Slow deep fading on 2m

As the PI7CIS beacon on 2m seems a good propagation indicator it was interesting to see what happened in the rain today around 1325z. Whereas the beacon seems to be nearly always copyable, but not moving the S-meter on the FT817, it was in a deep,slow fade around 5 minutes long just now  - still there, but maybe 6dB weaker. Looks like it is copyable most of the time but a bad fade would make it not readable.