The endless summer — 2011. It’s been a wild ride with earthquakes, floods, wildfires, drought and heat. It may be that despite all the weather features that grabbed the headlines this past summer, it will be the heat that is remembered for generations to come. And the drought. (Not to mention the dreadful spring season that saw the earthquake and tsunami in Japan and the brutal tornado outbreaks across the Southeast and in Joplin, MO.) Then again, I’m writing with a southern perspective and more specifically a Houston base. I’m sure the folks in Vermont would like to take on just a little bit of our drought if they could pass along some of their flooding issues to Texas.
But the summer is drawing to an end, and I have to look no further than my desktop calendar which says autumn begins a week from today as the autumnal equinox rolls into town. As with the climatological peak of hurricane season (September 10), we can see the end of the season but it’s not quite over — there’s still more heat and a whole heck of a lot of drought to come! However, the seasons are unstoppable and as early as even a few weeks ago, the telltale signs of winter have been evident in the northern latitudes and the upper atmosphere.
One of the surest signs of the approaching winter season is a lowering of the tropospheric heights in the Northern Hemisphere. The cold, dense air of winter occupies less space than the warm, uncompressed air of summer so that during the peak of summer, with the Northern Hemisphere tilted toward the sun, the troposphere warms and expands. A constant pressure that was, for example, at 20,000 feet finds itself much higher in the warmer, more lofty air. The reverse is true, as well: what goes up must come down and as the Northern Hemisphere begins to tilt away from the sun in advance of winter, the troposphere begins to cool and contract. Those same constant pressure heights begin to sink. Tracking those heights is a sure way to watch the seasons change.
Even in Houston, we saw our first cold front last week. Late August temperatures well above 100F were replaced by more seasonal temps in the lower 90s. What a pleasant, pleasant change. And another cold front had just enough strength to slip past downtown Houston yesterday afternoon. That’s likely the death knell for the triple digit heat wave that has plagued so much of the central U.S. for these past many months. And, what’s this? Rain? It’s true. As the oppressive high pressure that has been seemingly anchored over Texas finally begins to weaken, it allows stagnant patterns to shift and cold fronts to slip farther south. It’s just a matter of time before the Gulf Coast is up in arms and shutting down school districts due to the threat of freezing temperatures. I for one can’t wait.