Schwerdtfeger 18Z temperature 1985 - -21.5 -26.3 -34.1 -34.2 -35.2 -46.9 -39.4 -36.3 -28.7 -18.8 -8.9 1986 -9.0 -17.3 -27.1 -30.4 -27.2 -36.1 -38.3 -41.5 -45.0 -29.7 -18.0 -9.1 1987 -7.0 -19.0 -34.1 -35.0 -32.6 -28.4 -35.4 -39.4 -37.2 -30.2 -20.2 -7.9 1988 -9.0 -20.0 -31.9 -31.3 -30.9 -32.3 -34.3 -28.1 -31.4 -23.2 -18.5 -8.1 1989 -7.8 -20.4 -27.4 -27.8 -34.0 -41.1 -35.9 -38.4 -36.3 -28.4 -14.1 -7.5 1990 -8.7 -20.4 -29.8 -31.3 -33.6 -36.5 -39.0 -41.7 -40.4 -32.0 -18.0 -6.8 1991 -8.9 -14.5 -31.3 -32.0 -34.0 -30.4 -39.0 -38.9 -30.4 -29.0 -17.5 -7.1 1992 -7.4 -20.8 -24.9 -36.2 -30.6 -37.0 -30.3 - - - - - 1993 - -20.5 -31.5 -32.1 -38.6 -32.2 - - - - -14.7 -8.9 1994 -7.6 -19.4 -31.3 -25.4 -39.0 -32.4 -34.2 - - - - - 1995 - - - - - - - - - - - - 1996 - -20.1 -31.9 -28.1 -36.5 -35.6 -37.9 -32.4 -32.9 -31.9 -17.2 -9.1 1997 -10.3 -22.7 -33.1 -36.7 -32.3 -33.5 -39.8 -41.4 -36.4 -24.9 -13.2 -9.5 1998 -11.7 -15.4 -29.5 -38.8 -34.8 -27.6 -38.6 -37.6 -41.4 -29.1 -19.5 -10.5 1999 -9.3 -21.4 -32.4 -39.5 -38.0 -38.7 -32.3 -41.9 -31.0 -27.7 -15.6 -10.3 2000 -11.7 -20.5 -27.4 -30.7 -33.1 -36.0 -33.9 -36.3 -38.3 -31.8 -14.2 -11.5 2001 -13.6 -17.7 -32.4 -32.0 -35.5 -33.1 -32.8 -47.1 -34.3 -31.5 -19.1 -9.5 2002 -9.6 -18.2 -25.3 -32.0 -31.4 -42.3 -43.3 -39.9 -32.1 -27.9 -18.0 -10.5 2003 -8.4 -20.0 -29.5 -35.2 -33.1 -33.4 -32.8 -39.7 -37.5 -25.7 -20.1 -8.4 2004 -10.6 -22.5 -33.7 -32.4 -38.3 -35.2 -48.2 -42.6 -41.0 -31.2 -15.6 -7.6 2005 -8.2 -19.7 -30.2 -32.9 -31.3 -36.0 -33.5 -37.9 -36.3 -26.9 -17.7 -7.3 2006 -10.0 -16.5 -29.4 -36.8 -40.5 -31.6 -41.2 -31.1 -32.6 -32.0 -18.2 -9.5 2007 -7.9 -17.1 -28.9 -31.8 -32.4 -33.8 -34.3 -35.6 -32.6 - - - 2008 - -19.0 -28.4 -30.2 -33.2 -28.6 -39.3 -46.2 -28.9 -27.0 -20.3 -8.6 2009 -9.3 -21.9 -31.6 -25.1 -36.7 -36.0 -35.4 -36.9 -37.5 -30.0 -13.6 -8.2 2010 -9.8 -18.1 -28.5 -30.4 -37.4 -38.1 -39.3 -37.7 -38.6 -27.9 -17.1 -8.4 2011 -9.1 -20.5 -27.7 -31.0 -31.8 -31.5 -28.2 -31.7 - - - -6.3 2012 -8.1 -16.4 - - - - - - - - - - 2013 - -18.2 -24.6 -37.3 -30.3 -37.2 -39.8 -37.4 -33.9 -28.3 -18.7 -9.6 2014 -9.6 -19.3 -28.8 -34.5 -30.1 -36.9 -41.7 -28.2 -27.1 -23.5 -20.7 -11.0 2015 -9.7 -14.5 -29.2 -35.3 -36.5 -34.9 -38.4 -36.2 -38.6 -28.5 -19.7 -10.4 2016 -7.0 -19.4 -29.2 -36.4 -33.6 -38.4 -40.4 -37.8 -38.0 -29.6 -18.6 -9.6 2017 -10.7 -20.9 -25.8 -26.9 -25.1 -34.3 -37.3 -31.2 -37.1 -26.5 -20.2 -10.2 2018 -9.5 -18.2 -24.3 -28.2 -34.4 -30.9 -37.4 -40.2 -35.5 -23.5 -16.0 -8.2 2019 -9.9 -16.3 -26.9 -31.2 -29.4 -32.1 -31.4 -33.4 -30.8 -28.4 -17.7 -8.0 2020 -9.5 -14.9 -28.8 -33.3 -30.8 -33.9 -35.2 -34.6 -34.1 -27.9 -20.1 -9.8 2021 -8.7 -18.9 -28.6 -39.6 -34.1 -33.5 -30.5 -44.4 -34.3 -27.6 -16.4 -8.8 2022 - -15.5 -25.8 -29.5 -28.4 -35.8 -30.1 -33.6 -33.8 -29.6 -22.2 -9.0 2023 -10.7 -19.2 -30.6 -33.2 -36.6 -32.3 -43.3 -44.0 -26.4 -29.0 -20.6 -9.9 2024 -9.9 -22.1 -29.0 -30.0 -33.7 -30.5 -36.2 -34.7 -39.8 - -20.2 -