Re: Could there be a planet without weather patterns?

Great question!

The answer depends on what you mean by "weather patterns." Any orbiting body 
with an atmosphere will have, at least, wind. Because the atmosphere acts as 
a fluid, it does not rotate at the same speed as the planetary body itself,  
and wind belts will be present. Because these winds blow in opposite 
directions from belt to belt, small scale disturbances can occur at the 
shear zones where the belts contact one another. A good example of such a 
disturbance is Jupiter's Great Red Spot, which is located on a shear zone. 
(Its size and longevity are affected by other factors, which I'll mention 
shortly.) Uranus and Neptune, though their atmospheres too are modified by 
other factors, are good examples of planets where the primary source of 
activity in the atmosphere is a consequence of global rotation.

Weather on Earth is the result of three factors acting in combination: 
global rotation, variations in temperature, and moisture. The Earth receives 
an immense amount of heat from the sun, and acts as a giant heat engine, 
moving cold air from the polar regions southward and warm air from the 
tropics northward. As the warm air rises and the cool air descends, Coriolis 
forces cause the air masses to rotate. Warm air masses (lows) are light; 
cool air masses (highs) are dense, and winds form between highs and lows as 
Nature acts to balance the pressure between them. Moisture plays a big 
factor: if warm moist air is lifted, the vapor condenses as water droplets, 
which result in rain or snow, and if a sufficiently moist package of air is 
lifted quickly enough, severe weather can result. The gas giants also have 
weather, but the primary source of heat on these planets is from the 
internal heat reserves of the planet. The effects, however, are the same, 
which is why all four of these planets, to greater or lesser degrees, show 
distinct atmospheric disturbances.

What of a small planet with no internal or external heat source and no 
atmospheric moisture? In such a case, weather would be restricted to wind. 
With no moisture, precipitation would not occur. With no heating of the 
atmosphere, there would be no rising or falling of air or areas of pressure 
differential. It would just be windy all the time.

I hope this short answer to a complex question is clear.