SUMMARY... Severe thunderstorms with very large to giant hail and damaging winds are expected across parts of southern Texas this afternoon into tonight. Severe storms with occasional large hail will be possible this afternoon across northeast Texas and northwest Louisiana, and a few damaging gusts will also be possible this afternoon/evening across central and eastern North Carolina. ...
20Z Update... ...TX Hill Country/Rio Grande Valley... 17Z DRT sounding sampled very steep mid-level lapse rates and moderate convective inhibition. Since then, temperatures have warmed into the upper 80s with dewpoints remaining in the low 70s. Consequently, much, if not all, of the convective inhibition once in place has now likely eroded. Additionally, the cold front continues to push southward and now arcs from northern Terrell County TX through ECU and eastward through central TX. Visible satellite shows some deep cumulus has developed along this front as well as several blowoffs from attempts at deeper convection. All of these trends suggest eventual convective initiation within this very unstable environment. As mentioned in the previous discussion, supercells capable of producing isolated very large to giant hail (3-4" diameter) and damaging gusts are anticipated. ...Northeast TX to Northwest LA... Ongoing severe storm over Cass and Marion Counties along the TX/LA border has not shown any trend towards weakening thus far. Downstream air mass remains supportive of storm persistence, so the threat for large hail will continue through the afternoon. Additional storm development is possible late this evening amid a strengthening low-level jet. Some hail is possible with these storms as well. ...Central/Eastern NC... Thunderstorm coverage is expected to increase over the next few hours along the cold front moving eastward into central NC. Overall buoyancy will be modest, but effective bulk shear near 30-35 kt will be sufficient for a few organized clusters/supercells capable of producing damaging outflow gusts and marginally severe hail. ..Mosier.. 05/10/2021 .
PREV DISCUSSION... /ISSUED 1129 AM CDT Mon May 10 2021/ ...Rio Grande Valley/south central TX this afternoon/evening... Boundary-layer dewpoints in the low 70s have spread westward across south central TX to the Rio Grande, beneath very steep midlevel lapse rates near 9 C/km. The combination of surface heating in cloud breaks by afternoon, low-level ascent along a stalled front across the Edwards Plateau, and upslope flow into the Serranias Del Burro (west of DRT), will support at least widely-scattered thunderstorm development by mid afternoon. The initial storms should be discrete, with some clustering possible later this evening as a result of cell mergers/interactions of right- and left-moving supercells. MLCAPE near 4000 J/kg and effective bulk shear of 40-50 kt with long hodographs will favor supercells capable of producing isolated very large to giant hail (3-4" diameter) and damaging gusts. Additionally, low-level hodograph curvature/shear may remain sufficient for an isolated tornado late this afternoon/evening. ...
Central/eastern NC this afternoon/evening... A subtle midlevel trough will move over NC this afternoon, as a surface cold front moves southward from VA into NC. Surface heating in cloud breaks will boost afternoon temperatures to near 80 F with boundary-layer dewpoints in the low-mid 60s along and south of the front, resulting in MLCAPE of 500-1000 J/kg this afternoon across NC. Scattered thunderstorm development is expected along and a little south of the front as buoyancy is maximized and convective inhibition is removed by mid afternoon, and storms will subsequently spread east-southeastward across NC through this evening. Though midlevel lapse rates will not be steep, deep-layer vertical shear will be sufficient for a few organized clusters/supercells capable of producing damaging outflow gusts and marginally severe hail. ...
Northeast TX to northwest LA through mid afternoon... Elevated storms formed this morning over the Red River Valley in association with warm advection and a subtle midlevel speed max moving eastward. The storms may persist for a few more hours while moving along the northeast edge of the buoyancy gradient (MUCAPE of 1000-2000 J/kg), given the potential to maintain some organized structures with effective bulk shear near 50 kt for the elevated parcels. Occasional large hail will be the main threat. ...
Southern LA this afternoon... A cluster of storms with occasional bow and embedded supercell structures is now moving across the New Orleans area. The near-storm environment is somewhat favorable for organized storm structures along the residual outflow boundary from overnight convection. However, the storms appear to have peaked in intensity earlier this morning, and the potential for any substantial uptick this afternoon appears too uncertain to warrant any change to the Marginal risk assessment. Read more LIVE: spc.noaa.gov
NWS SPC COnvective Outlook provided by Arlingtoncardinal.com/weather
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