Upper air codes for all of the sounding sites in the PDF file:

ABR - Aberdeen, South Dakota
AMA - Amarillo, Texas
BIS - Bismarck, North Dakota
BUF - Buffalo, New York
CHS - Charleston, South Carolina
CRP - Corpus Christi, Texas
DDC - Dodge City, Kansas
DNR - Denver, Colorado
DVN - Davenport, Iowa
FWD - Dallas/Ft. Worth, Texas
GGW - Glasgow, Montana
GRB - Green Bay, Wisconsin
GSO - Greensboro, North Carolina
IAD - Sterling, Virginia
ILN - Wilmington, Ohio
INL - International Falls, Minnesota
JAN - Jackson, Mississippi
LBF - North Platte, Nebraska
LZK - Little Rock, Arkansas
MAF - Midland, Texas
MPX - Minneapolis, Minnesota
OAX - Omaha, Nebraska
OUN - Oklahoma City/Norman, Oklahoma
SGF - Springfield, Missouri
SHV - Shreveport, Louisiana
SLC - Salt Lake City, Utah
TOP - Topeka, Kansas