Sydney achieves rare temperature yo-yoBrett Dutschke, Monday October 14, 2013 - 16:14 EDT
Sydney has cooled by at least 14 degrees twice in three days, for only the second time on record.
Today (Monday) was 14 degrees cooler than yesterday (Sunday) and last Friday was 15 degrees than previous day (Thursday).
It has been t-shirts one day, cardigans the next.
Maximum temperatures have gone from 37.3 degrees last Thursday to 22.2 on Friday then shot up to 35.0 degrees on Sunday and fell back down to 20.7 on Monday.
In 154 years of records the only other shorter turnaround of two extreme temperature changes was in 1977.
In late summer that year the temperature dropped by more than 18 degrees only two days after dropping by more than 15 degrees. Between January 30th and February 2nd Sydney's maximum went from 40.4 degrees to 25.7 to 41.4 to 22.8.
The reason behind this recent extreme temperature yo-yo is cold fronts becoming strong after having been so weak for so long.
During winter and early spring weaker-than-normal cold fronts allowed the air to become hotter than normal over central Australia. The fronts had only recently become stronger, so were able to draw the heat to the coast before bringing colder changes. We managed to get two strong cold fronts in the space of just three days.
The Southern Annular Mode (SAM) has only recently become strongly negative for the first time since 2004, giving cold fronts more intensity, leading to wild temperature fluctuations.
The latest trend in the SAM is indicating that fronts will become weaker during coming few weeks, leading to smaller temperature fluctuations and most likely a reduction in severe fire weather days.
Last Sunday fire danger was at its highest level in three years or more for parts of Sydney, the Hunter and Mid North Coast.
© Weatherzone 2013
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