Jökull - 01.12.1988, Page 67

CLASSIFICATION OF MAIN
WEATHER TYPES IN ICELAND
The author has earlier presented a classification of
main weather types in Iceland (Einarsson, 1976,
1984). Cyclones are frequent in the vicinity of Ice-
land, especially in winter, and the weather depends
to a great extent on the tracks of such systems. It is
clear that for each weather type, the weather will
differ considerably from one part of the country to
another, depending on the weather system in action,
wind direction and topography. The classified
weather types are supposed to describe the main
characteristics of the weather. Although they are, in
a subjective way, mainly based on the author’s
experience, investigations have already shown that
each type shows distinct characteristics different
from the other types (Einarsson, 1983). Conse-
quently the classification seems to be an usable tool
for this purpose.
Six out of eight classified weather types may be
expected to result in precipitation in one part of the
country or another. These are (Fig. 6):
a) southeastern, b) southwestern or western,
c) southern with warm air mass, d) eastern,
e) northeastern, f) northern.
By selecting days from 09h GMT to the same
time next day matching one of these weather types,
it is possible to take a closer look into different
weather elements for each weather type. In the fol-
lowing the distribution of the number of days with
precipitation in Iceland and the amount of precipita-
tion in southwestem Iceland will be described. By
going through all weather charts for a 5 years
period, 30-54 days for each weather type were
found, except in one case where only 18 days were
found. In each case the same weather type had to be
prevailing the whole day.
NUMBER OF DAYS WITH
PRECIPITATION IN ICELAND
IN DIFFERENT WEATHER TYPES
Figs. 7-12 show the distribution of the number of
days with precipitation of 0.1 mm or more for each
of the six weather types mentioned above, expressed
Fig. 6. Six classified weather types, which cause
precipitation in one part of the country or another:
a) southeastem, b) southwestem or westem,
c) southem with warm air mass, d) eastem,
e) northeastem, f) northem.
Mynd 6. Sex flokkar veðurlags, sem valda úrkomu í
einhverjum landshlutum: a) SA-átt, b) SV- eða V-átt,
c) S-átt með hlýindum, d) A-átt, e) NA-átt,f) N-átt.
in per cent of selected days. They are based on
values from 76 synoptic and climatological stations.
The figures show clearly how variable the number
of days with precipitation is, and how different the
distribution for each weather type is from the annual
one (see Fig. 5). In southwestem Iceland the number
is 80-100% in weather types southeastern,
southwestern or western and southern with warm
air mass (Figs. 7-9), except for the eastemmost
inland part, where values are lower than 80% in two
of them.
In general, frontal precipitation accompanies the
weather type southeastern. Southwestern or
western is a typical cold air mass weather type with
JÖKULL, No. 38, 1988 65