The Top 11 of '11: Mid-South weather stories from MWN (part 3)

Continuing on in typical year-end countdown fashion, today's post contains weather events #5-6 in our "Top 11 of '11" - Mid-South weather stories of 2011. If you missed numbers 7-11, you can find them in part 1 and part 2 of this blog series.  Before I forget, let me also thank MWN intern Kevin for being a major contributor to this series!  If you follow MWN on Twitter (and if not, you should be), you'll recognize the next two stories as #memstorm events.

# 6. Early April severe weather events foreshadow a busy season
With the spring severe weather season upon the Mid-South, by early April few notable events had taken place. The most significant event to that point was a strong squall line of thunderstorms which passed through the northern portions on February 24. However, April wouldn't be around long before the severe weather season kicked into high gear with two high-impact events affecting the metro in a two-week period.

The first significant severe weather outbreak took shape on April 4. With a powerful upper level disturbance moving out of the Southern Plains, combining forces with a strong surface cold front and low pressure area, numerous thunderstorms began developing over Arkansas on the morning of the 4^th, quickly moving east. By noon, the thunderstorms began congealing into a large line segment as they crossed the Mississippi River, tapping into abundant low-level moisture and instability in place. This led to rapid intensification of the storms as they moved through the metro area, resulting in widespread, damaging straight-line winds. Wind gusts of 60-80+ mph led to numerous downed trees, power lines, and even some structural damage. Power outages were widespread with 70,000+ customers in the MLGW service area losing power. The line of thunderstorms continued growing and organizing as it pushed east, resulting in a nearly continuous swath of severe weather across the Southeast over the next 24 hours. In fact, the linear storm system, known as a “derecho” (like “Hurricane Elvis” in 2003), resulted in one of the largest severe thunderstorm outbreaks on record, with over 1400 reports of severe weather received (see image to left).

In the days following the April 4 outbreak, several smaller severe weather events affected the metro, including a damaging wind event on April 15, but it was April 19 when the next notable outbreak began to evolve. Very similar to the events of April 4, thunderstorms began forming over Arkansas and, as they approached the metro area during the evening, they began consolidating into a squall line, producing damaging straight-line winds. As the storms pushed east, the most significant damage again occurred in Shelby County. Wind gusts of 60-75 mph led to more downed trees, power lines and minor structural damage. This meant more significant power outages with 64,000 MLGW customers affected, some being the same who lost service on April 4. While the event wasn’t as intense as April 4, the rapid succession of severe weather during the month was already beginning to take its toll on Mid-South residents.

With April starting off on such an active note, some began to wonder if these events were just a foreshadowing of things to come and whether the worst was yet to come. Unfortunately and tragically, the 2011 severe weather season was just unfolding.

# 6. Severe weather season ends with one last round of storms in late May

Severe weather season was particularly harsh in 2011, starting with the early April rounds described above and continuing all the way until the end of May.  For the Mid-South, after 6 weeks of strong weather systems, nerves were frayed leading up to the last week in May as local meteorologists (MWN included) began building up an event that would take place on Wednesday, May 25, with the passage of another strong cold front.  The "edgy-ness" only got worse after the same storm system dropped an EF-5 bomb on Joplin, MO on May 22.

On the morning of the 25th, the Storm Prediction Center placed west TN and east AR under a "High Risk" threat (see image) - something we only see a couple of times a year at most - and indicated the "threat for tornadoes, some potential strong to violent and long-tracked" as they issued a Tornado Watch for the metro at 12:30pm.  A broken line of supercells formed along the cold front to our west in the afternoon and swept across the river into a moist and very unstable airmass during the early evening. Several Tornado Warnings were issued during the evening and there were several reports of large hail and damaging wind, though thankfully no tornadoes were ever confirmed.  The event could have been much worse given the conditions that had set up ahead of the system and it's history over previous days.  This round of severe weather would mark the end of severe weather season for the Mid-South and the start of one of the hottest summers on record.  More on that as we continue to countdown the biggest Mid-South weather events of 2011 (tease...)  Tomorrow we bring you events #4 and 3, with the top 2 weather stories of 2011 coming on New Year's Eve.

A reminder that during severe weather, MemphisWeather.net uses social media (specifically Facebook and Twitter) to "nowcast" events as they unfold.  We'll tell you where the storms are, where they are going, who they will affect and how, and when things have calmed down, all in our no-nonsense, no-hype manner. Join us, won't you? 8,000 others can't be wrong!