SPC AC 220600
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1200 AM CST Sun Jan 22 2017
Valid 221200Z - 231200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF SOUTH CENTRAL THROUGH SOUTH GEORGIA INTO NORTHERN FLORIDA...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF THE SOUTHEAST STATES...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A LARGE PART
OF THE SOUTHEAST STATES...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A LARGE
PART OF THE SOUTHEAST STATES...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE SAN
FRANCISCO BAY AREA...
Severe thunderstorms accompanied by a risk for damaging winds, large
hail and tornadoes (a few of which could be strong) are expected
across parts of the Southeast today into this evening. A more
marginal threat for a few severe storms with damaging wind gusts is
expected around the San Francisco Bay area into nearby portions of
the Sacramento and San Joaquin Valleys.
Thunderstorms will likely be ongoing generally along and north of
warm front from northern AL through northern and central GA and SC.
Initial low-level jet associated with lead impulse will continue
through the eastern Carolinas and offshore early in the day. Early
storms along the warm front should continue advancing north. By mid
day this front should extend from a surface low in south central AL
through south-central and southeast GA and will move farther north
during the afternoon. Rich boundary-layer moisture resides along the
Gulf Coast region with dewpoints in the upper 60s to around 70F. An
intense 60+ kt secondary low-level jet is forecast to develop by
late morning into afternoon from northern FL into southern GA within
exit region of a progressive upper jet. The coupled jet structure
will contribute to very large low-level hodographs and strong deep
shear in vicinity of warm front as well as in warm sector.
Initial severe threat will probably evolve along and just ahead of
the cold front across southern Alabama into the FL Panhandle as
forcing for ascent within the upper jet exit region interacts with
warm sector. Supercells and bowing segments with large hail and
damaging wind will be the initial primary threats, but a few
tornadoes will also be possible. The environment will become
increasingly supportive of supercells with low-level mesocyclones
and tornadoes as the secondary low-level jet strengthens and the
boundary layer destabilizes from southeast AL into south central and
southern GA as well as northern FL. Additional storms will likely
develop along the eastward-advancing cold front including potential
for supercells with bowing segments capable of large hail, a few
tornadoes and damaging wind.
Potential complicating factor with northward extent into the
Carolinas and GA is impact of ongoing convection on destabilization
potential, but will maintain at least an enhanced due the expected
northward progression of the warm front. Additional storms will
likely develop along the cold front farther south across the FL
Peninsula during the afternoon and evening where vertical wind
profiles will support organized severe storms.
...San Francisco Bay area...
Exit region of an intense (110-130 kt) westerly 500 mb jet streak
will spread southward across the region later today. Cooling aloft
should contribute to at least weak destabilization in the moist
post-frontal onshore flow regime. Strong deep shear will be in
place, and model guidance suggests a forced low-topped convective
band could spread inland across the San Francisco Bay area,
accompanied by the risk for strong wind gusts. Other, more
discrete, convective cells could form ahead of this band, across
nearby portions of the interior valleys, perhaps with some risk for
a brief/weak tornado.
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