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 Record cold February night across NSW
Records for low night temperatures fell at over a dozen places in NSW and a few in SA and VIC this morning as clear skies and dry air in the cold airmass that has dominated the southeastern states for three days allowed temperatures to plummet.
Canberra was the most notable new record, with a minimum of 2.8° ousting the old February record of 3.0°, set in 1962 and equalled in 1985 in a climate history that dates back to 1939. The record doesn't show up in the Daily Weather Summary list of records because the observation site was moved within the airport grounds in 2010, and the new location hasn't yet accumulated the 10 years of observations necessary for records to be verified for that location, but a comparison of the two sites before the old one closed down showed they were a good match.
This morning's 2.8° was a normal temperature for late May, so Canberrans would have needed their heavy duty doonas. Interestingly, it has been colder in January with the mercury down to 1.6° on 12 January 2012.
It has been an unusually cold period for February with this morning's NSW record lows scattered across all of the southern half of the state. Forbes and Yanco broke records set a day or two ago in the earlier stages of this unusually long run of record-breaking cold nights. Two surprising records were 6.9° at Victor Harbor SA and 8.1° at Cape Nelson Lighthouse in western VIC. Both locations are beside the sea, showing that the low temperatures are due to a cold airmass, not to localised inland cooling.
One other telling record was smashed at the Agricultural Institute at Orange NSW. Normal temperatures are recorded in a Stevenson screen, which is a specially louvred design to eliminate radiation heat from nearby objects and ensure that only the temperature of the air is being measured. The thermometers are exposed one metre above the ground. A special temperature recorded at a few weather stations is the grass or terrestrial minimum temperature, recorded by a thermometer exposed in the open at grass-tip level. It's the temperature you'd experience lying on the ground out in the open, and is often 5 to 7 degrees below the screen minimum on still, clear winter nights when the air is dry. Its main purposes are to show whether frost has occurred and the conditions experienced at the level of young crops. This morning, Orange had its coldest grass minimum temperature in its 39 years of such observations when the grass minimum sank to -3.8°, knocking 2.8° off the old record. (Note that this record has not yet been verified.)
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