Subtropical Virginia

L. David Roper
http://www.roperld.com/personal/roperldavid.htm
 16 July, 2017

Introduction

There are several definitions of "subtropical" regions of the Earth:

The following map shows the long-standing subtropical regions:

Richmond, Virginia and Virginia Beach, Virginia are subtropical.

Roanoke and New River Valleys of Virginia

2009

I have been wondering if the New River and Roanoke Valleys of Virginia are now subtropical due to global warming, according to the definitions given above. The data are available at http://www.weather.gov/climate/index.php?wfo=rnk . I calculated the average monthly temperatures by averaging the average monthly highs and lows for 2009, the latest year for which all months are available. The results for Blacksburg in the New River Valley and Roanoke in the Roanoke Valley are:

2009
Blacksburg
Roanoke
Jan-09
30.95
36
Feb-09
35.95
42.2
Mar-09
43.3
48.3
Apr-09
52.55
57.5
May-09
61.9
65.35
Jun-09
69.35
74.1
Jul-09
68.4
73.3
Aug-09
71.4
76.05
Sep-09
63.6
68.75
Oct-09
52.25
57.25
Nov-09
45.8
51.5
Dec-09
32.6
37.25

We see that

Thus, Roanoke fits 2 of the 3 different definitions for being subtropical in 2009 and Blacksburg fits 0 of the 3.

2006

The earliest year for which all months are available on the web site is 2005. The results for that year are:

2006
Blacksburg
Roanoke
Jan-06
39.85
43.55
Feb-06
34.7
39.55
Mar-06
43.45
48.6
Apr-06
56.3
60.85
May-06
57.7
63.35
Jun-06
67.1
72.2
Jul-06
72
77.55
Aug-06
72.3
78.35
Sep-06
60.95
65.15
Oct-06
50.9
55.4
Nov-06
45.95
50.3
Dec-06
39.35
45.05

We see that

Thus, Roanoke fits 3 of the 3 different definitions for being subtropical in 2006 and Blacksburg fits 1 of the 3.

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Roanoke, Virginia

The data for Roanoke, Virginia for 2006 and 2009 were intriguing, so I put together all four years for Roanoke available from the Blacksburg weather station, since climate is averaged over many years. The result is:

Roanoke:
Year
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
subtropical
2006
43.55
39.55
48.6
60.85
63.35
72.2
77.55
78.35
65.15
55.4
50.3
45.05
50
2007
41.2
34.2
53.15
55.95
67.55
74.4
75.65
82.15
71.5
63.55
48.3
43.45
50
2008
37.5
41.6
49.4
57
64.2
75.9
76.05
74.15
69.65
58.15
45.95
41.8
50
2009
36
42.2
48.3
57.5
65.35
74.1
73.3
76.05
68.75
57.25
51.5
37.25
50

The first subtropical definition is true for three of the four years.

After I had done the work described above, I was informed that data for many more years were available at http://www.sercc.com/cgi-bin/sercc/cliMONtavt.pl?va7285 . These data were already given as monthly average temperatures. The data are shown in the Appendix. The last ten years' data are:

Year
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
 T>50
2000
35.3
43.4
51.7
54.86
67.63
73.78
73.29
72.85
65.87
59.4
44.15
30.4
8
2001
36.9
42.9
43.35
59.45
64.79
73.32
74.31
76.85
66.45
56.9
53.1
43.4
8
2002
42
40.9
48.16
58.77
63.95
74.48
78
76.95
70.67
57.6
46.22
37.7
7
2003
33.1
35.7
49.58
56.82
62.55
69.53
75.13
76.35
66.72
56.1
52.2
37.9
8
2004
34.6
38.5
50.2
58.08
70.76
72.25
76.5
73.39
69.1
59.3
51.4
39.5
9
2005
40.5
41.7
44.06
56.72
62.23
72.73
77.76
77.6
71.15
60.2
49.85
36.8
7
2006
43.5
39.6
48.61
60.83
63.34
72.22
77.53
78.34
65.15
55.4
50.3
45.1
8
2007
41.2
34.2
53.2
55.95
67.56
74.42
75.66
82.15
71.5
63.6
48.3
43.4
8
2008
37.5
41.6
49.4
56.98
64.19
75.9
76.06
74.15
69.65
58.2
45.95
41.8
7
2009
35.9
42.2
48.32
57.48
65.35
74.08
73.31
76.06
68.77
57.3
51.5
37.3
8

Seven of the last ten years had 8 or more months above 50.0 °F.

Data for years 1949 to 2009 are:

Note the linear trend lines for March and November, the two crucial months, whose equations are given above the legend. November leads March in temperature. Using those equations:

If the linear trend continues, after about 2030 all years in Roanoke, Virginia will be subtropical by the first definition.

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Blacksburg, Virginia

Data are also available from 1953 to 2009, with a few missing years, for Blacksburg, Virginia.

Data for years 1949 to 2009 are:

According to this data set there are no subtropical years for Blacksburg from 1949 to 2009. (Apparently my method of averaging the average monthly high and average monthly low is not the correct way to get the average monthly temperature.) Note that the linear trend lines for March and November have a long time to go before crossing the 50.0 °F value; November would have that value at about year 2190.

