Jökull - 01.12.1988, Side 65

Fig. 4 Average annual precipitation 1931-1960 in southwestem Iceland (mm).
Mynd4. Meðalársúrkoma suðvestanlands 1931-1960 (mm).
two weather stations, Reykjavík and Eyrarbakki,
located on each side of the Reykjanes mountains.
Highest monthly values occur in October while May
and June are the driest months of the year.
As an average for the country as a whole
October’s share of the annual precipitation is about
12% and that of May about 5%. This is in agreement
with the fact that average surface pressure is usually
highest in spring but lowest in early winter.
The fact that precipitation is larger in early winter
than late winter can at least partly be explained by
the fact that temperature is higher in the former
period and consequently the moisture content too.
Monthly values of precipitation show large year-
to-year variation and months with no precipitation at
all exist.
Fig. 4 shows the distribution of annual precipita-
tion 1931-1960 in southwestem Iceland. As a large
part of the precipitation falls with winds between
east and south, which prevail in the forward part of
cyclones arriving from the southwest, it is to be
expected that the highest precipitation values are
found windward and in the mountains, with decreas-
ing values on the leeward side. This is confirmed by
the distribution. Values of 3000 mm or more are
found in the mountain areas. The values decrease to
800 mm in Reykjavík which, because of the rain
shadow, is the minimum area of the investigated
region. From Reykjavík there is consequently a
rapid increase in precipitation towards the
JÖKULL, No. 38, 1988 63