Wednesday, 25 January 2012: 9:45 AM
A Synoptic Overview of the Historic 2010 Mid-South Flood
Room 238 (New Orleans Convention Center )
During 1-2 May 2010, a series of strong thunderstorms distributed prodigious rainfall amounts across the Mid-South region, which contributed to disastrous flooding across portions of central and western Kentucky and Tennessee. Unfortunately, the intense rainfall resulted in 26 fatalities, more than $2 billion dollars in private property damages, and over 11,000 ill-affected structures across the region. Leading up to the event, the synoptic circulation during 29-30 April 2010 was characterized by a broad, developing trough and subtropical ridge pattern over the western and eastern U.S., respectively. Downstream over the Atlantic Ocean, an anomalous closed upper-low circulation and negative NAO (Atlantic ridging) likely enhanced the amplification of the upstream synoptic wave pattern and helped to inhibit the eastward wave progression. Consequently, this upper-air circulation initially forced a steady low-level south-southwesterly surge of considerably warm, moist air across the Tennessee-Kentucky region. According to the HYSPLIT Model, backward air-parcel trajectories near 850 hPa starting from Bowling Green, KY and Camden, TN originated from the Intertropical Convergence Zone (ITCZ) on the Pacific Ocean side of Central America during 29 April. By 1 May, across portions of western and central Tennessee and Kentucky, and into central Indiana, a precipitable water axis with the same orientation as the surface boundary contained values of 37-40 mm, which were +2 standard deviations above normal. By 2 May, precipitable water values within the precipitable water anomaly axis that stretched through Nashville, TN and Bowling Green, KY increased appreciably by nearly 10 mm, to +2 to +4 standard deviations above normal. What makes the 2010 event unique is that the magnitude and quasi-stationary nature of the synoptic pattern was such that a continuous fetch of water vapor from the tropical Pacific ITCZ supplied numerous, long-lasting MCSs with training cells, which resulted in widespread record rainfall totals.