April 27 - 29th Tornado Outbreak
The 2014 severe weather season started out very slowly, which was welcomed by many residents across the United States. In fact, tornado reports were on track with some of the lowest levels in recorded history (see graphic). Unfortunately, that would all change during the last week of April, with a major tornado outbreak striking the southern Plains and Deep South from April 27 - 29th. This outbreak produced 164 tornado reports over the 3 day span, with 69 confirmed tornadoes (so far) and sadly 35 U.S. residents lost their lives. Let's delve deeper into the cause of the outbreak.
Above is a depiction of the set-up on April 28th, which was by far the most active day of the outbreak, with 115 tornado reports. As you can see, there was an expansive area of low pressure centered over the heartland of the country. This system was sucking in low-level moist air from the Gulf, creating an unstable environment over the Gulf States. Meanwhile, strong upper level winds were tearing across the Rockies, into MS, AL and TN. This type of set-up creates turning in the atmosphere with height, which is conducive for rotating storms or supercells. Add in a cold front pressing in from the west as the trigger, and these supercells exploded over the south.
This atmospheric pattern produced many tornadoes, some of which were long-track and violent tornadoes. Several EF-3 and a few EF-4 tornadoes were reported with track lengths of 20 to 40 miles and widths of 1/4 to 3/4 mile (EF scale). Two of the strongest tornadoes occured in Vilonia, AR on the 27th and Louisville, MS on the 28th. These tornadoes were rated EF-4 with winds of 180 - 190 mph. While both tornadoes were 3/4 mile wide, the Vilonia twister was on the ground for almost 1 hour and traveled a length of 41.3 miles north of Little Rock, AR. This tornado destroyed almost everything in its path, as seen the aerial image below from NWS Little Rock:
Even the bigger cities could not escape the tornado outbreak, with Jackson, MS brushed by to the south and Tupelo, MS taking a direct hit. These tornadoes were both rated EF-3, cutting paths around 30 miles long and up to 1/4 mile wide. Winds were estimated to be between 150 and 155 mph. Below, you can see the tornado vortex signature (TVS) south of Jackson, MS from the National Weather Service radar (which had a very close shave with the same tornado):
After this major outbreak, hopefully we will see another calm period with respect to tornadoes and severe weather.