SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1149 PM CST Wed Nov 25 2020

Valid 261200Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
FAR EASTERN TEXAS INTO LOUISIANA...

...SUMMARY...
Isolated large hail may occur with thunderstorms that develop across
parts of far eastern Texas into Louisiana tonight into early Friday
morning.

...Synopsis...
A compact mid-level shortwave trough will move across the Northeast
and eject into the Atlantic while modest surface lee troughing will
prevail along the East Coast through the day into early Friday
morning. Adequate moisture and lift associated with this lee
troughing will promote at least isolated thunderstorm development.
Meanwhile, a second trough aloft is poised to traverse the
Inter-mountain West while diverging from the broader upper cyclonic
flow regime and evolving into a 500 mb cutoff-low. At the surface, a
cold front will move across the Plains states, preceded by a region
of weak low pressure and associated low-level WAA across the
mid-South. Colder mid-level temperatures associated with the
approaching upper trough/cyclonic flow regime will contribute to
enough buoyancy to support a very isolated severe threat early
Friday morning.

...Portions of the mid Atlantic into the Carolinas...
As the aforementioned trough moves toward the Atlantic, a gradual
veering and weakening of the tropospheric wind profiles is likely.
Marginal instability will be in place to support isolated to
potentially scattered thunderstorm development, with strong enough
diurnal heating likely to promote some boundary-layer mixing.
However, the lack of both stronger buoyancy and flow aloft to be
transported to the surface suggests that severe gusts would be too
sparse for Marginal highlights at this time. Nonetheless, a strong
to marginally severe gust or two cannot be completely ruled out.

...Far eastern Texas into Louisiana...
Within the roughly 06-12Z time frame, a plume of steeper mid-level
lapse rates (up to 8 C/km based on 00Z NAM, GFS, and 03Z RAP
forecast soundings) is expected to overspread a modest
moist/warm-air advection regime, promoting over 1000 J/kg MUCAPE in
spots. While much of this instability is expected to be elevated,
cellular convection may ingest air-parcels down to 850 mb, within a
layer of modestly veering low-level winds, with around 150 m2/s2
effective SRH available to any storms that form. As such, storms may
become organized and long-lived enough to support isolated large
hail, with a Marginal risk for severe storms maintained over the
area.

..Squitieri.. 11/26/2020

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