SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0745 AM CDT Thu Oct 08 2020

Valid 081300Z - 091200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN PARTS OF
NEAR-COASTAL SOUTHERN LOUISIANA...

...SUMMARY...
A tornado is possible over near-coastal southern Louisiana late
overnight.

...Synopsis...
In mid/upper levels, the northern-stream pattern is becoming more
zonal following the departure of a strong shortwave trough from New
England across the Canadian Maritimes.  Meanwhile, a vorticity max
-- evident in moisture-channel imagery over west-central OK -- is
forecast to move slowly northeastward to the OK/KS/MO border area by
the end of the period, with trough southwestward across west-
central/southwest TX.  As that occurs, Hurricane Delta is forecast
by NHC to turn northward across the western Gulf this period, toward
a mid-period day-2 landfall along the southwestern LA coastline. 
See latest NHC advisories for specific track/intensity forecasts and
tropical watches and warnings related to Delta.

...Southern LA...
A tornado may occur the last few hours of the period from
outer-fringe convection associated with Hurricane Delta.  This is a
marginal and conditional outlook predicated on:
1.  Latest NHC forecasts of track, speed and expansion of the
supportive wind fields, juxtaposed with
2.  Most probable outer reach of favorable, discrete to semi-
discrete convective modes that could become supercellular amidst
enlarging hodographs, and
3.  Favorable inland migration of a maritime/tropical boundary layer
that, based on modified forecast soundings from several models,
would contain theta-e large enough to offset warm temperatures aloft
and yield surface-based buoyant parcels.

Such conditions are expected to spread well inland and include the
diurnal-destabilization period Friday/day-2, but marginally may
spread as far north as roughly I-10 by the 12Z ending time of this
outlook period.  Low-level shear and buoyancy each are expected to
diminish with inland extent overnight, even as they gradually
increase in an absolute sense at any given spot with Delta's
approach.

..Edwards/Goss.. 10/08/2020

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