WMOD00379

• Title: Potential Opportunities for Precipitation Augmentation in the Eastern Tennessee Valley
• Date: 2/1/1988
• Weather Modification - Doc Type: Report

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2.0 STUDY AREA AND DATA SEr.S

2.1 Study Area

The area of interest for precipitation enhancement activities, as designated by
the TVA, includes parts of eastern Tennessee, western North Carolina and the
extreme southwest corner of Virginia. This area encompasses the highest eleva-
tion watersheds within the TVA region feeding the Tennessee River. Figure 2.1
shows this region, within which four study areas have been prioritized by
desirability for water augmentation. The priorities were provided by TVA. The
highest priority study area was given Priority I and the lowest priority study
area was given Priority IV.

2.2 Precipitation Data

Precipitation data were available from two sources, those being TVA for short
term records and NCDC (National Climatic Data Center) for complete historical
records. The TVA data were available in digital format for 1986 and 1987 in
6-hourly intervals.

The finest temporal resolution data were hourly records available from NCDC.
The NCDC time resolution was desirable, but the information was severely compro-
mised by the quality of the information. Many stations had numerous missing
periods. '

Because of the limited availability of digital TVA precipitation data, and the
uncertain reliability'of NCDC data, it was decided to use the daily precipita-
tion falling in the watershed above Chattanooga (provided by TVA) as an index to
the entire eastern TVA region. This was useful in that a 97-year record exists
of this data so as to allow comparison with the 6 study years used here. It was
believed that this approach would yield much more representative results than
selecting particular stations.

2.3 Upper Air Observations

Upper air observations were available from the National Weather Service rawin-
sonde network. Four rawinsonde stations were found close to the priority study
areas. These stations were located at Athens, Georgia (AHN), Nashville,
Tennessee (BNA), Huntington, West Virginia (HTS), and Greensboro, North Carolina
(GSO). As shown in figure 2.1 the rawinsonde stations surround the study area
with AHN to the south, BNA to the west, HTS to the north, and GSO to the east.
The rawinsonde data were available at 12-hour intervals corresponding to
0700 EST and 1900 EST.

The rawinsonde data provided an opportunity to infer the microphysical charac-
teristics of the clouds. Layers saturated with respect to ice and water were
assumed to be clouds and their temperatures and altitudes were noted.

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