Day 1 Severe Weather Outlook

Valid 231300Z – 241200Z


Severe thunderstorms are not forecast across the contiguous United
States today.

A highly amplified and progressive upper-air pattern will continue
across the CONUS this period, dominated by a major synoptic trough
shifting eastward over the central part of this nation. Initially,
two primary shortwave troughs were evident, with an axis connecting
them defining the larger-scale trough:

1. A basal perturbation over east-central OK, north-central/
northeast TX and the upper TX Coast. This feature will phase with a
minor, trailing shortwave trough over southwest TX. The combined
shortwave trough will pivot eastward to portions of MS and
southeastern LA by 00Z, then eject northeastward across the southern
Appalachians, effectively dissipating by 12Z. This will occur
amidst strong height falls and intensifying winds aloft related to
the next/stronger perturbation…

2. An initially negatively tilted shortwave trough extends from
western ND to southwestern KS. The southern vorticity lobe of this
trough is forecast to organize rapidly into a closed 500-mb cyclone
today, its center reaching southeastern KS by 00Z. The cyclone will
deepen and expand further, reinforcing the synoptic trough. By the
end of the period, the associated low should reach the MO Bootheel
area, with troughing roughly over the Mississippi Valley from MN-LA.

Elsewhere, a shortwave trough — apparent in moisture-channel
imagery over the northeastern Pacific near 140W — will move ashore
over the OR/WA coasts late in the period, around 09-12Z. A
combination of large-scale vertical motion from DCVA and the
left-exit region of a cyclonically curved upper jet streak will
steepen lapse rates over the marine layer ahead of the trough in
support of isolated, overnight, near-shore thunder.

At the surface, 11Z analysis showed a broad, weak cyclone over
southeast TX, with cold front southwestward to northeastern MX, and
warm front southeastward across the north-central/east-central Gulf.
The low will remain diffuse as it migrates northeastward and further
inland today, across parts of LA and western/northern MS. Meanwhile
a stronger low related to the strengthening mid/upper-level cyclone
will move from its 11Z position between OMA-FNB to north-central MO.
The warm/marine front will make only slow northeastward progress,
with the boundary layer still modifying to its south as well. By 12Z
the lows will consolidate into a primary synoptic cyclone centered
over central/southern IL, with cold front across middle TN, central
AL, and the central Gulf.

…Gulf Coast States…
Isolated to widely scattered thunderstorms are expected in episodic
fashion, with the potential shifting west to east across the outlook
area through tonight.

A broad sheet of elevated, low-level warm advection and moisture
transport is in place across the region, tilted gently upward with
inland extent. This regime will be reinforced amidst mass response
to the 500-mb cyclone’s developing and deepening along a path from
KS across the Ozarks. While weak boundary-layer-rooted buoyancy may
develop inland in the wake of morning precip/convection, it is
expected to be displaced horizontally from the strongest forcing.
Meanwhile the greatest instability will remain over a modifying
low-level air mass over the open Gulf.

The great majority of inland convection should be elevated atop a
relatively stable boundary layer, amidst modest lapse rates. Brief/
isolated severe cannot be ruled out with nearly surface-based
convection brushing the coastline near the mouth of the Mississippi
River; however, the unconditional/organized potential inland is too
low to warrant a categorical outlook at this time.

..Edwards/Gleason.. 01/23/2020


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