So, Blacksburg is NOT near to being a subtropical region by the first definition.

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Richmond, Virginia

Since Richmond, Virginia is listed as a subtropical region, I show here the monthly average temperatures from 1949 to 2009 for Richmond:

Note that when November is less than 50.0 °F March is often above 50.0 °F, such that 16 of the 20 years from 1990 to 2009 were subtropical by the first definition. The trend line for November crosses the 50.0 °F line at about 1990.

Note the linear trend lines for March and November, the two crucial months, whose equations are given above the legend. November leads March in temperature. Using those equations:

If the linear trend continues, after about 1990 all years in Richmond, Virginia are or will be subtropical by the first definition.

Go to the top.

Average Annual Temperatures

The following graphs show the average annual temperatures for Blacksburg, Roanoke and Richmond VA since about 1950 to 2009:

Note that all three locations show global dimming due to the huge amount of aerosol pollution burning fossil fuels was putting into the atmosphere before clean-air legislation (1960-1970 UK, 1970 US) reduced the pollution and allowed global warming to take over again.

This is similar to what occurs for the global average annual temperatures:

Conclusion

Roanoke, Virginia in the Roanoke Valley is well on the way to being a subtropical region.

Blacksburg, Virginia is NOT on the verge of being a subtropical region.

Richmond, Virginia has been a subtropical region since about 1990.

Appendix: Average monthly temperature data for Roanoke, Virginia from 1949 to 2009

