At 9:24pm Pacific Daylight Time tonight, the Sun will reach its northernmost point of the ecliptic – the crest of the “seasonal sine wave.” Beginning tomorrow, and continuing through December, the amount of solar energy entering earth’s Northern Hemisphere will begin to decrease. The change will be almost negligible for the next few weeks, but by August we’ll be able to notice the darkness of night encroaching on our world once more.

Depending on your definition of the seasons, it’s either the beginning of summertime or the midpoint – or neither! Here are the three definitions:

It is the midpoint of Solar Summer, which runs from May 5 through August 6 in the Northern Hemisphere. Solar Seasons are based exclusively on strong vs. weak sun angle, and late June is when the sun is strongest.

The summer solstice is the beginning of Astronomical Summer. This is the seasonal calendar most of us grew up knowing as “official.” Astronomical Summer begins on June 20/21 and ends around September 22, the fall equinox. In climates with quite a bit of summer “seasonal lag,” such as Western Oregon, this definition actually works out pretty well. Average temperatures tend to peak in early August, and September is slightly warmer than June most years.

However, weather and climate buffs tend to use Meteorological Summer for their analysis of seasonal weather. Meteorological Summer begins June 1 and ends August 31. In MOST of the North American continent, these are the three warmest months of the year – and beginning the seasons on the 1st of the month makes statistical analysis much easier. (The fact that meteorological summer begins right after Memorial Day and ends immediately before Labor Day, is also congruous with popular culture.)

None of these three definitions is a perfect fit for every climate region. Here in The Dalles, our average temps tend to peak in the last week of July, historically speaking. Usually we notice the nights start to cool down in the 2nd half of August, as the nights get longer and ‘pre-fall’ airmasses begin to develop over Canada.

Speaking of pre-fall? We have an interesting pattern on tap for next weekend. Normally our early summer heatwaves are pretty short-lived, and hotter in the Columbia Basin than in Portland or the Willamette Valley. That was the case during Sunday-Monday’s brief hot spell. We hit 96 in The Dalles, and widespread mid/upper 90s eastside even in the high desert. But only upper 80s in Portland and Eugene.

Today the westerly breeze has returned and we will be closer to our normal seasonal temperatures (about 80 degrees). As we get toward Friday and Saturday, a relatively cool upper-level trough forms over the Upper Midwest and Great Lakes. Surface high pressure over Western Canada slides southward, just east of the Rocky Mountain Crest. That will mean somewhat cooler air over the Northern Rockies and Northern Plains. Also on Saturday-Sunday, a hot thermal trough from California begins to come up the Oregon Coast. It’s the perfect setup for very hot temps 95-100 in the valleys of Western Oregon, but not a prime heatmaker for the east side.

It’s pretty unusual to have a hot pattern in June, where the west side is actually hotter than the east! But that could well be the case both Saturday and Sunday, especially if ample offshore flow develops. This is more like what we typically get in early September, as the weakening sun over the Canadian interior allows cooler and stronger high pressures to form. Except that now a similar pattern is trying to develop when the sun is at its strongest….

What will my inner weather geek be focused on this weekend? Obviously the temps in Western Oregon bear watching, especially down near Brookings on the south coast. But the modified Canadian airmass will also have an effect on weather in Eastern Oregon and Washington. Normally when we lose the west wind through the Gorge at this time of year, temps very quickly skyrocket. That might not be the case this weekend; if anything the low dewpoints could result in COOLER temps Friday and Saturday night!

In any case, it will be fun to analyze an “End of Summer Style” pattern occurring in early- to mid-summer instead. What effects, if any, will the shorter nights and stronger sun have on the distribution of wind and temps (both day and night)???