Climate of Mount Isa

Three main seasons are experienced in Mount Isa 

Mild temperatures with low humidity (MAY to AUGUST) 
Hot temperatures with low humidity (SEPTEMBER to DECEMBER) 
Hot temperatures with high humidity (JANUARY to APRIL) 

  
Although maximum temperatures can reach well into the 40-degree scale in Summer (45.9 degrees on the 29th of January 1990 the highest temperature recorded for Mount Isa), the higher elevation of the Northwest uplands from the surrounding area (150m higher) has a significant moderating effect on temperatures. This can be shown by the temperature differences experienced in Mount Isa as compared to neighboring townships such as Cloncurry, Boulia, Winton and Urandangie on the Western Plains. 

Night time temperatures in Mount Isa can often be much cooler than those of nearby centres. Mount Isa is located in a valley between two spurs of the Selwyn ranges. On clear nights, the moderate southeasterly winds experienced on the Western Plains and Barkly Tablelands keep the temperature higher. The calm conditions experienced in Mount Isa due to the sheltering effect of the ranges leads to lower temperatures being recorded (this can be up to ten degrees lower in extreme cases). 

Due to the continental climate of Mount Isa, the diurnal (daily) temperature range is approximately 10 to 15 degrees throughout the year, although can be as high as 20 to 25 degrees at times. Except for the months of June, July and August, temperatures for the area are described as warm to hot. However, very low minimum temperatures can occur (lowest ever minus 2.9 degrees on the 7th of July 1984) due to the often clear skies experienced in the winter months. Negative temperatures have occurred during the months of June, July and August. Although Mount Isa is just south of the limits of frosts, the area rarely experiences frost conditions to the same degree as continental areas further south. 

 
Variability of rainfall in the Mount Isa district is in the order of 20 - 25%. This is verified by annual rainfall amounts that may be less than 250mm in one year and greater than 500mm the following (161mm in 1970 being the lowest yearly rainfall recorded, and 864mm in 1974 the highest). A district wet season usually occurs from December to March, with over 75% of the annual rainfall occurring during these months. 

A failure of the wet season causes severe strain on the pastures and available surface water supplies. The onset of drought is greatly enhanced by the high evaporation rates during the summer months, although the loss during the dry season is less due to the lower temperatures. 
  
The districts rainfall usually comes from thunderstorms that form due to the intense heating experienced during the summer months, and from the passage of the inland trough system prevalent during the  Spring and summer months. 

Occasionally, quite heavy and prolonged rain can occur with the passage of ex tropical cyclones, which can lead to an extension south of the monsoon trough from the northern areas of Australia. With it can come flooding of local river and stream systems, with its associated dislocation of local infrastructure.