Pack your layers when traveling to Boston, Mass. RELATED LINKS Return to Boston City Guide

Boston's weather can be affected by a wide range of factors, including (but not limited to) frigid arctic air descending from Canada, tropical storms blowing up from the Caribbean, blustery nor'easters swinging in off the north Atlantic, and stalled high-pressure systems that can bring blistering temperatures in summer.

Whenever you visit, prepare yourself for variable conditions, bearing in mind that rain can fall pretty much any time of year. The best strategy is to pack layers, so you can add or subtract articles of clothing to suit the conditions. Even in summer, a sweater or jacket can be essential, and a raincoat and/or umbrella might come in handy any time of year.

That said, spring and fall can bring particularly lovely weather to the New England coast, with predominantly mild conditions whenever the sun is shining. And even when the weather is lousy, Boston offers plenty of indoor attractions to keep you out of the elements.

If you're out on the town and have neglected to check the weather forecast, look for the spire of the Berkeley Building in Back Bay, also known as the "old John Hancock Building." This 26-story office tower has a beacon on top that shines blue when clear weather is expected, flashes blue for cloudy weather, glows red for rain and flashes red if snow is in the forecast. There's even a little poem to help you remember the code:

Steady blue, clear view
Flashing blue, clouds due
Steady red, rain ahead
Flashing red, snow instead.

Remember, however, that in summer, a flashing red light means that the upcoming Red Sox game has been canceled. And if the lights flash blue and red simultaneously, as happened for the first time October, 2004 it means the Red Sox won the World Series.