Chance of late frost 21/06/06
The 30-day average of the SOI has risen over the last few weeks due to some strongly positive daily values to minus 1.9 as of Tuesday the 21st June. It will be very interesting to see if this upward trend is maintained or if it is just a short-term fluctuation.
As we have stated regularly, for there to be an overall widespread improvement in conditions across the state, it would help if the SOI went into positive values for a couple of months at least. The last time the SOI was in a "Consistently Positive" phase was for one month in March 2004 and before that was in early 2001.
Research has shown that the clear skies associated with a negative Southern Oscillation Index (SOI) increase the chance of earlier or later than normal frosts and may increase the number of frosts. On the other hand, those years with a more positive SOI are usually associated with more moisture and cloud as so are likely to have a shorter frost season and fewer frosts.
As there was a 'Consistently Negative' SOI phase at the end of May this year there is an increased chance of getting a later than normal finish to the frost season in Queensland. A negative SOI pattern has the potential to extend the frost season out by up to a couple of weeks.
Frost occurs with a combination of still cold air, clear skies and a dry atmosphere. In Queensland, these conditions can be usually found when a high-pressure system is approaching or passing in winter.
The local occurrence of frost is dependant on many factors including the terrain, soil type and plant cover. For example, frosts are more common in the bottom of valleys and hollows because cold and dense air travels down slopes. Dark soils are more prone to frosts than lighter coloured soils as they radiate heat at night more rapidly. Therefore local knowledge is important in pinpointing localised areas of high risk.
The latest rainfall probability maps for Queensland, Australia and the world are at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au
For more specific information for your location refer to Rainman StreamFlow or call the DPI Call Centre on 13 25 23 or (07) 3404 6999.