SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0248 PM CDT Wed Apr 14 2021

Valid 142000Z - 151200Z


Large hail and isolated damaging winds will be possible this
afternoon/evening across the coastal plain of southwest Louisiana
and the middle-upper Texas coast.

...20Z Update...

...Northwest Gulf coast through early tonight...
Storm coverage is expected to continue increasing along the TX
Coastal Plain this afternoon. The environment is characterized by
strong buoyancy and moderate vertical shear, supporting the
potential for strong to severe thunderstorms. Primary severe threat
is large hail and damaging wind gusts, and Severe Thunderstorm Watch
95 was recently issued to address these threats. Thunderstorms will
likely persist in this area through this evening when the loss of
diurnal heating leads to gradually diminishing strength and

Elsewhere across the region (i.e. southern LA), a strong storm or
two may be possible over the next few hours.

...Southern VA/northern NC late this afternoon/evening...
A few strong to severe thunderstorms are still possible this
afternoon and evening across the region amid modest destabilization
and moderate vertical shear. Limited buoyancy will likely keep most
storms from becoming severe but a few supercells capable of damaging
wind gusts and/or hail may develop.

..Mosier.. 04/14/2021

.PREV DISCUSSION... /ISSUED 1121 AM CDT Wed Apr 14 2021/

...Northwest Gulf coast through early tonight...
Widespread elevated convection has been ongoing over LA through the
morning, to the northeast of a rain-reinforced outflow/effective
front just inland from the LA coast.  The convection is linked to
low-level warm advection and a subtle midlevel perturbation now
approaching the Sabine River.  The 12z LCH sounding revealed MUCAPE
greater than 2500 J/kg, though buoyancy decreases with northeastward
extent away from the boundary, and as a result of substantial
convective overturning.  The greater threat for a few severe storms
should be focused along the surface boundary (near the
southwest/south central LA coast), where another cluster of storms
is expected, which will likely keep the boundary near the coast. 
Occasional large hail and/or damaging gusts will be possible with
the stronger embedded storms/supercells through the day.

Farther west along the TX coastal plain, 12z soundings reveal that
low-level moisture depth has increased and cap strength has
decreased over the past 12-24 hours.  Lapse rates above the 700 mb
level remain quite steep (> 8 C/km), and boundary-layer dewpoints of
72-74 F are driving MLCAPE of 2500-3000 J/kg.  Given the weakened
cap and the approaching of another subtle midlevel perturbation (now
south of the Big Bend), the chance for surface-based storms has
increased along a slow-moving front this afternoon/evening. 
Assuming a few storms form along the middle and upper TX coastal
plain, the large CAPE and effective bulk shear of 30-40 kt will
support a mix of organized clusters and supercells capable of
producing large hail and damaging winds.

...Southern VA/northern NC late this afternoon/evening...
A subtle shortwave trough now over western KY/TN will progress
eastward toward VA/NC by this evening, around the southeastern
periphery of the midlevel low over the upper Great Lakes.  A weak
surface cyclone is expected to form across the Piedmont in advance
of the midlevel trough, and then move eastward through this evening.
Modest low-level moisture return across NC into southern VA
(boundary-layer dewpoints now in the mid 50s) and afternoon
temperatures of 75-80 F will contribute to some destabilization this
afternoon.  However, there is uncertainty regarding how much
vertical mixing will offset moisture advection and limit buoyancy. 
Even with just a few hundred J/kg of MLCAPE, long hodographs with
some low-level curvature will support a threat for somewhat
high-based/low-topped supercells capable of producing a few damaging
gusts and marginally severe hail for a few hours late this

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