Archive:2011 Eclectic–Lake Martin tornado

Template:Short description Template:Use American English Template:Use mdy dates Template:Infobox weather eventTemplate:Infobox weather event/TornadoTemplate:Infobox weather event/EffectsTemplate:Infobox weather event/Footer On the afternoon of April 27, 2011, A large and deadly tornado went through the southern parts of Alabama, Part of a very large and deadly tornado outbreak, witch is the largest and costliest Tornado Outbreak in United States history.

Meteorological synopsis

2011 Super Outbreak#Meteorological synopsis

Setup

The environmental conditions leading up to the 2011 Super Outbreak were among the "most conducive to violent tornadoes ever documented". On April 25, a vigorous upper-level shortwave trough moved into the Southern Plains states. Ample instability, low-level moisture, and wind shear all fueled a significant tornado outbreak from Texas to Tennessee; at least 64 tornadoes touched down on this day. An area of low pressure consolidated over Texas on April 26 and traveled east while the aforementioned shortwave trough traversed the Mississippi and Ohio River valleys. Another 50 tornadoes touched down on this day. The multi-day outbreak culminated on April 27 with the most violent day of tornadic activity since the 1974 Super Outbreak. Multiple episodes of tornadic activity ensued with two waves of mesoscale convective systems in the morning hours followed by a widespread outbreak of supercells from Mississippi to North Carolina during the afternoon into the evening.

Tornadic activity on April 27 was precipitated by a 995 mbar (hPa; 29.39 inHg) surface low situated over Kentucky and a deep, negatively tilted (aligned northwest to southeast) trough over Arkansas and Louisiana. A strong southwesterly surface jet intersected these systems at a 60° angle, an ageostrophic flow that led to storm-relative helicity values in excess of 500 m²s⁻²—indicative of extreme wind shear and a very high potential for rotating updrafts within supercells. Ample moisture from the Gulf of Mexico was brought north across the Deep South, leading to daytime high temperatures of Template:Convert/to and dewpoints of Template:Convert/to. Furthermore, convective available potential energy (CAPE) values reached 2,500–3,000 J/kg⁻¹.

Forecast

Template:Multiple image On the morning of April 27, a strong cold front with several areas of embedded low pressure extended from the Texas Hill Country northeastward towards the Arklatex and the Ozarks, and later into the lower Ohio Valley. Warm moist air was in place due to strong southerly flow ahead of the front over Mississippi, Alabama, and Tennessee. An upper level disturbance sparked a broad area of showers and thunderstorms as it moved across the frontal boundary on the previous evening. The eastern edge of the line of showers and storms continued to move eastward, in concert with the upper disturbance, reaching the northwest Alabama border around 2:00 a.m. CDT.

This produced the last and most violent round of severe weather, which began around 2:30 p.m. CDT for northern Alabama as supercells began to line up to the southwest of the area. During the early afternoon hours, the potential for destructive tornadoes was highlighted by the Storm Prediction Center's upgrade to a high risk for severe weather around 1:00 p.m. CDT. This prompted a particularly dangerous situation (PDS) tornado watch, which was issued for northern Alabama and portions of southern Tennessee at 1:45 p.m. CDT. The bulletin that accompanied the watch read: Template:Blockquote The potential for tornadoes ramped up from noon through 9:00 p.m. CDT. During this period, much of Alabama experienced numerous supercell thunderstorms that produced numerous tornadoes, including the Lake Martin tornado.