Day 1 Severe Weather Outlook

Valid 281300Z – 291200Z


Isolated severe storms are possible from eastern Kansas to the
Arklatex and Mid-South regions, most concentrated in and near the
western Ozarks.

The most influential upper-air feature for this forecast will
continue to be a high-amplitude synoptic trough advancing eastward
across the west-central/central CONUS. A basal shortwave trough —
initially located over portions of CO/NM — is forecast to eject
northeastward today, evolving into a closed 500-mb cyclone this
evening and overnight across the central Plains. As this occurs, a
very strong mid/upper-level jet streak (170-180 kt at 250 mb and
85-100 kt at 500 mb) will form this afternoon over portions of
southwest TX to eastern OK, shifting north-northeastward across more
of eastern OK, southeastern KS and MO overnight. Intense low/
middle-level mass response also is expected, with 00Z 850-700-mb
layer flow commonly in the 50-75-kt range across northeastern OK,
eastern KS and southwestern MO.

At the surface, an elongated area of low pressure was evident from
central CO to the TX Panhandle, with weak/primary low over
southeastern CO. The cold front was drawn across the northern/
eastern TX Panhandle, northwest/west-central TX below the Caprock,
then southwestward across the Big Bend area. The primary low is
forecast to shift/redevelop eastward across southern/central KS
through the day, reaching northeastern KS around 00Z. The cold
front then should extend from there across east-central OK and
north-central through southwest TX. Considerable deepening of the
cyclone will occur overnight, with the low reaching the southwestern
MN/northwestern IA area by 12Z. By that time, the cold front should
extend from an occlusion triple point in the eastern IA/northwestern
IL area across southeastern MO, eastern AR, east TX, to near LRD.

…Eastern Kansas to Arklatex/Mid-South…
Scattered to locally numerous thunderstorms are expected to develop
throughout the day near the cold front across parts of south-
central/eastern KS, central/eastern OK and north-central/northeast
TX. A relatively dense, quasi-linear convective mode should
dominate, with embedded or precursory supercells a lower/conditional
threat. As such, the main threat should be damaging winds, with
several severe gusts possible. A conditional threat for tornadoes
also may develop, especially of the embedded/QLCS variety. A
separate corridor of convection may develop this afternoon and
evening in a zone of low-level warm advection over the Mid-South
area, offering a marginal wind threat in minimal near-surface

As the primary/western band of convection shifts eastward — with
individual/embedded elements racing northeastward amidst intense
deep-layer flow — it will encounter a marginally yet sufficiently
destabilizing environment behind morning convection/precip.
Low-level lapse rates should remain only weakly unstable amidst
considerable cloud cover, with only muted surface heating, and the
bulk of destabilization likely coming from warm-sector theta-e
advection. Accordingly modified RAOBs and forecast soundings
suggest peak preconvective MLCAPE generally in the 300-800 J/kg
range over eastern portions of OK/KS. Effective-shear magnitudes in
the 45-60-kt range should be common. Strong low-level shear also is
forecast, but with erratically shaped and rapidly evolving
hodographs, and highly variable SRH.

Buoyancy will decrease eastward and with time tonight across
northern AR and southern/central MO. Weaker convective-scale
forcing and stronger CINH will curtail severe potential southward
from the Arklatex region, while surface-based instability will
diminish considerably with northward extent past about I-70. Those
considerations generally frame the outlook probabilities as drawn.

..Edwards/Smith.. 12/28/2019


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