Suppress values from multiband rasters

I have a raster stack with 84 bands . It is a time series raster. It so appears that the cloud is causing error in my processing and hence i need to suppress or replace them by a NaN to eliminate them from processing. But Since clouds are not static so there is variation in cloud in all the bands making it impossible to mask the clouds using default envi option (I have ENVI+IDL 4.4). Is there a possible way with which i can mask each band of its raster stack based on the value less than a certain value.