Ichiban,
If the aircraft was in fact climbing the LOWER airspeed would make sense to some extent. It's also possible the pilot reduced speed due to expected turbulence in CB. Finally if you have reduced IAS and you are climbing you would have a reduced margin above the stall in clean configuration. This can be a trap in extreme turbulence where IAS fluctuates wildly.
Now I am not speculating at all just answering Ichiban,s question about the reduced speed.
Groggy