Overnight temperatures were between four and eight degrees above average for much of southwest Western Australia overnight Friday and into Saturday morning.  

In the Central West district, Geraldton Airport cooled to just 20.6 degrees, which is 8.6 above average. North Island (off the Central West coast) had their warmest May night in the 20 years of records, dropping to just 23.4 degrees. 

Further south to the Lower West, Gingin Airport and Dwellingup were 7.5 and 6 degrees above average respectively. In the Southwest the biggest deviation from average was at Collie East where the overnight low was 14.5 degrees, 8.6 above average.  

It was a similar story around Perth with most suburbs between five and seven degrees above average. The city itself cooled to 16.9 degrees, which is 6.5 above average. Although it was warmer earlier this month, you need to go back to 1999 to find a higher overnight temperature this deep into May. 

These above average temperatures were made possible by a mild airmass lingering over the southwest of the state, coupled with extensive overnight cloud. This cloud cover served to trap much of the daytime warmth, bringing the mild overnight temperatures. 

Image: Cloud over southwest WA on Saturday morning. Source: Himawari-8 Satellite

The next few nights and mornings are expected to be equally as mild and even a degree or two warmer early next week. Skies to begin to clear from mid-week, bringing cooler nights and mornings.