The mountains can and will block airflow from higher pressure systems that come in from a coast and won't combine to nake storms
Explanation:
Given
Refractive Index 
angle of incident
Light originates in the medium of higher refractive index
Let 
and 
be the incident and refraction angles respectively thus according to snell's law
(b)Ray originates from lighter medium
Well, that's not actually "diffraction".
The fuzzy edge of the moon, and the added glow that's sometimes seen
around it, are all effects caused by the light passing through air before it
reaches you.
This gives you some idea of why astronomers go to such effort and
expense to get their telescopes above as much of the atmosphere as
possible ... placing all serious observatories on mountaintops, and even
putting telescopes in orbit. It's all because the air does such a job on the
light that's trying to shine through it. We have to make do with whatever's
left over after that.
Answer:
Extrasolar planets are very dim light sources compared to their stars. At visible wavelengths, they generally have less than a millionth of the brightness of their parent star. It is extremely difficult to detect this type of dim light source, and in addition, the parent star has dazzling light that almost makes it impossible.
