QLCSQuasi-Linear Convective System
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It is noteworthy that five EF-2 to EF-3 tornadoes within the morning QLCS produced damage path widths exceeding 1 km.
Early morning QLCS. A large MCS formed over the LA-AR region and organized over MS around midnight CDT (0500 UTC) on 27 April.
Component 1 rapidly expanded to form a bow echo after 0735 UTC, while the others merged into one contiguous QLCS that produced 31 tornadoes in central to northern AL.
A second significant MV (MV2) formed within this QLCS by 1030 UTC.
Based on initial results, we note the following apparent aspects of MV2: 1) it contained multiple vorticity centers at some analysis times; 2) cores of vertical vorticity from the northernmost convective cells along the attendant QLCS to the south advanced toward MV2 and merged with the primary vorticity area; 3) updrafts were shallow and relatively weak (<10 m [s.sup.-1]) and their magnitudes peaked below 6-km height on the northern to western sides of the vortex; and 4) the storm-relative horizontal wind maximum migrated counterclockwise with time.
Other special observations include a sounding just ahead of the QLCS at 1700 UTC from Redstone Arsenal, AL (RSA), measurements from the MAX radar 42 km northeast of the ARMOR, and the passage of the southern portion of the QLCS over the MIPS.
5d) that produced wind damage across northern AL and eventually overtook and merged with the leading QLCS by 1800 UTC.
It is noteworthy that the early morning and midday QLCS events produced significant local power outages from central to northern AL that significantly reduced warning dissemination (owing to power outages, disabled sirens, and reduced weather radio transmissions) to these areas during the more significant afternoon supercell-spawned tornadoes (TRAC 2012).
The thermal boundary produced by the midday QLCS and reinforced by subsequent overcast and scattered showers within the northern portion of the outbreak area was a prominent mesoscale feature.
9), where surface temperatures of ~17[degrees]C were maintained after the midday QLCS by persistent rain showers and cloud cover.
On 27 April an early morning cluster of meso-[beta]-scale components coalesced over MS to form a long QLCS, within which two mesoscale vortices (MV1 and MV2) formed.
Following a midday QLCS that produced seven EF-0 to EF-1 tornadoes over northern AL, supercell storms developed during the afternoon hours in an extremely favorable environment, producing the majority of EF-3 to EF-5 tornadoes and associated large numbers of fatalities (316), injuries (> 2700), and damage (~$11 billion).