In my report for May 2009 I included data on air frost and how the occurrence of below zero temperatures had changed over the years since my records began in 1984. I have now analysed the pattern for the first frost at this time of year. To see the trend more clearly I have analyzed the data over five-year periods and the average for each period is in the table below, both for Spring and Autumn. Although the warming in Spring is evident from 1985, this trend for Autumn didn’t start until the late 1990’s. For both periods there is now a shift of around one month, for these average figures.
|
1985 – 89 |
1990 – 94 |
1995 – 99 |
2000 – 04 |
2005 – 09 |
|
| Last Frost of Spring |
14th May |
11th May |
5th May |
26 April |
22nd April |
| First Frost of Autumn |
29th Sept. |
22nd Sept. |
9th Oct. |
18th Oct. |
26th Oct. |
The trend in the total degrees of air frost for each month since 1984, November & December 2009 excluded, also produces interesting data, as in the table below. November and particularly December during this period, show an increasing severity of air frost in contrast to the less severe monthly frost totals at the beginning of the year.
|
January |
February |
March |
October |
November |
December |
|
-8° |
-10° |
-3° |
-1° |
+3° |
+20° |
