Australian Monthly Climate Summary: July 2007
Friday 3rd August, 2007
After the exceptionally cool June, Australian temperatures in July returned to more normal levels, with national averages slightly above the long-term normal. Also in marked contrast to June, seasonally dry conditions prevailed through most of the northern two-thirds of the continent, with little substantial rain away from the southern coast.
The Australian mean temperature for July was 0.34°C above the 1961−90 normal (24th highest of 58 years in the 1950−2007 period). Western Australia was very warm, experiencing its second-warmest July on record (anomaly +1.41°C), but Queensland was rather cool for a second successive month (−0.83°C, 7th lowest since 1950).
Daytime maximum temperatures were above normal over large parts of the country (national anomaly +0.78°C, 13th highest of 58 years), particularly in Western Australia (3rd highest on record) and South Australia (6th highest). Cool conditions were concentrated in eastern and northern parts of the country, with below-normal maxima covering most of Victoria, eastern inland New South Wales, the Darling Downs and most of tropical Queensland, the north-western Northern Territory and the Kimberley region. The most notable cool anomalies were in tropical eastern Queensland, reaching about −2°C around Cooktown, and mean maxima in the lowest decile covered much of this region, west to about Julia Creek and Normanton.
In contrast, it was significantly warmer than usual over large parts of central and western Australia. Anomalies exceeding +1°C, which ranked in the highest decile in most cases, covered most of extratropical Western Australia, the southern Northern Territory, South Australia north of Port Augusta and Ceduna, and adjacent parts of far southwestern Queensland and northwestern New South Wales. The strongest warm anomalies of +2 to +3°C (locally exceeding +3°C) occurred in much of the southern half of Western Australia, except for the southwestern corner.
National overnight minimum temperatures were very close to normal (anomaly −0.09°C, 22nd lowest of 58 years), with a cool east being offset by a warm west. Western Australia’s mean minimum anomaly (+1.15°C) ranked 4th highest on record, whilst Queensland’s (−1.40) was 10th lowest. The most extensive area of above-normal minima covered Western Australia (except for the Kimberley), with anomalies exceeding +1°C over most areas west of a Port Hedland-Wiluna-Esperance line, reaching +2 to +3°C in the western Pilbara and Gascoyne, the northern wheatbelt and the northern goldfields. Records were set over a region extending from the coast between Perth and Geraldton, inland as far as Kalgoorlie, whilst most of extratropical WA was in the highest decile. Elsewhere in the country there were only scattered areas where it was warmer than normal, the largest two covering eastern Victoria and south-eastern New South Wales, and the SA-Qld-NSW border region.
Cool anomalies covered much of the north and east. They were especially pronounced over eastern Queensland, where mean minima were generally in the lowest decile, with anomalies below −1°C east of a Mount Isa-Longreach-Goondiwindi line, and in the −2 to −3°C range in the southeast and between Mackay and Townsville. Records were set locally around Charters Towers. The middle of the month was particularly cold, with widespread frosts extending north to about the Tropic of Capricorn (as well as high-elevation areas west of Cairns), although few long-term stations set records. Brisbane Airport recorded its first sub-zero minimum (−0.1°C on the 19th), but has become more susceptible to extreme low minima in recent years because of site changes. Outside Queensland, cool minima also covered the northern and western Northern Territory, and the far north of Western Australia.
* Anomaly is the difference from the long-term average
After the exceptional and unseasonal rains of June in much of tropical Australia, there was a reversion to seasonal dry conditions in the region. No rain fell in a vast area covering almost all of the Northern Territory, most of Queensland away from the east coast, the Kimberley and some parts of eastern Western Australia, South Australia north of Marree, and NSW north and west of Bourke. Whilst such conditions are not unusual at individual locations over most of the region, the lack of any significant rain events anywhere in this area marked a clear contrast with June.
The all-Australian mean rainfall was 47% below the 1961−90 normal, with the Northern Territory (99% below normal, 3rd lowest) and Queensland (92% below, 5th lowest) both especially dry. The only state with above-normal rainfall was Victoria (+2%). The two main areas of above-normal rainfall were the western part of Western Australia south of the tropics, and most of Victoria (except for the Wimmera, the far southwest and some mountain areas). Both of these are areas which are suffering from severe long-term drought. There were also some above-normal patches in the Adelaide Hills and the Upper Southeast of South Australia, and on the southern border of New South Wales. Only a few small areas reached the highest decile, mainly around Exmouth and Carnarvon in Western Australia, and Geelong in Victoria.
With very dry conditions extending beyond their normal seasonal zone, rainfall was in the lowest decile in much of eastern Queensland (east of a line from Townsville-Hughenden-Thargomindah), as well as in northern NSW north of a Coffs Harbour-Dubbo-Broken Hill line. Records were set at a few locations within this region. Murray-Darling Basin rainfall for the month was 53% below normal, although a positive sign is the presence of a near- to above-normal snow pack over the mountain areas of southeastern Australia, which is critical for spring inflows into the Murray. There were also a few patches of very much below normal rainfall in parts of SA and WA, particularly on the Nullarbor.