The SPC is forecasting ...Severe thunderstorms expected over parts of the Tennessee Valley this afternoon and tonight....
the latest public statement about this event. View What is a Watch? clip.
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 192000
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Mon Mar 19 2018
Valid 192000Z - 201200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF FAR NORTHEAST MISSISSIPPI...MIDDLE TENNESSEE...NORTHERN
ALABAMA...AND NORTHWEST GEORGIA...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
MODERATE RISK AREA...AND EXTENDING EAST INTO PARTS OF CENTRAL
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
MODERATE AND ENHANCED RISK AREAS...AND INCLUDING A LARGER PORTION OF
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
OTHER/ASSOCIATED RISK AREAS...
Strong tornadoes, very large hail, and damaging winds are expected
across parts of the Tennessee Valley and Southeast during the late
afternoon and evening.
The existing outlook areas, and associated forecast reasoning,
remain valid and in line with current thinking. The main
adjustments to the outlook at this time will be confined to minor
tweaks, mainly to remove areas near the mid-Mississippi Valley where
the front has progressed eastward, and some tweaks to the tornado
risk over middle Tennessee where it has been slow to destabilize.
Otherwise, convection continues to increase as breaks in the clouds
from Tennessee south to northeast Mississippi and northwest Alabama
are allowing gradual northward destabilization to occur. With the
strongest ascent now spreading into the Tennessee Valley per the
latest WV imagery, and as the deep-layer wind field across the area
correspondingly strengthens with time over the next few hours,
expect several severe/supercell storms to evolve along with
attendant severe/tornado potential.
.PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Mar 19 2018/
...TN Valley and Southeast...
Have upgraded to Moderate risk for the increasing likelihood of
several tornadic supercells between 21-03Z, centered on northern AL
and portions of adjacent states. Expansions to Enhanced and Slight
risks have also occurred across parts of GA and SC for this evening
and tonight. Lowest confidence remains on northern extent of the
strong tornado risk where the degree of surface-based
destabilization is quite uncertain.
An elevated storm cluster is ongoing across far northern MS to the
Mid-MS Valley, still removed from appreciable surface-based
instability that is present near/south of the warm front in
north-central MS/AL. See MCD 144 for additional short-term
information. Guidance is highly varied in the degree of warm front
movement today, which may be in part explained by differences in the
handling of the ongoing convection. The NAM robustly destabilizes
into middle TN but has a distinct absence of convective precip where
convection is ongoing. While the RAP has substantially less buoyancy
in TN with SBCAPE >500 J/kg remaining largely south of the state
border. While low/deep-layer shear and hodograph size will become
increasingly favorable for rotating storms, confidence in the degree
of northward destabilization in the late afternoon across TN is low.
However, farther south in parts of MS/AL/GA, confidence is greater
in moderately large buoyancy developing with MLCAPE of 1500-2500
J/kg becoming common south of the warm front. The northern extent of
this instability plume with enlarged low-level hodographs should
render the potential of several tornadic supercells during the late
afternoon and early evening, a couple of which may be long track.
Morning CAMs suggest the southern extent of probable supercell
development will be across north-central AL, with convection
becoming increasingly sparse to the south/southwest.
During the evening, convection should become increasingly
clustered/semi-discrete, but a risk for a few strong tornadoes
should continue across parts of northern/central GA near the warm
front. Damaging wind/tornado risk should persist but become
increasingly localized across parts of SC tonight.
A separate area of scattered storm clusters should emanate northeast
from ongoing convection along the FL Gulf Coast. This activity
should be aided by a minor mid-level impulse evident over LA and
modest warm advection atop a modifying outflow boundary in the wake
of an early morning MCS that traversed north FL. A few embedded
supercells capable of all hazards are possible with this activity.
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