Day 1 Severe Weather Outlook

Valid 201300Z – 211200Z

…NO THUNDERSTORM AREAS FORECAST…

…SUMMARY…
Thunderstorm areas are not expected over the contiguous U.S. today
and tonight.

…Synopsis…
A rather highly amplified, yet still progressive, upper-air pattern
will prevail over the CONUS this period. A strong shortwave trough
— now located over eastern SD, southern MN and WI — will dig
southeastward across the mid Mississippi and Tennessee Valley
through the period, while gradually intensifying. By 12Z, a closed,
elongated, positively tilted 500-mb cyclone should develop along
this trough over northern GA and vicinity. Upstream, a high-
amplitude ridge will shift eastward from the Rockies across the
Great Plains. Associated low-level frontal passages have rendered
the inland boundary layer too cold, dry and/or stable to support
deep convection over land.

Behind that, heights will fall across much of the West as a series
of perturbations approaches and/or moves inland from the Pacific.
The strongest such feature is a cyclone whose center is apparent in
moisture-channel imagery near 44N141W. As this vortex approaches
the Pacific Northwest, it will assume a more-negative tilt, with a
basal shortwave trough/vorticity banner approaching the OR coastline
at 12Z. This feature will be preceded by a lengthy fetch of
low-level warm advection and a baroclinic cloud/precip band, but
with time series of forecast soundings reasonably showing lapse
rates in ideal icing layers too stable to support thunder potential.
While a lightning strike cannot be ruled out in the last few hours
of the period, in the eastern edge of the colder air aloft preceding
the cyclone, potential appears too isolated to justify an outlook
area.

..Edwards.. 01/20/2020

$$

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