World and Nation

Sunny September to Continue

Sunny September to Continue

When people ask “When’s the best time to visit Boston?” I smile and think to myself, “could they have asked an easier question?” September is certainly the best time. Climatologically, this is the month with the most number of sunny days. Combine that with the comfortable temperatures, this is the month where anybody would be able to enjoy the outdoors (OK, maybe not those pesky skiers). Excluding the effects of the two tropical storms, this September is no different. In fact, if you blindly believe the numerical weather prediction models, there will not be any rain for the next two weeks!

Why is September so unique? In the summer, the radiational heating is so much stronger, and as a result, the surface becomes too warm and the air turns convectively unstable, likely generating thunderstorms. In the winter, the solar heating differential from equator to pole is much greater. As a result, there is a large temperature difference, providing “fuel” for storms to develop. (Boston also gets the “bonus” feature of being by the ocean where the (colder) land and (warmer) ocean contrasts are even greater.) Finally in the spring, because the ocean is colder than the land, the sea breeze “kicks in” and usually provides cloudy skies in Boston. However, as exhibited so far (and will be shown) this month, in the absence of all these processes, a sunny September will prevail.

Extended Forecast

Tonight: Mostly clear. Lows near 50 F (10 C).

Tomorrow: Sunny. Highs in the mid 70s°F (24 C).

Tomorrow night: Mostly clear. Low in the mid 50s°F (12 C).

Thursday: Sunny again. Highs in the mid 60s°F (18 C).

Friday: Sunny still. Highs in the lower 60s°F (16 C).