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SPC Jan 9, 2024 1300 UTC Day 1 Convective Outlook

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SPC 1300Z Day 1 Outlook
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0658 AM CST Tue Jan 09 2024

Valid 091300Z - 101200Z


Tornadoes (some strong), damaging to severe gusts and isolated hail
are expected over parts of the Southeast, from the eastern Gulf
Coast to the coastal Carolinas.

The main mid/upper-level feature for this forecast will be a well-
developed cyclone, initially centered over the KS/OK/MO tri-state
region, along a synoptic-scale trough extending from MN to the
Arklatex to near BRO.  The 500-mb low is expected to move
northeastward through the period, reaching to near HUF by 00Z and
over southern ON late tonight.  Meanwhile, the trailing trough will
become more neutrally to slightly positively tilted, crossing AL
around 00Z and moving offshore from NC around 12Z tomorrow.

At the surface, a low was analyzed at 11Z near STL, with occluded
front southeastward into AL, and cold front across southern AL, the
western FL Panhandle, and the north-central Gulf.  A warm front was
drawn from south-central AL southeastward over the northeastern
Gulf, then diffusely eastward over central FL and adjoining parts of
the Atlantic.  The warm front may shift/redevelop quickly northward
today into northern FL and parts of GA, as well as reaching the
Carolinas during the afternoon.  The low should move erratically
northeastward to southern Lake Michigan by 00Z, becoming more deeply
occluded.  In the meantime today, the cold front should sweep across
much of the Southeast, extending from central/eastern NC south-
southwestward across Atlantic waters to central FL by around 00Z. 
The cold front should continue to be preceded by a well-organized
squall line.

A strong-severe squall line, with embedded bow/LEWP formations and
sporadically tornadic meso/misovortices -- was evident over
southeastern AL and the western FL Panhandle.  Isolated supercells
ahead of the line this morning, in the FL Panhandle and eventually
into portions of southwestern GA -- will pose a tornado, wind and
isolated severe-hail threat as well.  Even for relatively short-
lived tornadoes, fast translation can lengthen paths more than
usual, and enhance potential damage intensity on one side to
significant (EF2+) level.  For more detailed near-term coverage, see
SPC tornado watch 4 and associated mesoscale discussions.

The main convective band should continue to produce damaging wind
and occasional QLCS tornadoes as it moves eastward over the outlook
area today.  A relative min in forcing for discrete, warm-sector
supercells, as well as in upstream boundary-layer theta-e available
to the squall line, remain plausible, and account for a somewhat
lower (but still well worth outlook coverage) all-hazard severe
threat between the northeast Gulf Coast and Carolinas areas.  Then
potential is expected to ramp up again this afternoon into early
evening as the activity nears the Atlantic Coast, and as warm/moist
advection from a modifying Atlantic boundary layer supports
increasing potential for oceanic supercells to reach the shore
there.  Warm-sector MLCAPE should reach the 1000-1500 J/kg range the
next few hours in the FL Panhandle, and mid/late afternoon over
portions of the coastal Carolinas and west-central/central FL. 
Otherwise, MLCAPE of 200-700 J/kg should be common over most of the
outlook area just ahead of the QLCS.

Vertical shear, by almost any common measure, will remain strong
area-wide.  50-60-kt effective-shear magnitudes should be common,
along with 35-50 kt vectors in the lowest km.  Mass response to the
progressive mid/upper cyclone and trough will continue to yield a
65-95-kt LLJ shifting east-northeastward across the preceding warm
sector.  This will contribute to effective SRH over 400 J/kg in the
warm-frontal zone, and 200-500 J/kg in the warm sector.  In addition
to enlarging low-level hodographs, LLJ-associated momentum transfer
from the intense winds just above the surface, in strong convective
cores, may yield locally severe downdraft gusts, some perhaps
reaching 65 kt.

..Edwards/Bentley.. 01/09/2024

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