Australian Monthly Climate Summary: April 2009
Friday, 1 May, 2009
April 2009 was slightly warmer and drier than average for Australia as a whole. Most of the major population centres of the southeast, however, ran counter to this overall pattern with a month that was wetter or cooler (or both) than average, largely as a result of a major low-pressure system and associated cold outbreak in the final week. Mountain areas were particularly cold during this period and an Australian record low temperature for April was set.
Temperatures were mostly near or below normal in the south-east, and generally above normal elsewhere. National maximum temperatures were 0.56°C above normal (20th highest on record), and minimum temperature 0.37°C above normal (23rd highest), with no state or territory ranking in the top or bottom 10 for either.
Maximum temperatures were below normal in most of Tasmania, NSW away from the far west, and southern and eastern Victoria (except west Gippsland), but anomalies only reached −1°C on the high peaks of the Australian Alps. They were also below normal in western South Australia and the southeast of Western Australia, with anomalies of 1−2°C on the Nullarbor.
Most other areas were above normal. The western parts of Western Australia, west of a Carnarvon-Southern Cross line, were at least 1°C above normal with anomalies of 2−3°C commonplace, especially around Perth. Much of the northwest north of a Port Hedland-Alice Springs line was also at least 1°C above normal, locally reaching 2°C in the western Northern Territory and parts of the Top End, and 1°C anomalies were also scattered through eastern Queensland. Most of the Kimberley and adjoining areas of the Northern Territory, as well as an area around Perth, were in the highest decile.
The southeast also saw the largest area of below-normal minimum temperatures. Much of western Victoria was 1−2°C below normal, and negative anomalies extended to cover most of that state apart from its far east, as well as south-western NSW, south-eastern South Australia and parts of Tasmania. A major contributor to these anomalies was the cold outbreak that occurred in the final week of the month, especially at high elevations. Charlotte Pass (−13.0°C) set an Australian record low for April on the 29th, while on the same day Mount Hotham (−8.2°C) set a Victorian record and Liawenee (−7.5°C) narrowly missed the Tasmanian record.
Some other areas were slightly below normal, most significantly in interior northern Queensland and the southern interior and south-west of Western Australia, but most of the rest of Australia had slightly warmer nights than normal. The largest anomalies were in the northwest and the southern Northern Territory, reaching 1−2°C in places, while similar anomalies were scattered through eastern Queensland and NSW.
* Anomaly is the difference from the long-term average
Australian rainfall was 20% below the long-term average (52nd lowest of 110 years). All states and territories except for New South Wales (3% above) were below average, but only the Northern Territory (58% below) and Western Australia (45%) were more than 15% below average, and no state or territory ranked in the top or bottom 25% of years.
Rainfall was above average in significant parts of the southeast, including most of the agricultural areas of South Australia (extending into the far west and the Flinders Ranges), the south, and north coast, of Tasmania, the southwest coast and far northwest of Victoria, and the NSW tablelands and ranges (extending into far northeast Victoria), along with that state’s coast from Nowra northwards. Anomalies in this region, however, were mostly modest, with only the northern NSW coast and adjacent ranges between Newcastle and Grafton reaching the highest decile.
Outside the southeast, rainfall was also above normal in most of Queensland east of a Townsville-Longreach-Thargomindah line (except for a band running south from Rockhampton), reaching the highest decile in the Brisbane/Sunshine Coast region, which saw significant flooding early in the month. Above-normal rains also covered north-western Queensland and adjacent eastern parts of the Northern Territory, and the south-eastern quarter of Western Australia.
April, which normally sees the first significant winter rains in the southwest of Western Australia, was a very dry month in that region, ranking as the ninth-driest on record (79% below normal). Most of the region bounded by Perth, Southern Cross and Albany was in the lowest decile, as was the coast around Geraldton and Shark Bay. It was also a dry finish to the wet season in much of the northwest, with little rain in the Kimberley or the Northern Territory except for the northern Top End and areas bordering Queensland.