Having a clear-weather friend sounds like a good idea. They tend to be supportive during the best of times and are always willing to offer help without being asked. Being around them makes the heart warmer a accept one for being themselves. That is, until problems boil to the surface and criticisms involving them begin.
In most friendships there may be rough patches that creates conflicts. Clear-weather friends are absent when clouds appear; for bad weather makes them feel uncomfortable and they think they are under assault. They cannot be criticized in the slightest because they are flawless in their mind. This is to the point anything directed at them is reflected toward the sender. Similar to what you say bounces off of me and sticks to you.
Deep down inside clear-weather friends are manipulative, but do not realize it. They try to always tip the scales in their favor by distorting reality to benefit their goals. Their sense of entitlement makes them feel principled and strong and beyond reproach. Whenever things go wrong in a relationship it cannot be their fault. Their blind spot keeps them in the dark and stuck in the same position in life.
They are available in the best of times, but not the worst. The relationship is nonreciprocal and possibly detrimental to the sanity of those around them. Friends are essential no matter what the weatherman says the future models show. Considering how flakey clear-weather friends can be, most of the time it would be better to brave the elements alone.