PySky is a short Python script that uses the Dark Sky API to display precipitation data. It displays this data in natural English language across multiple time periods:

NOW
Rain, 44° F

NEXT HOUR 
Rain for 45 min

FOLLOWING 3 HRS
Moderate rain

NEXT 24 HRS 
Moderate chance of rain

PySky also creates a plot image of the precipitation intensity for the next hour:

PySky uses the matplotlib library for plotting. If you'd rather not install it, run pysky_noplot.py instead, which doesn't include the plot routine and will only output the text descriptions.

Because of matplotlib's many dependencies, it can be a tricky to install on OS X. Use Chris Fonnesbeck's Scipy Superpack if you want to avoid the headache. The script makes installing matplotlib really easy—just make sure you already have Xcode 4.5 and the associated command line tools installed.

In order to retrieve any data from Dark Sky, you first need an API key. You can register as a developer for free and get one. Then just create a .darksky file in your home directory (~/.darksky) and add this line, replacing 123456789abcdefg with your 32 character key:

APIkey: 123456789abcdefg

Change line 80

plt.savefig('/Volumes/MacHD/Projects/darksky-scripts/ds-rain-1.png', dpi=220, \

to a local path where you'd to save the plot image.

Run PySky with the following command:

python pysky.py {{Latitude}} {{Longitude}}

Where {{Latitude}} and {{Longitude}} are the desired Latitude and Longitude coordinates (in decimal form) of your location. If either or both are missing, a default location of the Apple Store in Cincinnati, OH is used.

This tool is handy for converting your address to coordinates.

GeekTool is my favorite way to use PySky. It allows you to have Dark Sky right on your desktop, just like this:

Download GeekTool from the App Store, install it, then drag two "Geeklets" onto your desktop—one "Shell" and one "Image".

Click on the Shell Geeklet and enter the Python run command in the "command" field. For example:

/usr/local/bin/python /Volumes/MacHD/Projects/darksky-scripts/pysky.py {{Latitude}} {{Longitude}}

Note: If you installed matplotlib into your default Python interpreter make sure to use usr/local/bin/python instead of just python, or else the module won't load. GeekTool doesn't create a shell environment exactly like you see when running terminal. Specifically, it doesn’t load any of the .profile, .bash_rc, or .bash_profile startup files.

Next, choose the Image Geeklet, and set the URL: field to file://localhost + the plot image local path. Like this:

file://localhost/Volumes/MacHD/Projects/darksky-scripts/ds-rain-1.png

Set the refresh time for both the image and shell script to whatever you like. Just don't make it <20 seconds or so—you'll hit the daily 10,000 API call limit. I personally have both refresh every two minutes.