Day 1 Severe Weather Outlook

Valid 101300Z – 111200Z


Widespread severe thunderstorms are likely across the southern Great
Plains, mainly this afternoon and evening, spreading east into the
Lower Mississippi Valley tonight. The most dangerous corridor for
strong tornadoes and intense damaging winds should be centered on
northeast Texas through northern Louisiana and southern Arkansas
this evening through the overnight.

…South-Central States…
An outbreak of severe thunderstorms is possible later today through
tonight, with the most dangerous portion being tonight into early
Saturday morning with a potential derecho and embedded strong
tornado risk. Primary changes this outlook are to expand the
Moderate Risk east across the Lower MS Valley and increase tornado
probabilities for the evening/overnight period.

Vigorous shortwave trough near the AZ/NM border will shift east
across the southern Great Plains through 12Z Saturday. A powerful
90 kt jet at 500 mb is expected to emanate out of the base of the
trough across east TX/OK. In response to this trough, the LLJ will
increase throughout the period, more notably late in the period.
Along the northwest periphery of low-level moisture advancement,
multiple elevated supercells are expected to develop this morning
across parts of western/northern OK into southern KS. A large hail
risk is anticipated initially, but convection will have an
opportunity to become surface based towards midday, though discrete
cells should not be particularly common as a polar front sags into
this region.

Farther south, strong boundary-layer heating is expected across west
TX where 0-3 km lapse rates are forecast to approach 9 C/km. At the
same time, strong mid-level height falls will spread across the
Pacific cold front/dryline by peak heating, and thunderstorms should
easily develop along the eastern edge of this steeper lapse-rate
plume. Scattered supercells will evolve from east-central OK to
north-central TX by 19-21Z, and farther south into south-central TX
during the late afternoon. This activity will be strongly sheared
and could produce very large hail early in the convective cycle.
With time, multi-scale forcing will encourage consolidation into an
extensive QLCS that should accelerate toward the Ark-La-Tex region
during the evening. Damaging winds will likely be common along the
QLCS with embedded mesovortex and supercell tornadoes.

Guidance such as the 00Z HRW-NSSL and HRW-ARW, along with the 06Z
NAM and 11Z HRRR suggest that pre-frontal convection should develop
out ahead of the QLCS across the Sabine Valley towards 06Z. As this
convection spreads northeast across northern LA towards the
Ark-La-Miss, the strong tornado potential should increase amid
strengthening 0-1 km SRH of 300 m2/s2 and upper 60s surface dew
points. A couple long-track tornadoes are possible given fast storm
motions but convective mode should be messy. Consolidation with the
accelerating upstream QLCS should eventually occur, sustaining
potential for widespread damaging winds with embedded significant
severe gusts and tornadoes as it spreads toward the Lower MS Valley
through 12Z.

..Grams/Mosier.. 01/10/2020


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