Ferrell 18Z pressure 1981 - 987.7 989.3 992.8 984.5 978.4 986.5 994.8 989.0 980.7 977.3 978.6 1982 989.9 986.2 977.9 979.7 986.7 979.9 988.8 975.6 975.5 979.9 985.2 994.4 1983 991.9 994.4 985.2 979.1 984.9 988.6 980.8 - - - - - 1984 994.0 988.5 979.3 980.2 988.2 980.2 975.9 985.2 981.2 - - - 1985 - 989.0 986.9 987.8 988.9 - 975.5 986.1 975.6 976.4 - - 1986 - 993.6 991.1 981.7 992.5 992.2 981.1 984.2 979.4 974.0 975.7 981.7 1987 - 988.5 987.3 989.8 983.5 989.1 993.6 975.9 989.7 980.1 979.2 986.0 1988 988.9 985.5 986.4 984.8 991.0 994.9 978.2 975.1 984.5 991.1 981.7 982.5 1989 984.9 985.7 985.0 989.4 - - - - - 975.5 976.6 989.1 1990 988.3 983.2 986.9 993.9 999.7 989.3 998.9 982.6 973.7 983.4 985.0 984.8 1991 983.9 989.7 983.7 987.7 989.6 991.7 - - - - 985.3 995.5 1992 989.1 997.8 988.2 987.2 992.1 997.2 984.7 - - - - - 1993 - 977.6 985.6 980.8 982.9 976.3 972.4 977.8 976.7 976.3 978.9 982.2 1994 984.3 982.5 978.7 985.2 985.3 998.4 988.9 974.8 989.4 977.2 983.8 980.1 1995 980.2 980.7 991.0 983.7 980.3 988.7 1001.5 986.2 977.4 980.0 977.4 976.9 1996 985.6 990.1 985.1 978.4 985.8 981.9 983.2 987.6 989.1 972.1 986.6 984.9 1997 988.5 989.0 980.0 985.8 973.1 987.9 979.8 977.5 980.7 976.6 987.2 990.0 1998 985.2 980.4 982.1 975.8 982.2 977.9 980.6 - - - - - 1999 - 987.4 - - - - - - - - - - 2000 - - - - - - - - - - - - 2001 - 988.1 985.6 979.4 985.3 982.1 987.4 983.5 979.0 972.7 976.0 976.4 2002 983.2 977.7 990.6 980.7 992.6 994.7 989.4 979.1 986.3 989.8 982.9 978.5 2003 - - - - - - - - - - - - 2004 - - - - - - - - - - - - 2005 - - - - - - - - - - - - 2006 - - - - - - - - - - 978.7 982.5 2007 986.2 982.8 990.1 984.9 986.3 985.8 997.2 979.5 977.9 982.0 981.8 975.4 2008 979.7 979.9 984.5 985.4 983.3 977.0 980.1 982.8 971.7 974.2 - - 2009 - - - - - - - - - - - -