Tim Bach

Rainfall in May was well below average because of a “blocking high” pressure system which persisted over south eastern Australia for most of the month.

Rainfall recorded by the Bureau at the Daylesford weather station was 45.4 mm for the month compared to the long term average of 65 mm. And if it was not for 32.4 mm recorded on the last day of May, it would have been the lowest monthly rainfall in 80 years.

A “blocking high” is a high pressure system which tends to remain in place and blocks the normal west to east flow of weather systems across the Australian continent. It brings clear skies, sunny days, cool and sometimes frosty nights and often morning fog. A blocking high has persisted off the South Australian coast for most of the month of May and brought clear, stable weather to south eastern Australia.

Daily average temperatures measured at the Ballarat aeroderome (the nearest station that records daily temperatures) were 16.8°C, well above the long term average of 13.7°C.

Local higher temperatures reflected global average temperatures for May. According to a report from scientists at Climate Central, May was the hottest month on record and was the twelfth month in a row that the monthly record had been broken. Every country in the world experienced more extreme heat days than normal over the past year. Australia was one of the least affected countries with 35 days of extreme heat (days with maximums greater than the 90th percentile), 17 more extreme days than normal.

The dry weather has impacted water storage levels. Daylesford’s total water storage is at 64% of capacity, down 7% from last month and well below the 91% recorded at the end of May last year.

The Bureau has declared a La Nina watch because of ocean surface temperatures in the central Pacific Ocean. This does not mean a La Nina exists but indicates that 50% chance that it could develop. There is a 50% chance that conditions will remain neutral. A La Nina is associated with above average rainfall over south eastern Australia.

Vistor Szwed, our regular weather columnist, is travelling overseas and Tim Bach is filling in while he is away. Tim is a Daylesford resident and the editor of The Wombat Post.