What's the duration of seasons in Reign of Giants DLC?

I'm playing it now and the summer abruptly ended by turning into winter on about 27th day. But now that it's day 37, it's raining, which looks kinda like spring, but when the rain stops, it becomes freezing cold again.

What seasons last for how long and what are the environmental effects to be aware of (such as rain, frog hail, megaheat)?

• Winter lasts for 16 days. Beware freezing.
• Summer lasts for 20 days. Beware overheating.
• Spring lasts for 20 days. Beware rain: this means freezing, lightning, and/or frogs.
• Autumn lasts for 20 days. This is the calmest season. There is light rain.

The times listed are the default Sandbox modes, though Adventure Mode or your personalized settings may have differences. Of course, one should beware the different seasonal monsters, too....