Day 1 Severe Weather Outlook

Valid 141300Z – 151200Z


A marginal severe-thunderstorm risk for strong to severe storms
exists for a few more hours over a strip of the central Florida

In mid/upper levels, two primary synoptic- to subsynoptic-scale
troughs will affect the CONUS through the period. Between them,
flow will back from west-northwesterly to westerly and
west-southwesterly, as they evolve in the following ways:
1. The leading trough — currently with shortwave vorticity
components over MO/AR and the southern Appalachians — is forecast
to pivot northeastward to southern QC, across New England, and
offshore from the Mid-Atlantic region. This will occur as the two
components gradually phase/merge.
2. The trailing perturbation — now offshore from the Pacific
Northwest — will amplify through the period as it digs
southeastward across northern CA and OR to NV and southern CA. By
12Z, associated cyclonic flow should cover the southwestern CONUS
from the southern Rockies to the Pacific Coast, as well as parts of
northern Baja and Sonora.

At the surface, a strengthening cyclone — analyzed at 11Z over the
Delaware Bay region — should move northeastward from NJ through the
morning. The cyclone is forecast to continue expanding/deepening as
it moves to southern QC this evening. The associated cold front was
drawn southwestward across northern FL and the northeastern Gulf.
This front should move across the remainder of the FL Peninsula and
Keys before 06Z.

…Central FL…
A loosely organized band of convection, with widely scattered
embedded thunderstorms, will continue to move eastward across the
central FL Peninsula for a few more hours, offering isolated
wind-damage potential. While a tornado still cannot be ruled out,
the threat appears to be diminishing gradually as prefrontal surface
winds veer, increasingly removed from the deepening surface low over
NJ. The air mass across the region will be characterized by surface
dew points upper 60s to low 70s F, with 1000-2000 J/kg MLCAPE
derived from modified 12Z RAOBs and model soundings. Deep shear
will weaken with southward extent and time in the warm sector, but
still remains favorable in the near term, with effective-shear
magnitudes 40-50 kt. However, messy/quasi-linear convective mode,
and the prospect of weakening large-scale and convective lift over
time, indicate the severe threat has become marginal in both
coverage and magnitude.

..Edwards/Broyles.. 12/14/2019


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