SPC Dec 23, 2023 1300 UTC Day 1 Convective Outlook

[NorthGeorgiaWX]

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0649 AM CST Sat Dec 23 2023

Valid 231300Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN HIGH PLAINS...

...SUMMARY...
Isolated severe thunderstorms are possible across parts of the
southern High Plains, mainly this afternoon and evening.

...Synopsis...
In mid/upper levels, phasing of northern and southern streams over
the western CONUS will result in a full-latitude trough by the end
of the period, from east-central MT southward over the central/
southern Rockies to eastern Chihuahua.  This will occur as a
weakening cyclone -- now centered over southern/central AZ -- ejects
northeastward to the central High Plains by 12Z tomorrow, and
weakens considerably.  Meanwhile, a northern-stream shortwave trough
-- evident in moisture-channel imagery over the northern Rockies --
will split, with the southern part digging south-southeastward to
NM, and the northern part evolving to a 500-mb low over east-central
MT by 12Z tomorrow.  Height falls associated with this process will
spread across the Great Plains.  As that occurs, a long, broad fetch
of low-level warm advection and moisture-transport will strengthen,
expand laterally, and shift eastward over the Plains States through
the period.

At the surface, a cold front now moving across the Canadian border
into MT will cross the northern High Plains today, then continue
eastward and southeastward.  Meanwhile, lee troughing over the High
Plains will deepen and be overtaken by the front from north-south. 
By 00Z, the front should extend from the central Dakotas across
western NE to a low over central/east-central CO.  A weaker cold
front -- preceding the southern-stream perturbation -- will emerge
from the southern Rockies, reaching near the lee-trough position
over eastern NM and far west TX around 00Z.  By 12Z, the cold front
should extend from a weak low over northwestern MN, across eastern
SD, southern NE, western KS, to northeastern NM.  A broad wind-shift
zone, representing the remnant southern front and lee trough --
should extend by then from the eastern TX Panhandle southward to
eastern Coahuila. 

...Southern High Plains...
Scattered thunderstorms should develop late this afternoon into
evening, and sweep eastward to northeastward across the outlook
area.  Damaging to locally severe gusts and isolated large hail are
possible.  Within the broad belt of currently sub-15% severe-type
probabilities, wind appears to be a somewhat greater threat than
hail, especially over eastern parts of the outlook, where a squall
line should become the main convective mode.  While a tornado cannot
be ruled out, that threat appears very conditional.

Activity should develop as the plume of large-scale ascent and
low-level convergence (near the southern front and lee trough)
increasingly overlap, and related lift impinges on a moistening,
gradually destabilizing sector from the TX Panhandle across the
Permian Basin and Big Bend regions.  Diurnal/diabatic
destabilization will be restricted by cloud cover, and in some
areas, precip.  Still, positive theta-e advection is expected
throughout the day, underlying cooling temperatures aloft from
mid-afternoon onward.  Resulting weakened MLCINH and increased (but
still modest) lapse rates will boost buoyancy, with 50s F surface
dewpoints over most of the area and near 60 along the Rio Grande
just upstream from DRT.  This should support MLCAPE ranging from
around 1000 J/kg in the Big Bend area to 300-500 J/kg over the
southern Panhandle and South Plains regions.  

Low-level and deep shear will favor early-stage supercell potential,
though pronounced weaknesses should be noted in hodographs between
1-3 km.  Effective-shear magnitudes of 40-50 kt should become common
in the immediate preconvective environment.  Upscale development
into a QLCS is likely before the activity outruns its supporting
plume of favorable surface-based buoyancy, which will be narrow in
east-west extent.  While elevated thunderstorms may persist for some
distance eastward, a combination of more-stable near-surface air and
messier, more-linear convective mode will reduce the severe threat
with eastward extent into northwest through west-central TX  and
western OK tonight.  Still, slightly more room has been allotted on
the eastern rim of the outlook for this transition to occur.

..Edwards/Broyles.. 12/23/2023

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