U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 181723 
Storm Prediction Center ac 181722 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1222 PM CDT sun Mar 18 2018 

Valid 191200z - 201200z 

..there is an enhanced risk of severe thunderstorms across parts of 
middle Tennessee...far northeast Mississippi...north-central Alabama 
and northwest Georgia... 

..there is a slight risk of severe thunderstorms from parts of the 
Tennessee Valley into Georgia and northern Florida... 

..there is a marginal risk of severe thunderstorms across parts of 
the middle Mississippi Valley...Ohio Valley...Tennessee Valley and 

Tornadoes, damaging winds and hail are expected across parts of 
middle Tennessee, much of northern Alabama, far northeast 
Mississippi and northwest Georgia. A strong tornado or two is 
possible during the late afternoon. Severe wind gusts are also 
possible into northern Florida. 

..Tennessee Valley/central Gulf Coast states/western and central 
an upper-level low will move across the Ozarks on Monday as a 70 to 
80 kt mid-level jet translates eastward through the base of the 
system. At the surface, a low will gradually deepen as it moves 
eastward into the Tennessee Valley. A warm front extending 
east-southeastward from the low will advance east-northeastward 
across the Tennessee Valley during the day. Scattered elevated 
thunderstorms will likely be ongoing during the morning on the cool 
side of the front in northeast Arkansas and further to the southeast 
in parts of Alabama and Georgia. As the surface low moves into 
middle Tennessee during the mid to late afternoon, surface-based 
convective initiation is expected to occur from near the low 
southward along the Mississippi-Alabama state-line to the west of 
Tuscaloosa. This convection will likely develop southward across 
north-central Alabama and move eastward into western Georgia by 
early evening. Convective coverage should gradually expand and mesoscale convective system 
development will be possible Monday evening. 

Concerning the severe potential, a corridor of moderate instability 
is forecast to develop by afternoon from eastern Mississippi into 
much of Alabama. NAM forecast soundings at 21z in eastern 
Mississippi and near Birmingham show MLCAPE values reaching the 2000 
to 2500 j/kg range. In addition, the mid-level jet will create 
strong deep-layer shear profiles across most of the region. Forecast 
soundings across the slight risk area by late afternoon show 0-6 km 
shear generally in the 60 to 65 kt range. This environment will 
support severe thunderstorm development from the mid afternoon 
through much of the evening. The shear should be favorable for 
supercell formation especially from middle Tennessee southward into 
north-central Alabama where hailstones of greater than 2 inches in 
diameter, wind damage and a tornado threat will be possible. A 
strong tornado may occur with any supercell that can become 
dominant. The potential for very large hail is also forecast 
southeastward into parts of western Georgia where vigorous 
convective development may take place during the early evening. The 
wind damage threat may increase by early evening especially if a 
mesoscale convective system can organize. 

..southern and eastern Georgia/northern Florida... 
An upper-level low will move across the Ozarks on Monday as west to 
southwest mid-level flow remains over much of the southeast. At the 
surface, a low will move into middle Tennessee during the day as a 
warm front advances east-northeastward across Alabama. The 
southeastward portion of the front is forecast to be in place across 
southern Georgia early in the day with this section of the front 
remaining quasi-stationary. Scattered convective development is 
forecast to take place along and south of the front across southern 
and eastern Alabama. This convection should move eastward into 
southern Georgia by early afternoon. 

NAM forecast soundings along and just south of the front at 21z show 
MLCAPE values in the 1000 to 2000 j/kg range with 0-6 km shear near 
50 kts. This environment may support severe thunderstorms with wind 
damage and isolated large hail possible. However, stabilization of 
the airmass could occur as cells increase in coverage due to 
outflow. If storms develop earlier in the day and are a little more 
widespread, the severe threat could be less than anticipated across 
southern Georgia and northern Florida. 

.Broyles.. 03/18/2018