with decaying convection
across the Deep South to TN Valley and within a broad low-level
moist advection regime, weak surface-based buoyancy is expected this
afternoon. The most deeply mixed boundary layer is expected farther
east along the South Atlantic Coastal Plain where buoyancy should be
lacking due to a hot but dry air mass.
Forcing for ascent should be greatest across a portion of the OH
Valley towards the central Appalachians downstream of a shortwave
trough moving east over the Midwest. But confidence is low that
appreciable destabilization will occur here given pervasive morning
cloud coverage. A separate corridor of ascent may be focused near a
diurnally strengthening surface cyclone in south-central to
southeast VA. Vast differences in the degree of destabilization
among guidance amid poor mid-level lapse rates in regional 12Z
soundings render low confidence in a greater damaging wind threat
here relative to the rest of the lower-end severe risk. Still, a
brief tornado and locally damaging winds are possible along the warm
front from southeast VA into southern MD.
...Northeast WY/southeast MT...
Within a weakly buoyant but amply sheared environment, a couple
discrete supercells may develop off the Big Horns during the late
afternoon to early evening. Here, weak mid-level height falls
downstream of a Northwest short wave trough will be favorably timed
with peak diurnal heating. Isolated large hail and severe wind gusts
are possible until convection weakens upon encountering a more
stable air mass in the western Dakotas.
..Grams/Gleason.. 05/28/2021
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