A water logged radome is bad news. The water will freeze at high altitudes and you will be lucky to pick up a Cb at 20 miles. That is because a thin coating of ice absorbs the radar beam and very little energy goes beyond the radome. We had this trouble on a B737-200 during operations over the Central Pacific region. For example, we could normally pick up a large island like Guam (60 miles long)on the 180 mile range - but it would only show up at 80 miles. Big Cb would not show until you were on top of them. No fault found by the techs. The ice had melted by then.
I took photos of the radar screen and of Cb and sent them to Bendix. Bendix said check the radome for moisture. The techs then found pin hole damage in the radome. They baked the radome in a special oven - which dries out water - and repaired the holes. No further problems.