SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0655 AM CST Thu Feb 11 2021

Valid 111300Z - 121200Z


Marginally severe thunderstorms are possible today over portions of
Georgia and South Carolina.

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.

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

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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