- How heavy is the rain?
- Is there significant wind?
- What surrounds your house?
How heavy is the rain?
If it's raining cats and dogs then it's possible for dirt located above your windows on the exterior of your house to wash off and onto your glass. This may leave a mess on the glass.
Is there significant wind?
Strong wind can whip up dirt and dust and deposit it on your windows and as the windows are wet it may stick to them.
What surrounds your house?
Tree leaves are great for holding dirt and dust. If trees are located close to your house, it's raining and there's strong wind then this could effect your windows in the rain too.
In Hobart and surrounding suburbs our rain is often drizzley and light and I find it rarely makes any difference to a great window clean. However, the reality is you know the conditions around your house better than anyone else so you're in the best position to make the call.
I can give you some peace of mind though: If your windows do get messed up by rain on the day I clean them or even the day after, let me know within that 48 hour period and I'll be happy to come back and touch up the outside again :)