Figure 1. Vertically integrated water vapor transport (IVT) integrated with respect to time from 0000 UTC 1 May to 0000 UTC 3 May 2010, calculated from the 6-hourly 0.5° NCEP Global Forecast System operational analyses. The observed 200-mm (~8-inch) rainfall contour for 0000 UTC 1 May–0000 UTC 3 May is shown in blue. Figure 1.

Figure 2. Schematic illustration of the key atmospheric features and processes for the 1-2 May 2010 Tennessee flood. Figure 2. Click images for more details

Contact:  Benjamin Moore

HMT Publication Notice

NOAA HMT has been exploring a regional implementation of HMT in the Southeastern U.S. following successful efforts in the Western U.S. After the major flood in Tennessee in May 2010 it was decided to explore the physical processes that contributed hydrometeorologically to that disastrous flood. As it turned out, the atmospheric conditions that caused this event included a well-defined atmospheric river (AR). While HMT-West has spearheaded research into ARs in the West, which has led to development and implementation of numerous key tools and data sets, this paper represents the first full documentation of an AR impacting a region in the Eastern U.S. The analysis also led to the development of a diagnostic method whereby the vertically integrated water vapor transport (IVT), which was identified by HMT-West as a key variable identifying AR conditions, is also integrated over time. This highlights the persistence of AR conditions (Fig. 1) that was a key ingredient in the Tennessee flood case documented in this paper. It is important to note that HMT helped sponsor grants through CSTAR focused on QPF, including one led by Dr. Lance Bosart and Dr. Daniel Keyser at SUNY Albany. In addition to that project advancing understanding of the role of "Predecessor Rain Events" (PREs) in extreme rainfall important to the Southeast US, it also helped train a graduate student, Ben Moore, who is the lead on this study. Also, the analysis was contributed to significantly by Faye Barthold, who is located at NCEP/HPC under support from NOAA HMT.

Abstract from Paper:

A multiscale analysis is conducted in order to examine the physical processes that resulted in prolonged heavy rainfall and devastating flash flooding across western and central Tennessee and Kentucky on 1-2 May 2010, during which Nashville, Tennessee, received 344.7 mm of rainfall and incurred 11 flood-related fatalities. On the synoptic scale, heavy rainfall was supported by a persistent corridor of strong water vapor transport rooted in the tropics that was manifested as an atmospheric river (AR). This AR developed as water vapor was extracted from the eastern tropical Pacific and the Caribbean Sea and transported into the central Mississippi Valley by a strong southerly low-level jet (LLJ) positioned between a stationary lee trough along the eastern Mexico coast and a broad, stationary subtropical ridge positioned over the southeastern United States and the subtropical Atlantic. The AR, associated with substantial water vapor content and moderate convective available potential energy, supported the successive development of two quasi-stationary mesoscale convective systems (MCSs) on 1 and 2 May, respectively. These MCSs were both linearly organized and exhibited back-building and echo-training, processes that afforded the repeated movement of convective cells over the same area of western and central Tennessee and Kentucky, resulting in a narrow band of rainfall totals of 200-400 mm. Mesoscale analyses reveal that the MCSs developed on the warm side of a slow-moving cold front and that the interaction between the southerly LLJ and convectively generated outflow boundaries was fundamental for generating convection.