Day 1 Severe Weather Outlook

Valid 201200Z – 211200Z


Severe storms capable of very large hail, a few tornadoes, and
damaging winds are expected over parts of eastern Oklahoma,
northeast Texas and western Arkansas during the evening and through
early Monday morning. Other isolated severe activity is possible
over central Texas and Missouri. Farther east, a severe storm or two
cannot be ruled out over eastern North Carolina during the morning.

An upper trough will amplify as it moves from the Rockies into the
Plains, with substantial height falls. Middle and upper-level winds
will strengthen throughout the period with a leading jet max
becoming better defined overnight from north TX into MO with 500 mb
speeds to 100 kt. In the low levels, 850 mb winds will increase to
50-60 kt ahead of a cold front, extending roughly from eastern KS
into northwest TX at 00Z. Ahead of this front, low-level moisture
will be in the process of surging north, with mid to upper 60s F
dewpoints into north TX by late afternoon. Moisture advection will
increase overnight as a surface low translates northeast across
eastern OK and into MO, leading to rapid destabilization over parts
of OK, AR, and southern MO.

To the east, a weakening shortwave trough and surface low associated
with the remnants of Nestor will enhance shear across the Mid
Atlantic, and may support a severe risk over eastern NC during the

…Northern TX…eastern OK…western Arkansas…
The region will likely be devoid of thunderstorms through late
afternoon as low-level moisture continues to spread north and lapse
rates steepen. By around 00Z, storms are expected to rapidly develop
near the surface trough near central OK, and perhaps into eastern KS
as well where instability will be weaker. Steep lapse rates along
with enlarging hodographs will favor supercells. Effective SRH
increasing to 300-400 m2/s2 over eastern OK and northeast TX during
the evening and deep-layer effective shear over 60 kt will favor
tornadoes and very large hail, assuming cellular storm mode. With
time, CAMs suggest storms merging into an MCS or a series of bows as
forcing become cold-front dominated. Damaging winds are likely, and
will likely spread east into AR.

If the boundary layer destabilizes sufficiently into southern MO,
strong shear will favor QLCS structures along the front with
damaging wind or brief tornado potential. Farther north into eastern
KS and northern MO, elevated instability may prove sufficient for
marginal hail during the evening as elevated moisture advection
interacts with cold temperatures aloft and strong deep-layer shear.

…Eastern NC – early day..
A surface low will move rapidly northeast across eastern NC through
midday, with mid 70s F dewpoints and strong low-level shear along
and east of the track. Warm advection and lift will be most
prominent during the 12-15Z time frame, with widespread rain and a
few thunderstorms ongoing early day. Although the time window of
opportunity is small, the very moist air mass may prove sufficient
for surface based storms near the surface low where SRH would then
become effective to the surface and over 500 m2/s2. If this occurs,
a tornado or damaging wind gust will be possible.

..Jewell/Squitieri.. 10/20/2019


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