SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0646 AM CST Tue Feb 16 2021

Valid 161300Z - 171200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
SOUTH FLORIDA...

...SUMMARY...
Isolated, marginally severe thunderstorms are possible through
midday over parts of south Florida.

...Synopsis...
A mid/upper-level longwave trough over the central CONUS is
anchoring a large belt of cyclonic flow that covers most of the
CONUS outside the Northeast.  An embedded/leading trough --
initially located from Lake Michigan to the Mid-South -- is forecast
to deamplify considerably and eject across New England around 06Z. 
A trailing trough -- evident in moisture-channel imagery over NV --
should strengthen and dig southeastward to the southern High Plains,
Permian Basin, and parts of northern MX by 12Z tomorrow, near the
broader-scale mean trough position.

At the surface, the main synoptic low was analyzed over extreme
western NY, with occluded front arching into another low near NYC,
just northwest of the triple point.  The associated cold front was
offshore from the Carolinas, then southwestward over east-central/
southwestern FL near a MLB-FMY line.  This front is forecast to move
slowly southeastward across the remainder of the Fl Peninsula
through 00Z.

...South FL...
Widely scattered thunderstorms are expected to move northeastward
from the Gulf and FL Bay/10,000 Islands region across the outlook
area, along/ahead of the cold front, into the afternoon.  Damaging
to marginally severe gusts may occur from the most intense cells,
and a brief tornado cannot be ruled out.

A richly moist low-level air mass -- with surface dew points low/mid
70s F -- is supporting MLCAPE to near 1500 J/kg in the 12Z MFL
sounding.  A shallow but strong "CAPE robber" stable layer near 600
mb may limit coverage of deepest convection ahead of the front, but
also was not evident upshear at Key West.  That RAOB, and VWP from
the WSR-88D several miles to the south-southwest, show an
erratically shaped low-level hodograph with around 100-150 J/kg
effective SRH.  Hodographs may be slightly larger in the unsampled
area to the north and west across the central/northern Everglades,
where a small supercell has been observed in the past few hours. 
Still, in the absence of any upper support for better organization
of the kinematic profile, low-level shear is expected to be at peak
now and remain marginal for another couple hours, then weaken
gradually through mid-afternoon in the shrinking warm sector, with
surface flow veering toward southwesterly.

..Edwards/Smith.. 02/16/2021

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