During the past week a second low pressure trough formed near Charleville and extended southwards, bringing 36 millimetres to Thargomindah by early Friday morning, May 9, and then 53.2 millimetres to Griffith, 45.6 Deniliquin, 56 to Hay, 47 to Hillston and 39 to Cobar, all to 9am on Saturday May 11.
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None of this rain, apart from light falls, reached most of Victoria although an isolated heavy fall of 41.4 millimetres occurred at Mangalore, the wettest May day there since 2000. Griffith had its wettest May day in 110 years of records, while Hay and Deniliquin had their wettest May days since 1974. Both Cobar and Hillston, which had heavy falls on May 4, have now clocked up 101 and 118.6 millimetres for May respectively. It is the wettest May to date for Cobar since 2000 and the wettest ever May in 143 years of records at Hillston.
A very strong high pressure has been more or less sitting just south of Tasmania for all of May. A most unusual situation has been the occurrence of rainfall in Victoria when mean sea level pressures have been well over 1030 millibars. Melbourne recorded 14 millimetres of rainfall when the barometric pressure reached 1033 millibars. Even in Hobart light rain fell when barometric pressures reached 1038.6 millibars. For those who own a barometer set correctly at 1038.6 millibars, the dial would be right over "Very Dry". Back in 1955 I do remember very high barometer readings of well over 1035 millibars in Melbourne from late April through to July set up big rain events in NSW and Queensland. I was with my parents on a trip to the Riverina late in May 1955 when a very big high pressure was south of Melbourne and a massive rain event was invading the Riverina as we drove southwards in our old 1934 Dodge car, which I found to be a gem to drive over 100 miles in one day.
Minimum temperatures above normal
Most of our region except northern Victoria, which has been notably dry the past four weeks, has seen a lack of morning frosts with mean minimum temperatures being more than five degrees above the May normal. The mean minimum temperature for the first fortnight of this May in Coonabarabran sits at 9.2 degrees, more than six degrees above normal and the warmest in May for 35 years. The first frost in May 1989 did not arrive in Coonabarabran until May 24, the latest date on record. This May could come close to the latest date of frost occurrence. The 38 millimetres of rainfall in Coonabarabran to Saturday, May 11, was the wettest May day since 2007 and the month's total has exceeded the average for the second successive month. Other notably high minimum temperatures during the month of May in Coonabarabran were in 1983, 1963 and 1889 and to a lesser extent in 1938 and 1942. Out of these, late May to mid July was very wet in our regions. Later on, November turned out to be very wet with a high frequency of thunderstorms.
There have been 10 days of frosts in North East Victoria at Wangaratta and Rutherglen, but quite different across the border into the Riverina where all places including Albury have had not a single frost up to May 14. Mean minimum temperatures across the Riverina to date were two degrees above the May normal, not as great further north.
The strong high pressure has now weakened at present; this does indicate to some extent not much rainfall in our region for nearly two weeks. The next significant rain is expected to be around the last weekend of May and again during the first week of June.
