Severe Weather to strike the Southeast

An outbreak of severe thunderstorms is likely Wednesday across much of the Southeast, continuing northward along and west of the Appalachians into the Tennessee and Ohio Valleys.  This will include supercell development with a risk for tornadoes, some of which will be strong and long-lived, particularly across the Southeast. Large to very large hail and damaging straight-line winds also appear likely.

severe

MODERATE 103,173 14,567,637 Atlanta, GA…Birmingham, AL…Montgomery, AL…Columbus, GA…Huntsville, AL…
ENHANCED 122,034 17,242,602 Indianapolis, IN…Nashville, TN…Cincinnati, OH…Lexington-Fayette, KY…Louisville, KY…
SLIGHT 149,867 22,769,267 Jacksonville, FL…Columbus, OH…Charlotte, NC…Virginia Beach, VA…Raleigh, NC…
MARGINAL 118,145 18,253,000 Tampa, FL…St. Louis, MO…St. Petersburg, FL…Fort Wayne, IN…Orlando, FL…

Thunderstorms are spreading across portions of the Florida panhandle, Southeast Alabama and Southwest Georgia early this morning.  These storms will spread northeast and continue to grow throughout the day.   Hail looks to be the early risk here.

SIG SEVERE 84,950 13,240,373 Atlanta, GA…Birmingham, AL…Montgomery, AL…Columbus, GA…Huntsville, AL…
45 % 85,208 13,300,208 Atlanta, GA…Birmingham, AL…Montgomery, AL…Columbus, GA…Huntsville, AL…
30 % 139,977 18,619,298 Indianapolis, IN…Nashville, TN…Cincinnati, OH…Lexington-Fayette, KY…Louisville, KY…
15 % 150,323 22,775,864 Jacksonville, FL…Columbus, OH…Charlotte, NC…Virginia Beach, VA…Raleigh, NC…
5 % 118,900 18,265,296 Tampa, FL…St. Louis, MO…St. Petersburg, FL…Fort Wayne, IN…Orlando, FL…

This situation looks to be very dangerous, and while a high risk has not yet been issued, it is still possible for one to be issued later in the day.   Many schools have already closed due to the threat and Alabama has pre-emptively declared a state of emergency.  Please take whatever time you have available to make preparations this morning.  This is the current risk for tornadoes.

SIG SEVERE 68,331 7,831,596 Columbus, GA…Huntsville, AL…Chattanooga, TN…Columbia, SC…Macon, GA…
15 % 82,670 12,969,607 Atlanta, GA…Birmingham, AL…Columbus, GA…Huntsville, AL…Chattanooga, TN…
10 % 96,170 14,611,391 Indianapolis, IN…Nashville, TN…Cincinnati, OH…Lexington-Fayette, KY…Louisville, KY…
5 % 145,835 20,161,059 Charlotte, NC…Raleigh, NC…Norfolk, VA…Greensboro, NC…Chesapeake, VA…
2 % 58,628 7,655,933 Columbus, OH…Virginia Beach, VA…Richmond, VA…Newport News, VA…Hampton, VA…

Model Analysis

A highly amplified trough will be present across the Plains at the beginning of Wednesday morning.  This trough will move eastward to the Mississippi Valley by Wednesday evening and continue to the Ohio and Tennessee River Valleys and Southeast by early Thursday morning. Strong mid-level southwesterly winds will overspread much of the Ohio and Tennessee Valleys and Southeast during peak daytime heating.  These winds will then overspread much of the East Coast Wednesday evening through Wednesday night.

Gulf moisture will move northward across portions of Mississippi, Alabama and Georgia this morning.  This moisture will shift eastward across Georgia into the Carolinas and Virginia through the afternoon and early evening before strengthening further late Wednesday into early Thursday morning across the Mid-Atlantic.

The corridor of strong south to southwesterly low-level winds will also overspread much of the Ohio and Tennessee Valleys through by Wednesday night as a warm front advances northward. An area of low pressure initially over southeastern Missouri will develop northeastward into Illinois and Indiana by Wednesday evening.  This strengthening low will then slowly continue northeastward to the vicinity of the eastern Great Lakes by Thursday morning.

A cold front associated with this low will move eastward across the Ohio and Tennessee Valleys and Southeast Wednesday, reaching the Mid-Atlantic by Thursday.

Severe Thunderstorm Watch

A Severe Thunderstorm Watch has already been issued this morning and additional watches are expected as the day goes on.  Large hail is the primary risk with these storms but a tornado cannot be ruled out.

Southeast into the Mid-Atlantic

A very moist warm sector with low 70s F dewpoints will reside south of northward-advancing warm front across the Gulf Coast states.  Warm air advection should cause convection to form along the warm front early Wednesday morning across parts of eastern Mississippi, Alabama, and Georgia. This initial activity will pose a threat for all severe hazards, including tornadoes along and south of the front where surface-based convection will be more likely.  Additional supercell development appears likely within the broad warm sector across the central Gulf Coast States, particularly across Alabama into Georgia and South Carolina Wednesday morning and afternoon as large-scale ascent associated with the upper trough begins to overspread the region.

Forecast soundings across this region suggest strong tornadoes will be possible with any discrete storm that can form in this environment, in addition to very large hail and damaging straight-line winds.  Severe probabilities have been increased and expanded slightly into western Alabama and eastern Mississippi with latest model guidance showing convective development both Wednesday morning along the warm front and again Wednesday afternoon along the cold front.

As the convection that develops Wednesday morning and early afternoon moves across the Carolinas in the evening, instability will increase and result in strong to severe storms across parts of the Carolinas into southeastern Virginia.  If convection can become surface based in this region, then all severe hazards may occur, including a threat for tornadoes.  Severe probabilities across the Carolinas and southern Virginia have been increased to account for this threat late Wednesday night.  Organized Thunderstorm development is expected across the Mid-Atlantic on Thursday as this brings gulf moisture up ahead of the cold front.

 

   Ohio and Tennessee River Valleys

The northward advance of low-level moisture will be more limited across the Ohio and Tennessee Valleys Wednesday, but will still be more than sufficient with dewpoints near 60F ahead of the approaching cold front.  A band of supercells appear likely per latest model guidance.  These storms should be capable of producing tornadoes, very large hail and strong damaging winds.  Eventual growth into mixed modes with line segments may occur during the evening as activity approaches the Appalachians.