|Synoptic Analysis of The "Super Tuesday Outbreak"|
of the Southern United States
and It's Impacts on the Region
Typically "Super Tuesday" is synonymous with presidential primaries, political speeches, and news media
clambering to cover the hectic events of the night, but the election took a back seat for people living
in the southern U.S. on February 5, 2008. One of the largest and most deadly tornado outbreaks in more
than 20 years took place as the ballots were starting to pour in for the night. Some locations in
Tennessee and Arkansas that were participating in the primary elections were even forced to close
the polls early as a result of the severe weather that would affect the area.
At 10:16 A.M. CST, February 5, 2008 the Storm Prediction Center (SPC), a division of the National Oceanic
and Atmospheric Administration (NOAA), in Norman, OK issued their Day 1 convective outlook for the day. What
can be somewhat of a mundane task most often in the winter months was no typical late winter forecast at
all. This would be a very active weather day across the entire eastern half of the United States and
particularly the southern region of the country as well as the National Weather Service agencies
across the areas that were impacted. There was a high risk for severe weather in the mid-south
with the primary area affected being an area encircling Arkansas and extending into Western
Tennessee and Northern Louisiana which is shown below. Also illustrated is a moderate to
slight probability sector surrounding this area which included the majority of the eastern
United States. The SPC concluded that the atmospheric variables were favorable for severe
thunderstorms, large hail, damaging winds, and long-lived supercell development. Significant
tornadoes associated with these supercells were the largest concern of the day and a high
probability of their occurrence was also acknowledged and addressed in detail in the
mesoscale discussion contained on the SPC website for the day. The prediction of the
SPC panned out which was an unfortunate turn of events for many people in
the southern United States.
There were many different atmospheric factors that contributed to the synoptic-scale weather pattern that
were consistent for major outbreaks of tornadoes and severe weather. The event was a conglomeration of
different parameters with the main one being a powerful low pressure that was closing in from the Great
Plains states. Another pivotal factor was that the south experienced many record-breaking temperatures
during the day with some areas reaching 80°F! The high temperatures were associated with strong
southerly winds and the warm air advection (WAA) that resulted from these winds. Temperatures
typically ranged from mid 60's to 70's with the boundary layer being very moist having dew
points reaching into the high 50's to mid 60's throughout the majority of the region. The strong
WAA into the region enhanced the moisture and heat that had already obtained record-breaking levels.
Even after sunset in most regions, the temperature dropped minimally leaving high dewpoints in
a nearly saturated environment which supplied copious amounts of moisture to the
thunderstorms. Further destabilization of the atmosphere was able to take place due to the
high temperatures in the planetary boundary layer (PBL) which acted as a lifting mechanism
to the severe storms. Secondly, a deep upper level trough extended from the southern plains
into the gulf coast states and back through the Ohio River Valley in association with a strong
area of low pressure centered over the Kansas City, MO area. Due to the counterclockwise
circulation of the low, a strong cold front was slowly migrating southeast along a path
from the Ohio River Valley to eastern Texas which was an area that was conversely experiencing
low-level WAA into the region. This was the primary source of lift that was necessary in
order to produce the severe weather that was experienced in the area. These conditions
were accompanied by strong winds in the mid and upper levels ranging from 90 knot at
500 mb level to 130 knots at the 250 mb layer. This increase with height caused
significant speed shear. In the Ohio valley, which was experiencing some of the
strongest upper level winds, the result was that of a long lived squall line in
which a widespread derecho event occurred. Positive vorticity advection (PVA)
was also occurring in an area from Texas into Tennessee following the upper level
flow. An area of difluence, an area where winds on the same plane are flowing at
angles away from each other, developed over western Tennessee and assisted in the
development of supercells in this region. Difluence aids uplift by pulling up air
from below to fill the void left in the area due to the spreading apart motion of
the wind. In addition to all of this, there was also a weak cap that existed in the
region which was quickly broken through as the convection increased through the daytime
hours resulting in an explosion of severe weather. The convective storms exploded
throughout the day and the unstable environment along with upper level winds and
moisture source helped to maintain this extremely powerful system. Below is a
500 millibar (mb) weather chart from 12Z on February 6 which shows the vorticity
maximum and flow around the deep low pressure and trough that were important factors
in the outbreak.
Tornadoes in February are not necessarily rare, but statistically speaking they only make up 5% of the
annual tornado distribution in the United States. The unseasonably warm temperatures were primarily due
to La Nina event of this past winter. The system was similar to an early spring type setup with the
extreme warmth of the predominant temperatures that were present in the region. The combination of
warm temperatures and the strong cold air mass that was advecting into the area combined to produce
a perfect environment for a large scale severe weather event.
After all was said and done, there were a total of 131 tornadoes reported. The death toll totaled 57 with
several hundred more being injured. The areas hardest hit were those of Arkansas, Alabama, Kentucky, Tennessee,
and Mississippi. The majority of the tornadoes reported were from several long lived supercells that traveled
through these states. Tennessee was the hardest hit with a total of 32 fatalities in the deadliest outbreak
in 34 years for the state. Arkansas was also in the path of system and was the first area of the mid-south
to experience the fury of the storms that afternoon and night. Arkansas had a single tornado that trekked
a total of 123 miles, which is longest path of a single tornado ever recorded in the state since
detailed records began to be kept there in 1950. Deaths in the state totaled 13 from the storms. The
majority of the Midwest was spared from the tornadic storms, but the intense squall line that caused
some straight line wind damage from southeastern Illinois all the way over to western West Virginia
was nonetheless a very widespread and significant event. To the northwest of the system there was
a major winter storm that was triggered in the cold sector of the low pressure system. Property
damage is still being reported for the outbreak. Below is a map of the tracks of the supercells
and their associated tornadoes and the location of the squall line that progressed through the
region. "Super Tuesday" will forever have an alternate meaning for those of us who forecast
and monitor weather. This was a very memorable and significant event in the meteorological
community that will not be soon forgotten.
Feb, 2008 1630 UTC Day 1 Convective Outlook. Storm Prediction Center.
Retrieved Mar. 22, 2008.
Preliminary Tracks/County-Fatalities and State-Fatalities For Feb. 5-6,
2008 Outbreak. Greg Carbin, Greg and Thompson, Daphne. Storm Prediction Center.
Retrieved on Mar. 23, 2008.
Severe Storms. National Climatic Data Center. Retrieved on Mar. 23, 2008.
"Super Tuesday" Outbreak Weather Summary. National Weather Service Forecast Office in Huntsville, AL.
Retrieved on Mar. 23, 2008.
U.S. Tornado Climatology. National Climatic Data Center. Retrieved on Mar. 22, 2008.