The SPC is forecasting ...Outbreak of tornadoes and severe thunderstorms expected over parts of the southeast US this afternoon and tonight....
the latest public statement about this event. View What is a Watch? clip.
Atlanta, GA...Montgomery, AL...Fayetteville, NC...Sandy Springs, GA...Roswell, GA...
Charlotte, NC...Virginia Beach, VA...Raleigh, NC...Norfolk, VA...Greensboro, NC...
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 221956
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0156 PM CST Sun Jan 22 2017
Valid 222000Z - 231200Z
...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON
AND EVENING ACROSS SOUTHERN GEORGIA...AND NORTHERN FLORIDA INTO THE
WEST CENTRAL FLORIDA PENINSULA...
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
HIGH RISK AREA...INCLUDING MUCH OF THE REMAINDER OF CENTRAL
FLORIDA...THE REMAINDER OF CENTRAL AND SOUTHEAST GEORGIA AND MUCH OF
THE SOUTH CAROLINA PIEDMONT AND COASTAL PLAIN...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
MODERATE RISK AREA...INCLUDING PORTIONS OF SOUTHERN NORTH
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK AREA...INCLUDING PARTS OF NORTHEAST ALABAMA...NORTHERN
GEORGIA...UPSTATE SOUTH CAROLINA AND MUCH OF THE REMAINDER OF
SOUTHEASTERN NORTH CAROLINA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...THROUGH THE NORTH CAROLINA PIEDMONT AND PORTIONS
OF SOUTHEAST VIRGINIA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING ACROSS PARTS OF THE CENTRAL CALIFORNIA
COAST...INCLUDING THE SAN FRANCISCO BAY REGION...
An outbreak of severe thunderstorms, including the risk for strong
tornadoes, and very strong damaging wind gusts, appears likely late
this afternoon through tonight across southern Georgia into the
Carolinas, and much of Florida.
...20Z Outlook Update...
In response to large-scale forcing for ascent, vigorous thunderstorm
development is now underway within a narrow pre-cold frontal
corridor, from portions of eastern Alabama southward into the
northeastern Gulf of Mexico. Severe categorical and probabilistic
lines remain generally unchanged outside of Florida, except to begin
to account for the eastward progress of the front/evolving
There remains some lingering uncertainty concerning the extent of
boundary layer destabilization across parts of northern Georgia
through the Carolinas, along/north of a northward retreating outflow
boundary/warm front. Otherwise, the primary lingering uncertainty
concerns the extent to which convective cells remain discrete within
the pre-frontal convective band.
The continued upscale growth of convection into a solidifying squall
line seems most probable in association with an area of stronger
mid/upper forcing for ascent likely to overspread much of northeast
Florida and southeastern Georgia into South Carolina through this
evening. If/when this occurs, severe wind potential is likely to
increase considerably in the presence very strong low-level and deep
layer wind fields. Latest model guidance continues to suggest an
intense southerly 850 mb jet streak (50-70+ kt) developing/shifting
northeastward from the northeastern Gulf of Mexico through this
region. And heavy precipitation loading coupled with downward
momentum transfer seems likely to support considerable damaging wind
potential, including at least localized intense surface gusts in
excess of 65 kt.
Otherwise, strong to extreme low-level shear, with very large,
clockwise-curved low-level hodographs will support the potential for
long-lived/long track supercells, in the presence of weak to modest
warm sector boundary layer instability. This activity may impact
the Tampa/St. Petersburg metropolitan area by early evening, and
much of the remainder of the central and southern Florida Peninsula
through tonight. Severe probabilities have been increased in
general across this region to account for this.
...Central California, including the San Francisco Bay area...
No changes have been made, with models suggesting a 110-130 kt
westerly 500 mb jet streak nosing inland across the coast late this
afternoon and evening. Destabilization mostly within the post-cold
frontal environment may become sufficient to support inland
advancing low-topped convection/convective bands accompanied by a
risk for potentially damaging surface gusts.
.PREV DISCUSSION... /ISSUED 1028 AM CST Sun Jan 22 2017/
...AN OUTBREAK OF SEVERE STORMS AND TORNADOES IS EXPECTED THIS
AFTERNOON AND EVENING OVER PARTS OF NORTHERN FLORIDA, AND
...Southern AL/North FL/Southern GA...
The late morning surface analysis shows a rapidly deepening low near
MOB, with a convectively reinforced warm front extending eastward
from the low along the FL/GA border. This low is forecast to deepen
over 12mb in the next 12 hours as it tracks northeastward. This
rapid cyclogenesis will be accompanied by very strong low and mid
level wind accelerations across parts of GA/FL. The result will be
a zone of impressive shear profiles in the warm-sector of the low,
along with ample low level moisture and rather steep lapse rates.
Forecast soundings in the HIGH risk area are characterized by
effective helicity values of 500-700 m2/s2 overlapping MLCAPE of
1000-1500 J/kg. This rare parameter space will support the risk of
long-track strong tornadoes across the HIGH risk area. Also, very
strong low and mid level winds and steep lapse rates suggest a
significant risk of bowing structures capable of widespread damaging
winds and large hail. The line of storms will eventually sag
southward across the entire FL Peninsula overnight with a continued
...Northeast AL/Northern GA...
As the rapidly deepening surface low lifts northeastward, a plume of
rather steep mid level lapse rates and strong winds aloft will wrap
around the low. This may result in an arc of strong to severe
storms affecting parts of northeast AL and northern GA later this
afternoon and evening. Ample low level vorticity along this arc may
be sufficient for a few tornadoes, along with large hail and
damaging wind gusts.
The convective evolution is uncertain over parts of SC/NC later
today due to the widespread upstream thunderstorm coverage expected,
and the persistent thunderstorm complex now over southeast GA.
Given the strength of the wind fields and cyclogenesis, there
remains a significant threat of severe storms spreading
northeastward across much of SC and into southeast NC after dark,
with damaging winds and a few tornadoes being the main threat. Its
unclear how far north and west this threat will extend, but have
lessened severe probabilities over parts of western/central NC where
cool air and clouds are likely to persist.
...Central CA Coast...
Multiple bands of showers and thunderstorms are expected to spread
inland and affect the central CA coast this afternoon. Cool
temperatures aloft and steep mid level lapse rates, combined with
the strong west-southwesterly winds aloft, will support a risk of
fast-moving bowing structures capable of locally damaging winds and
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