YEARS
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
ANN
Months >50
1949
44.8
44.1
46.1
53.29
65.02
73.65
77.26
73.16
64.85
61.5
47.13
40.4
57.6
7
1950
47.5
40.3
42.58
53.65
65.23
71.35
73.16
72.26
65.77
60.9
43.22
34.5
55.87
7
1951
38.4
39.8
45.4
54.45
64.23
72.83
76.03
75.66
68.12
60.3
41.18
38.4
56.23
7
1952
42.1
42
45.1
56.3
65.15
77.77
78.31
73.34
66.82
54.4
47.45
39.5
57.35
7
1953
41.5
42.5
47.61
55.22
70.87
74.55
78.34
76.76
68.8
60.8
47.65
39.1
58.65
7
1954
37.4
43.9
45.53
60.53
60.68
73.48
77.53
75.69
71.85
59.2
43.03
36.9
57.14
7
1955
35.3
39.4
48.34
60.12
67.69
68
79.77
77.13
68.72
58.1
44.53
34.2
56.77
7
1956
35.3
42
45.92
53.58
65.69
72.23
76.24
75.68
66.77
58.9
45.58
47.8
57.14
7
1957
35.7
43.4
45.4
59.75
67.61
73.7
76.44
73.66
68.53
53.5
48.12
41.1
57.23
7
1958
33.4
31.8
41.29
55.82
64.61
71.78
78.15
75.02
68.13
57
50.33
34.2
55.12
7
1959
36
40.9
45.45
58.5
68.73
73.73
77.08
79.05
70.3
59.6
44.75
41.1
57.92
7
1960
38
36.5
33.97
60.13
63.16
73.02
75.87
77.69
69.62
58.7
47.7
32.3
55.56
7
1961
33.2
41.1
50.05
51
61.44
71.3
76.56
75.56
71.88
58.3
49.23
37.2
56.4
7
1962
35.6
40.1
43.5
53.75
69.92
72.37
74.16
74.34
64.82
59.4
45
33.3
55.53
7
1963
32.9
32
49.66
58.6
64.42
72.85
74.94
73.85
65.98
60.5
48.57
30.5
55.39
7
1964
37.3
35.5
46.47
56.83
67.31
74.62
75.85
73.95
66.82
54
51.13
40
56.65
7
1965
36
36.4
41.89
54.9
69.19
69.72
73.84
74.19
69.65
55.9
47.47
41.5
55.89
7
1966
30.6
35.1
46.66
51.45
63.26
71.08
77.82
73.02
66.02
54.6
47.17
37.8
54.53
7
1967
40.8
34.8
48.45
58.98
58.97
70.23
73.39
72.58
63.22
54.7
43.33
41.3
55.06
7
1968
33
33.8
51.27
56.48
62.37
71.25
75.61
75.24
66.72
57.4
48.05
33.7
55.4
7
1969
32.3
37.2
40.65
57.27
65.02
73.07
75.94
73.47
66.65
56.6
44.53
33.6
54.69
7
1970
29.7
36.8
42.44
56.52
66.74
72.85
76.11
74.03
72.58
59.7
46.28
40
56.15
7
1971
33.8
39.1
43.58
55.42
61.47
72.62
73.52
72.56
69.8
62.1
45.33
45.3
56.21
7
1972
39.6
36
45.58
55.5
61.98
67.63
74.29
73.16
67.58
52.1
45.4
44.5
55.28
7
1973
37.2
35.7
51
53.8
61.08
73.75
75.45
75.95
70.73
59.2
49.33
38.1
56.78
8
1974
45.2
39
50.7
57.15
64.29
68.1
74.48
73.42
64.78
55
47.25
38.9
56.52
8
1975
39.6
40.4
42.19
52.87
66.45
71.5
74.47
76.98
66.53
60
51.07
38.7
56.73
7
1976
33.4
46.7
50.8
57.4
62.24
70.02
73.92
72.08
65.13
50.2
40.18
34.2
54.7
8
1977
23.6
36.6
52.5
58.85
68.05
71.12
79.69
77.73
70.38
53.6
48.52
35.8
56.37
8
1978
27.8
29.5
44.15
56.27
63.71
72.68
75.98
77.44
71.38
54
49.43
39.5
55.15
7
1979
31.3
29.3
48.63
55.67
63.79
69.32
73.45
73.98
66.32
54.6
49.57
40.9
54.74
7
1980
37.4
34
43.52
56.7
64.77
70.02
78.05
76.79
71.47
55.4
45.38
38.7
56.02
7
1981
32
38.2
43.1
58.53
60.92
73.97
76.08
73.37
66.1
53.7
45.17
32.8
54.49
7
1982
28.7
37.8
44.82
50.77
67.48
70.12
75.45
72.32
65.73
57.4
47.78
42.3
55.06
7
1983
35.6
36.5
46.95
52.37
61.02
70.05
77.02
77.9
68.1
57.1
47.07
34.9
55.38
7
1984
33.5
43.6
43.34
54.22
63.1
74.2
73.18
74.37
64.08
64.3
46
47.1
56.75
7
1985
31.2
38.6
50.2
61.82
67.05
72.63
76.47
73.81
68.35
60.3
55.42
35.1
57.58
9
1986
35.2
38.3
47.13
58.77
63.85
74.13
78.81
72.39
68.92
58.9
47.37
38.5
56.86
7
1987
34.2
36.9
46.6
53.23
67.1
74.93
79.24
77.79
68.85
51.5
49.57
41.4
56.77
7
1988
30.7
37.9
47.48
55.33
63.34
70.93
77.05
77.45
65.97
51.2
46.68
38.9
55.24
7
1989
41.3
38.2
47.35
54.25
61.15
73.68
75.89
74.05
68.05
58.4
46.02
29.5
55.66
7
1990
43.6
45.9
51.5
56
64.23
72.55
76.84
74.55
68.32
59.2
52.1
43.7
59.04
9
1991
39.3
42.7
49.18
57.5
69.6
73.52
77.85
74.77
69.32
59.4
46.8
42.3
58.52
7
1992
39.6
41.5
46.48
55.48
60.16
68.37
76.94
72.06
67.92
55.5
46.32
38.5
55.73
7
1993
39.7
35.9
42.11
54.5
65.6
71.92
80.24
76.82
68.53
55.3
47.28
36.2
56.18
7
1994
30.5
39.4
46.69
60.92
60.53
75.05
77.53
73.92
66.85
56.6
51.4
42.9
56.86
8
1995
38.5
36.9
50.1
56.78
64.32
71.98
76.9
78.52
67.42
58.5
43.17
35.5
56.54
8
1996
33.6
38.2
41.61
56.3
65.16
72.75
74.4
73.37
66.08
57.9
40.97
40.1
55.04
7
1997
35.8
43
49.66
52.47
60.27
69.18
76.1
73.37
67.73
56.2
43.6
38.3
55.47
7
1998
41.2
42.2
45.76
56.5
67.11
73.47
77.45
75.87
73.57
59
48.92
43.4
58.7
7
1999
39.8
42
43.94
58.13
64.08
72.25
79.15
75.44
66.4
55.7
52.88
42.5
57.69
7
2000
35.3
43.4
51.7
54.86
67.63
73.78
73.29
72.85
65.87
59.4
44.15
30.4
56.06
8
2001
36.9
42.9
43.35
59.45
64.79
73.32
74.31
76.85
66.45
56.9
53.1
43.4
57.65
8
2002
42
40.9
48.16
58.77
63.95
74.48
78
76.95
70.67
57.6
46.22
37.7
57.94
7
2003
33.1
35.7
49.58
56.82
62.55
69.53
75.13
76.35
66.72
56.1
52.2
37.9
55.97
8
2004
34.6
38.5
50.2
58.08
70.76
72.25
76.5
73.39
69.1
59.3
51.4
39.5
57.79
9
2005
40.5
41.7
44.06
56.72
62.23
72.73
77.76
77.6
71.15
60.2
49.85
36.8
57.61
7
2006
43.5
39.6
48.61
60.83
63.34
72.22
77.53
78.34
65.15
55.4
50.3
45.1
58.32
8
2007
41.2
34.2
53.2
55.95
67.56
74.42
75.66
82.15
71.5
63.6
48.3
43.4
59.26
8
2008
37.5
41.6
49.4
56.98
64.19
75.9
76.06
74.15
69.65
58.2
45.95
41.8
57.61
7
2009
35.9
42.2
48.32
57.48
65.35
74.08
73.31
76.06
68.77
57.3
51.5
37.3
57.29
8

https://en.wikipedia.org/wiki/List_of_locations_with_a_subtropical_climate

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