This made me say "wow". Weather Spark [weatherspark.com] provides highly-detailed interactive weather graphs of the entire history of any weather station on earth.
Weather records can be grouped or filtered by way of an historical timeline (bottom right). Specific weather stations can be compared, such as those of New York versus San Fransisco (select with shift key to add other cities). Available graph attributes (don't forget to scroll down the interface if some are not visible) include sun, clouds, precipitation, temperature, dew point, temperature, humidity, pressure, wind direction and speed.
Specific locations and time ranges can be easily shared through a unique URL, such as when the severe windstorm called Gero passed through the Benbecula weather station on January 11, 2005 with wind speeds of more than 31m/s, or to illustrate the monsoon in Mumbai.
What other remarkable weather phenomena can you discover?