True, it did not yet seem possible here Tuesday to say we had shut the door on summer.
But perhaps it was not too hard to see that we are about to do so. No, Tuesday with its high of 86 degrees did not yet provide the invigorating stimulation of autumn. Yet the summer-
weary could note approvingly that even at 86, Washington’s high came in at two degrees cooler than the day before.
Two days of readings scarcely constitute a trend. But it did seem like a small step in the desired direction, if that direction is toward the cool and the crisp.
Hints of an advance on Tuesday toward the electric vitality of autumn may also have emerged from other atmospheric parameters.
For example, Tuesday seemed less humid than Monday, and the figures backed it up. If we felt just a trifle jauntier on Tuesday, we might not have considered citing its dew points. But the day’s lower dew points, reflecting a decline in spirit-sapping humidity, might nevertheless have been a plausible explanation.
Also, at summer’s end, no matter how warm the days, signs of change appear that are immune to the vagaries and capriciousness of temperature and humidity.
Among those, of course, is the loss of daylight. At this time of year, it amounts to about 2½ minutes each day.
However we may delight in the mid-or-upper 80 degree temperatures of Washington’s late summer , geometry and astronomy afford us less and less daylight to enjoy them
Earth is about to rendezvous Thursday with one of the two spots on its orbit where our hemisphere tilts neither toward the sun, nor away.
From then on we begin a long period of tilting away. It is inexorable. It means a comparative lack of sunlight and warmth, and perhaps underscores the bittersweet nature of astronomical autumn: a time of both brilliant color and growing darkness.
Further signs of impending fall may be found by recourse to the record book. Monday’s 88 degrees was eight degrees above the average high temperature for Sept. 19. Tuesday’s 86 was seven degrees above the average high for Sept. 20.
Not to make this an exercise in algebra, the explanation is that as the daily high temperatures decline, the average high temperatures are also in decline.
The average high for Monday’s date was 80. But the average high for Tuesday was 79.
Tuesday was the end of a long period in which our daily average highs were 80 degrees or above. We now embark on a long period in which the daily average highs will remain below 80. It is a small step on the path toward autumn and cooler weather. But it is a significant one.