Sometimes it is good to go out to the inspection on a rainy day. The inspection lasts several hours so there's usually a long enough pause to get up on the roof safely. The benefit is you can find active leaks that would not show up during periods of no rain. Thermal imaging is great but you need moisture to be present to detect anything. So I don't normally cancel inspections on rainy days I take advantage of the opportunity to see how water tight the roof and structure area.
Today I found high moisture on the ceiling around the water heater flue pipe that may not have shown up during a dry period. After I scan an area with the thermal imaging camera I am able to use the moisture detector to verify high moisture.