Adelaide's daytime warmth keeps chill away at nightBrett Dutschke, Thursday April 11, 2013 - 18:54 EST
Many South Australian residents have been holding off heating their homes due to the late arrival of the autumn chill.
During the past week, days have had an average of 10 hours of sunshine and been warming to an average of 28 degrees, five degrees above the April average.
The warm, sunny days have allowed homes to stay reasonably warm at night when it cools down outside.
Most nights have been fairly cool, dipping below 15 degrees, but the city has yet to cool below 10 degrees.
Cooling below 10 degrees or a forecast of under 10 degrees is what many consider as the time to get the heater fired up.
The current forecasts suggest a night cooler than 10 degrees may still be a fair way off.
A cold front will bring an end to the run of warm days on Sunday, heralding much cooler weather, which will last much of the next week.
Days and nights will cool below the April average of 23 and 12 degrees respectively.
If it fails to cool below 10 degrees by next Wednesday this will be the latest it has done so in autumn in six years. In 2007 it took until the 10th of May to cool below 10 degrees.
Cooling below 10 degrees for the first time typically occurs in early April. Apart from 2007 you need to go back to 1976 to find the last time it took as long as this year to get this cool, the 20th of April.
The main causes are the clearer-than-normal skies over the inland, warmer-than-normal waters off the coast and a lack of strong cold fronts.
This has led to an unusually long run of warm days for this time of year. Saturday will be the ninth consecutive day of 26 degrees or warmer. It will be the first time in 42 years since this has happened in April. In 1971 there was a run of 15 days this warm.
On the rain side of things, the cooler change will only bring light rain to some parts of the city, generally only about five millimetres or less. This will be too little to get some gardens and parks green again and and also do little to raise dam levels.
Adelaide's catchment is about to drop to its lowest level in five years. As of today the catchment was holding 86880ML, less than 45% of capacity. When it falls below 86639ML in the next day or so it will be at its lowest level since winter 2008, when it dipped below 85000ML.
Unfortunately for Adelaide's catchment, the coming rain will favour northern areas, where there is potential for 20mm or more. This sort of rain is most likely over parts of the Eyre Peninsula and Flinders.
© Weatherzone 2013
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