"Philip Eden" philipATweatherHYPHENukDOTcom wrote in message
...
"Norman Lynagh" wrote
I don't have up-to-date figures immediately to hand but the 1931-1960
rainfall averages (mm) for June/July/August in your neck of the woods
a
St Mary's (Scilly) 49 61 64
Bude 48 72 75
Exeter 48 55 69
Falmouth 58 72 77
Hartland Pt 50 76 83
Ilfracombe 56 82 92
Newquay 47 72 70
Plymouth 53 70 77
For 1931-60 June was clearly the driest of the 3 summer months. There may
well have been a change in more recent years - Figures anyone?
July has become much much drier since about 1970, and August has
followed suit to a more limited extent. The change is evident in all parts
of the UK but is strongest in southern England.
Decadal averages for E&W are as follows (in mm):
Period June July Aug
1931-40 61.0 85.9 59.7
1941-50 56.9 70.0 89.8
1951-60 66.9 79.3 98.7
1961-70 61.3 72.1 84.8
1971-80 66.4 57.9 74.8
1981-90 68.5 56.8 71.4
1991-00 69.3 57.1 70.8
1995-04 67.7 59.2 76.5
Based on 30-year means in the EWP series, July was the wettest
month of the year (yes, wetter than Oct, Nov, or Dec) between
1801-30, but was the driest month of the year in both 1961-90 and
1971-2000. No other month has appeared at both extremes.
Also, July rainfall for overlapping 30-year periods was consistently
between 85 and 90mm for about almost a century until the 1850s,
over 50% above its recent level. No other month has varied that
much (although March has come close).
The drying out of July and August is consistent with some climate
change model predictions ... until we remember that it began at the
coldest point in the mid-20th century Micro Ice Age (that is, within
two or three years of the maximum ice extent in the Iceland/
Greenland region), and clearly has stabilized or even reversed since
the late-1980s when the warming of July and August became so
apparent.
If you look at http://www.climate-uk.com/indices/06.htm it seems
that June rainfall varies inversely with June westerliness, which may
appear
counterintuitive ... however, the decade to decade variations are really
very small and a single wet or dry month can make the difference between
a relatively wet decade and a relatively dry one.
http://www.climate-uk.com/indices/07.htm suggests the opposite,
until you look at the pressure line which ties in well with low pressure
and plentiful rain in the 1930s, and relatively high pressure from
the early-70s until recently.
http://www.climate-uk.com/indices/08.htm also indicates a loose
tie-in between mean decadal sea-level pressure and August rainfall.
Philip Eden