SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1137 PM CST Thu Dec 31 2020

Valid 011200Z - 021200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF THE SOUTHEASTERN STATES...

...SUMMARY...
Thunderstorms may pose a modest risk for locally strong gusts and
perhaps a tornado or two over a portion of the Southeast States
today.

...Southeast States...

Shortwave trough will be situated over eastern OK at the start of
this period and this feature will continue northeast into southern
IL by early evening. By 12Z a weak surface low will be located near
Memphis with trailing cold front extending through eastern MS into
the central Gulf. A warm front will extend east through northern MS
and AL, north central GA and into southern SC. This low will track
northeast and occlude across northern KY by early evening. The warm
front will lift north into Middle TN today where surface dewpoints
will reach the low 60s F, with mid to upper 60s with southward
extent into the Gulf Coast states. Cold air damming across the
western Carolinas will limit northward advance of the warm front in
that region. Despite the moistening boundary layer, warm-sector
instability will remain very marginal due to very weak lapse rates
and widespread low clouds. Similar to Thursday, a significant
limiting factor will result from lack of phasing between the deeper
forcing attending the northeast-ejecting shortwave trough and the
moist warm sector which will remain under the influence of an
expansive mid-upper level dry slot. 

A band of convection including a few thunderstorms will likely be
ongoing across a portion of western and middle TN. This activity
will be embedded within favorable vertical shear profiles for severe
storms including supercells, but updrafts will likely be at least
slightly elevated above a stable near-surface layer. Farther east
and south, additional thunderstorms will be ongoing along the
conveyor belt from Middle TN southward through AL and the FL
Panhandle. This activity will shift slowly east during the day.
While some of this convection may become rooted in the boundary
layer, especially with southward extent through AL, the impinging
dry slot and very marginal thermodynamic environment will probably
limit updraft and storm intensity despite strong vertical shear
profiles. Nevertheless, some of this activity might produce a few
instances of locally strong wind gusts and perhaps a tornado or two
during the day.

..Dial/Squitieri.. 01/01/2021

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