SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0637 AM CST Wed Nov 11 2020

Valid 111300Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
WESTERN/CENTRAL FLORIDA PENINSULA....

...SUMMARY...
A few tornadoes are possible across parts of Florida mainly
northeast through southeast of the center of Tropical Storm Eta.

...Synopsis...
In mid/upper levels, broadly cyclonic flow will shift eastward
across the western/central CONUS and over the Great Lakes through
the period, traversed by a series of shortwaves and vorticity
maxima.  Weak but broad height falls are expected across the Ohio
Valley and the Southeast.  As that occurs, T.S. Eta should continue
to recurve northward then northeastward toward west-central/
northwest FL.  See NHC advisories for latest tropical watches/
warnings and track/intensity guidance on Eta. A surface cold front
-- initially over OH, western TN and south TX -- will proceed
eastward across most of the Northeast through the period, as well as
the central/southern Appalachians and north-central Gulf west of
Eta.

...FL...
The tornado threat from Eta has increased since the last outlook,
and probabilities are being introduced accordingly across the
peninsula, except for the southeast and far northern parts.  Eta has
become a strong tropical storm and may strengthen to a hurricane as
it obliquely approaches the west-central/northwest peninsular
coastline, based on NHC statements and forecasts.  The projected
track and wind structure will spread favorable low-level shear/
hodographs from southwestern FL across western/central FL through
the period, approximately in step with the translational motion of
the cyclone.  Ambient deep-tropospheric shear (in the 850-200-mb
layer) is forecast to strengthen as well.  The main question,
especially with northeastward/northward extent tonight, will be
instability, so for now potential appears maximized over the
5%/slight area.

A few mini-supercells already have been observed the past several
hours over FL Bay moving northwestward near the southwest coast. 
Despite:
1.  A dearth of surface and upper-air observations between EYW-SRQ,
and
2.  Untested validity of topical-cyclone wind fields in middle-inner
regions by models like the RAP that feed objective-analysis
fields...
The presence of such convective behavior itself reveals an outer rim
of supportive effective SRH, between the already somewhat favorable
VAD wind profiles at the TBW/BYX radars.  The potential for more
such supercells to develop will shift northeastward with time, and
theta-e advection/moisture transport inland across western/central
FL may gradually destabilize the boundary layer between heavy-precip
areas.

Substantial destabilization becomes more uncertain with
northeastward/northward extent overnight across central FL toward
areas just inland from the Atlantic Coast and roughly north of I-4,
because of the offsetting factor of extensive/persistent precip over
an antecedent air mass with weak lapse rates aloft and near the
surface.

..Edwards/Kerr.. 11/11/2020

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