Day 1 Severe Weather Outlook

Valid 051300Z – 061200Z


No severe-thunderstorm areas are forecast across the contiguous U.S.

In mid/upper levels, a longwave trough will be maintained from the
Canadian Arctic islands to the Mississippi Valley through the
period. Associated cyclonic flow will cover most of the CONUS from
the Rockies eastward, with only very minor (at most) embedded
shortwaves moving over areas where deep moist convection is

Farther southwest, a persistent, initially cut-off cyclone is
evident in moisture-channel imagery offshore from northern Baja —
centered near 30N119W. This perturbation is expected to move slowly
northeastward and inland this period, across southern CA, northern
Baja and western AZ. Associated difluent flow in upper levels will
spread over Sonora and northern AZ, with shortwave ridging drifting
eastward across southern NM and far west TX.

At the surface, 11Z analysis showed a wavy frontal zone across
central FL and the north-central Gulf. This boundary will continue
to become more diffuse with time, effectively redeveloping northward
across Atlantic waters offshore from the Carolinas, then
southwestward across the FL/GA line to Gulf shelf waters off TX/LA.
Troughs drawn north of this boundary over the northeastern Gulf and
Atlantic will persist. A cold front was drawn from southeastern ON
across OH and central AR, becoming quasistationary across the
Arklatex and central TX to a weak low over northern Coahuila. This
front should move offshore from New England and the Mid-Atlantic
region through the period, effectively merging with the redeveloped
southern front over the coastal Carolinas/FL/GA region, and
weakening over TX.

…Northern FL and vicinity…
Isolated to widely scattered thunderstorms are possible across much
of the FL Peninsula and southern GA today into tonight. A few
strong cells may develop in a corridor from the east-central
Panhandle to the coastal bend region, eastward across the northern
peninsula. At this time, the severe potential appears too isolated
and uncertain for an unconditional risk area, but hail and/or gusts
approaching severe limits cannot be ruled out from any persistent
cells. This corridor will denote the northern part of a favorably
moist boundary layer (dew points mainly mid/upper 60s F, locally
near 70) underlying the southern rim of 30-40-kt 500-mb flow and
60-80-kt 250-mb winds.

Aside from the strength of the flow, little or no other upper
support is evident in terms of sources for large-scale forcing.
Meanwhile, low-level lift will be related to a combination of
boundary-layer troughing over the northeast Gulf and Atlantic, along
with diurnal surface heating and outflow/sea-breeze boundaries
inland. Forecast soundings suggest around 1500-2000 J/kg MLCAPE is
possible, amidst 30-40 kt effective-shear magnitudes, but weak
low-level winds and small hodographs.

…Southwest, southern Plains…
Large-scale lift well east of the ejecting low aloft — mainly in
the form of low-level warm advection — will combine with initially
weak but steadily increasing low-level moisture to support
increasing general thunderstorm potential this evening and
overnight. A few cells late in the overnight over the southern High
Plains may access enough return-flow moisture in the (elevated)
inflow layer to produce hail, but severe potential currently appears
too limited for an outlook.

..Edwards/Gleason.. 11/05/2019


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