Page:Hunt - The climate and weather of Australia - 1913.djvu/104

Rh In January, the rain smears extend usually over the three gold-fields. They occur nearly always when a low lies off North-west Cape—the high being to the south-east, either over the Bight or further east. The wind is generally from the north—east, but if the southern high is rather to the west then south winds also bring rain to the fields.

In February, the conditions are much the same. The rains in the north (Pilbara) usually accompany north winds in front of the low, and those in the south south or south-east winds in front of the high. There is a strong tendency for the low to "sit" over the north of the high in this month, when rain is probable.

In March—The above conditions obtain also in March, but in addition rains with south winds occur sometimes with a low south of the Leeuwin and a high advancing on Geraldton (vide 2nd March, 1912). The southern cyclonic eddies are now moving north and affect the continent.

In April, the second type of rain-bringer is prevalent, i.e., a low south of Leeuwin and a high approaching Geraldton. Winds are northerly first, and then southerly as the low advances. Coolgardie rains are due usually to the latter winds.

In May, the favorable condition for rain appears to be when two highs lie rather near together ("A" over South-eastern Australia and "B" off Geraldton), with a low just south of Cape Leeuwin. The winds are northerly and the rain smear chiefly in the south.

In June, conditions are much the same. The first high lies over Central and East Australia, the second approaches North-west Cape, while the low lies off Cape Leeuwin. The accompanying winds (north-east and then south-west) both lead to rains, though in this month the southern winds affecting Coolgardie region are of increasing importance.

Variation in the position of the preceding high does not seem to be of such importance as gradient. For instance, in June, 1912, the gold-fields experienced a dry spell, although the conditions as stated above recurred about once a week as usual:—

June, 1912.

This summary shows that increased gradient (implying stronger winds) is apparently the most favorable factor in supplying Coolgardie with rain; for the velocity and path varied without effect.