SOME parts of NSW just had both their coldest and warmest July in more than two decades, when considering maximum and minimum temperatures separately.
This may seem odd, however warm days and cold nights are actually a typical sign of drought.
Most of NSW received less than 20 per cent of the usual July rainfall and some places registering their driest July on record.
For example, the 0.8 millimetres of rain recorded at Forbes last month was its lowest July total in more than 140 years of records.
Broken Hill’s paltry 0.4mm during July followed its driest first half of a year on record, with data available back to the late 1800s.
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During drought, reduced moisture on the ground and in the top layers of soil cause the air immediately above the ground to become drier than usual.
This has a significant effect on overnight temperatures, because drier air can cool down further than more moisture-laden air.
Put simply, drier air can reach lower temperatures before condensation occurs, at which point some energy is released back into the air and the rate of cooling slows.
The drier the air, the lower the dew point, and the more the air can cool down before condensation kicks in. This cold-night effect is enhanced even further during drought by a lack of cloud cover.
Clear skies at night allow the previous day’s heat to radiate into space, while clouds help trap some of this warmth in like a blanket.
In contrast to cool nights, clear daytime skies during a drought typically cause maximum temperatures to be above average, thanks to abundant solar heating.
As a result of the drought, Parkes just registered its lowest mean minimum and highest mean maximum temperature for July in 20 years of records.
