Design a set of small weather icons

FoggyNoggin

Mac and iPhone Software

I need a set of weather icons for a desktop Mac app. The icons will be displayed in the menubar, so must be optimized for a small size.

I will be layering the icons to make the final image. For example a Sun image layered with a small amount of clouds would be "Party Cloudy."

I will also be layering the icons over various backgrounds, so they need to look good on all backgrounds.

Though I'm thinking of something a fairly realistic style, I'm not set on that, so the style is up to the designer. The size should be 30 pixels wide by 20 pixels tall.

Icons I need:

Background: day
Background: night
Background: dusk
Background: overcast

Sun
Moon
Small amount of clouds (to make partly cloudy)
Larger amount of clouds (to make mostly cloudy)
A lot of clouds (for cloudy or overcast)
Rain
Thunderstorm
Windy
Fog
Hail/Sleet
Snow
Snowstorm/Blizzard

Keep in mind that the weather icons will be layered on the four backgrounds. So the size of the weather icons is likely (but not required) to be smaller than 30 x 20 so they don't look cramped.

If possible, I'd like the deliverables to be in layered PSD or AI format.