SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0655 AM CST Thu Feb 11 2021 Valid 111300Z - 121200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF GEORGIA AND SOUTH CAROLINA... ...SUMMARY... Marginally severe thunderstorms are possible today over portions of Georgia and South Carolina. ...Synopsis... In mid/upper levels, a binary cyclone was prominent in moisture- channel imagery over central Canada, with circulation centers evident over far northwestern ON and southern SK. Through the period, their Fujiwhara interaction will lead to vortex consolidation, with largely combined gyre centered over southern MB by 12Z tomorrow. As that occurs, a belt of zonal to subtly cyclonic flow will cover most of the CONUS east of the Rockies and north of about 35N. A southern-stream synoptic trough was apparent from the San Juan Mountains of CO across northwestern mainland MX to southern Baja. This perturbation will shift east-southeastward through the period, reaching west-central TX, Coahuila and the central Pacific Coast of MX by 12Z. Numerous small, horizontally stretching vorticity lobes (some convectively enhanced) will traverse the confluent-flow belt that extends downstream across much of the main body of TX and the Southeastern States. At the surface, 11Z analysis showed a wavy, slow-moving front from a weak low over south-central LA northeastward across AL near BHM, splitting into two branches: one extending northeastward through a weak low near TRI, another being a warm front moving slowly northward over northern GA and southern SC. Another weak low may develop in the next few hours over northern AL and ripple northeastward along the merger point of the two frontal branches, toward northwestern SC. The trailing front will move southeastward across the remainder of MS, almost all of LA, and roughly the northwestern 1/2 of AL by 00Z. The eastern part of the baroclinic zone should settle across north-central GA into western/central SC through the afternoon, with some influence by convective outflow. ...GA/SC... Scattered thunderstorms near the front will cross the outlook area this afternoon into early evening, offering isolated damaging gusts. A tornado cannot be ruled out, but that threat appears very low and conditional. A narrow plume of airmass recovery is expected across the outlook area, related to both warm advection and modest diurnal heating there and upstream. The northeastern rim of weak surface-based buoyancy will extend under the southern fringe of favorably strong mid/upper winds. Only weakly convection-supporting lapse rates will limit absolute MLCAPE amount (generally 500 J/kg or less) and keep CAPE density low. As such, the severe-hail threat appears minimal this far east. However, small/embedded bowing structures and at least transient supercells are possible, contributing to a low-end wind threat. A brief tornado is possible with any surface-based supercell that can interact with locally enriched boundary-layer vorticity/SRH in the baroclinic zone. Low-level SRH/vorticity and lift all will be modest in the warm sector due to relatively weak and veered near-surface winds, with attendant modest hodograph size. Instability will diminish quickly northward past the front, and eastward past favorable low-level theta-e. As such, the marginal unconditional severe threat appears fairly tightly confined to near the boundary, and the outlook area has been slightly reshaped accordingly. ..Edwards/Dial.. 02/11/2021
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