Half-monthly Cet Values (extremes 1772-2011)

[Roger J Smith]

After downloading the data base of daily CET mean temperatures, I thought it might interest some to list the extreme half-monthly values since people often talk about half-monthly CET trends.

There may of course have been more extreme values in the period 1659-1771 particularly on the cold side, but we only have the daily values since 1772.

Now there may be some debate about what dates to assign to half-months, for the eight months that don't have thirty days. (April, June, September, November, no problem).

For the 31-day months, I arbitrarily chose 1-16 and 17-31 as my "half-months" and for February, which would normally be 1-14 and 15-28, I found it easier to tabulate 15-29 for leap years.

With that in mind, here are the extreme values of mean CET for each half-monthly period.

Extreme Highest CET means .... Extreme Lowest CET means ... 1981-2010 normal

JAN 01-16 ... 8.1 (2007) ; 8.0 (1873) .............. -3.7 (1814) ; -3.4 (1820) ... ... 4.4

JAN 17-31 ... 8.4 (1846) ; 8.1 (1804) ............... -3.7 (1776) ; -3.6 (1795) ... ... 4.5

FEB 01-14 ...8.8 (1869) ; 8.2 (1914, 2002) ...... -4.3 (1895) ; -2.2 (1855, 1917) ... 4.5

FEB 15-28(9) . 8.4 (1926) ; 8.3 (1846) ............... -2.6 (1947) ; -1.4 (1986) ... ... 4.3

MAR 01-16 ... 9.4 (1957) ; 9.2 (1961) ............... -0.6 (1845) ; 0.0 (1886,1947) ... 6.1

MAR 17-31 ... 10.2 (2005) ; 10.0 (1938) .......... 1.4 (1837) ; 1.7 (1853) ... ... 7.1

APR 01-15 ... 11.0 (2011) ; 10.5 (1926, 1943) ...... 2.6 (1917) ; 2.9 (1837) ... . 7.7

APR 16-30 ... 12.7 (1987) ; 12.6 (2011) .......... 4.5 (1808) ; 4.9 (1838) ... ... 9.3

MAY 01-16 ... 15.2 (1833) ; 14.3 (2008) .......... 6.9 (1902) ; 7.0 (1855) ... . 11.0

MAY 17-31 ... 16.1 (1992) ; 15.9 (1992) .......... 8.1 (1821) ; 8.3 (1891) ... . 12.4

JUN 01-15 ... 18.6 (1846) ; 17.8 (1822) .......... 10.6 (1916) ; 10.7 (1909) ... . 13.8

JUN 16-30 ... 18.4 (1976) ; 18.1 (1826) .......... 11.9 (1907) ; 12.1 (1823) ... . 15.1

JUL 01-16 ... 21.0 (1976) ; 19.8 (1983) .......... 12.5 (1879) ; 12.9 (1888,1907) ... . 16.4

JUL 17-31 ... 21.1 (2006) ; 19.6 (1995) .......... 13.4 (1841, 1883) ; 13.6 (1816, 1836) ... 17.0

AUG 01-16 ... 20.4 (1975) ; 19.8 (1995, 2003) ; 12.6 (1912) ; 13.1 (1812) ... 16.8

AUG 17-31 ... 19.3 (1955) ; 19.2 (1947) .......... 12.3 (1784) ; 12.4 (1890) ...... 16.0

SEP 01-15 ... 18.1 (1865) ; 17.3 (2005) .......... 10.8 (1807) ; 10.9 (1931) ...... 14.7

SEP 16-30 ... 16.5 (2006) ; 15.5 (1949) ............ 9,6 (1840) ; 9.8 (1889) ...... 13.4

OCT 01-16 ... 15.1 (1921) ; 14.9 (1949) ............ 6.4 (1888) ; 6.7 (1817) ...... 11.7

OCT 17-31 ... 13.1 (2005) ; 12.5 (2006) ............ 3.7 (1895) ; 3.8 (1926) ...... 9.6

NOV 01-15 ...12.0 (1938) ; 10.5 (1818, 1994) .... 2.3 (1919) ; 2.9 (1782) ...... 8.2

NOV 16-30 ... 9.6 (1994) ; 9.3 (1828) ............... 0.1 (1915) ; 0.5 (1815) ...... 6.1

DEC 01-16 ... 9.0 (1898 . 9.03, 1934 . 9.02, 1918 . 8.96) ... -1.3 (1879) ; -0.9 (1844) ... 5.0

DEC 17-31 ... 8.8 (1974) ; 8.6 (1987) .............. -2.3 (1874) ; -2.0 (1890) ... ... 4.3

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A few notes on the data, Dec 1786 had no daily data, the monthly mean of 2.8 appears for all 31 days. So we can't be too sure how it played out on a daily basis.

You may have noticed that the summer of 1911 did not register, it was about 3rd warmest in late July and early August. But the 32-day period 20 July to 20 August 1911 managed an average of 19.5 C, This compares favourably with various very warm summers.

The second half of December 2010 ranked third at -1.7 C.

Slightly different values would be derived if we always used 1-15 as the first half of all months.

Edited September 19, 2011 by Roger J Smith