Weather Watch | Expect butterfly effect

POTENTIAL: Forecast warmer June weather may be an indicator of heavier rains on the way in June and in mid- to late-July.
POTENTIAL: Forecast warmer June weather may be an indicator of heavier rains on the way in June and in mid- to late-July.

There have been several recent weather extremes which are interesting to note. These will have some effect on our regions in the next few months.

Sydney completed its driest April to May period with only 46mms since 2004 when 41mm fell.

Other marked dry April to May periods occurred in Sydney in 1859, 1885, 1888, 1942, 1954, 1957 and 1982. Out of all these past cases only 1942 resembled this year across the nation when record rainfall occurred in the Kimberley region of WA and also very heavy rain at Darwin during the wet season.

There was heavy rain late May of 1942 in our region and more of the same throughout the winter. May this year stayed very dry north from Condobolin, but heavy rain is anticipated in both June and July in our regions. Coonabarabran, with only 5.9mm this April and May, had its driest such period since 1923 when only 3.0mms fell.

Other very dry April-May periods at Coonabarabran were 4.8mms in 1912 and 5.0mm in 1902. The April- May period of 1897 was 23.4mm and all of that fell on May 31 1897. In fact there was no rain for 88 successive days at Coonabarabran from March 4 to May 30 1897.

The April-May period this year at Coonabarabran was the warmest also since 1897. The mean maximum temperature for April was 27.7 and for May was 21.4 compared with 27.4 and 22.9 respectively in 1897. The rainfall records for our regions show the 1897 winter and early spring to be wetter than average with the heaviest rains in June and July.

I was at Bendigo last weekend which had above-average rainfall for May as a result of heavy rain and thunderstorms on May 29. There were thunderstorms at nearby Maryborough which also had above-average rain in May. Both Bendigo and Maryborough have had their warmest January to May period this year since 1908.

That year was very dry from January to late May at both places; then heavy rain arrived near the end of May and continued right up to September of 1908, but with maximum temperatures falling to below normal.

Wangaratta last month completed its eighth successive month with the mean maximum temperature above normal.

The last time this happened was from October 1990 to May 1991. The period June 1991 to September was very wet at most places especially June when 142mm fell.

June of 1991 was also considerably warmer than normal, the warmest June since 1967.

This warmth looks like happening this June also with significant rain the second and fourth week of the month. Heavier rains are expected near mid-July and during the fourth week of July.