Welcome to summer.
At 10:42 p.m. on June 20, the earth’s tilt toward the Sun will reach its maximum point in the Northern Hemisphere, with the sun passing directly over the Tropic of Cancer. What we collectively refer to as “the first day of summer” (or the summer solstice) is also the beginning of “astronomical summer” — the roughly 90-day period during which the sun’s direct rays migrate southward from the Tropic of Cancer to the Equator.
In the world of meteorology and climatology, though, the seasons don’t quite align with the celestial calendar. They are instead grouped by temperature and mirror the civilian calendar. For example, December, January, and February, the coldest months of the year, are classified as “meteorological winter” in the Northern Hemisphere. Summer is defined as the months of June, July, and August. Simple. It’s also easier for narrative record keeping.
Except — not always. Here on the Outer Cape, our changeable weather and unique climate often render these seasonal definitions moot. Since spring can be a slog, our warmest average three months — our meteorological summer — are July, August, and September, the latter besting June by a few tenths of a degree.
This month has been a classic example. While we’ve had a couple of very nice warm summer days, we’ve dealt with a blocky weather pattern conducive to onshore wind and persistent cloud cover (not to mention some bummer weekend weather). It’s difficult to warm the air when the ocean is 55° F and the wind is blowing in from Nova Scotia.
But change is coming.
Forecast models show signs of a shift in the jet stream pattern. Upper-level ridging looks to build eastward into the Great Lakes and Northeast later this weekend and into next week, shutting off the supply of cooler air and potentially sending some midsummer-like warmth into the region. In fact, as of this writing, the European Ensemble Prediction System (EPS) — the premier long-range forecasting tool available — shows some 90° F+ temperatures in our neck of the woods next week.
An interesting side note: the EPS is unable to resolve the Outer Cape’s thin spit of land. While the model predicts an over 50-percent chance of 90° F+ temperatures in Hyannis next week, it shows a 0-percent chance in Provincetown and only a 4-percent chance of 80° F+ temperatures here. This is a nice example of where the art of meteorology comes in: if temperatures were to climb to the 90s in Hyannis, it would likely reach at least the 80s here on the Outer Cape as well.
We are nearing the end of the weather pattern that has supported cool temperatures and stubborn overcast. If all goes according to plan, this year the summer solstice may be the meteorological turning point, with the last week of the month turning decidedly warmer and more summer-like. While the sunsets are reaching their latest this week — around 8:20 p.m. — and the days will start getting shorter in the weeks ahead, summer is just getting started. No doubt the Cape’s best weather of the year is still to come.
