Day 1 Severe Weather Outlook

Valid 222000Z – 231200Z

…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FLORIDA
KEYS AND ADJACENT SOUTH FLORIDA…

…SUMMARY…
A tornado or two and isolated damaging winds will be possible
through this evening across the Florida Keys and overnight across
southeast Florida.

Showers and thunderstorms in the vicinity of the western FL Keys
have exhibited transient rotation this afternoon, albeit with little
to no lightning thus far. Reference Mesoscale Discussion 2227 for
the latest short-term thinking in this area.

An increase in thunderstorms is anticipated this evening and
overnight across the FL Keys/adjacent south FL as the cold front and
associated forcing for ascent approaches the area. RAP Forecast
soundings continue to show curved/lengthening hodographs tonight
with surface-based instability of 500 to 1000 J/kg, supporting
supercell structures and low-level rotation with the strongest
storms. A tornado or two will be possible in addition to isolated
damaging winds.

..Bunting.. 12/22/2019

.PREV DISCUSSION… /ISSUED 1013 AM CST Sun Dec 22 2019/

…FL Keys this afternoon into southeast FL tonight…
A midlevel low over the lower MS Valley will move slowly
east-southeastward to the northeast Gulf coast by early Monday. An
associated surface low will move inland over the FL Panhandle and
continue generally eastward near the FL/GA border to the Atlantic
coast by Monday morning, as a trailing cold front progresses
eastward across the FL peninsula. Within the warm sector of the
cyclone, regional 12z soundings revealed poor lapse rates aloft and
moist profiles across central/north FL, which will limit the
potential for severe storms this far north. The richest low-level
moisture (low 70s boundary-layer dewpoints) and resultant buoyancy
will overspread the FL Keys this afternoon and southeast FL tonight.

Modest forcing for ascent and the moist profiles will favor a mix of
cells and clusters as the primary convective modes. MLCAPE of
500-1000 J/kg, with effective bulk shear of 40 kt or greater and 0-1
km SRH of 150-200 m2/s2, will support a threat for embedded
supercells capable of producing a tornado or two and isolated
damaging winds. Small supercells in the warm advection regime will
pose a marginal tornado/damaging wind threat through early-mid
afternoon near Key West. The primary severe threat is expected this
evening across the Keys and into southeast FL overnight, immediately
in advance of the surface cold front.

$$

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