There are contradictory answers to this question: Yes you can, and no you shouldn’t.
You can, if you obey a few basic rules. Firstly, your equipment must be certified as being safe to use in wet weather. If it is, you are able to safely proceed with your planned house washing project. However it is recommended that you store your equipment under cover, don’t leave it outside where it is likely to be exposed to the weather for a long time.
Cleaning on days when there is cloud or light rain might really be easier. If the surfaces are already wet, your pressured water jet has less trouble dislodging the dirt and grime. If you are using detergents, they will have more time to do what they are supposed to do. Rainy weather will aid in rinsing the detergent away, and will also benefit your plants or grass by washing off any detergent drips.
Another advantage for power washing when it’s cloudy or raining, is that the sun has basically been “dumbed down”. You won’t have the problem of looking up into a bright sunny sky, and the glare of sun on water makes it hard to see what you are doing.
So, if your equipment is certified safe, and the rain is light, there is no reason to prevent you from getting on with the job. Just make sure you are safe, and reconsider whether you must use a ladder or other platform to reach up high. These can become dangerous in the rain, as their surfaces will become slippery.
This is the “yes” argument for basic, standard, light rain. But rain doesn’t always behave in a sedate manner. If there is very heavy rain, strong wind or storms, by no means should you consider going out there with your pressure washer, even if it is safety certified.
If you don’t have experience with pressure washing, you run the risk of accident through slipping on wet surfaces, so don’t take chances in heavy weather. Gain the necessary experience by starting out in fine weather, perhaps early morning or late afternoon, until you are confident in being able to handle the equipment in wet weather. But even when sufficiently experienced, do not go out in a storm. It should not be necessary for me to say that, but I want to make sure that particular piece of information is emphasised.
There may be a reason why your power washing project must proceed regardless of the weather. Maybe you are planning to sell your home or commercial property, and want it to look its best. My recommendation is that you get in touch with a company which is well experienced in pressure cleaning in Townsville, and then you can be confident in the knowledge that the job will be done well, and more importantly safely, by someone who is familiar with this work.