Headed for cooler weather, climatologically

A lot of us have noted how humid this summer has been so far, accompanied by temperatures that have been on the hot side, though not in a record-setting sense.

We've been checking a few statistics, and through the first week and a half or so of August, this summer's high temperatures have been the 11th warmest out of 130 years of records for Raleigh, although due to some ties, 15 summers have been warmer.

Morning temperatures have been even closer to the top of the list, with morning lows this summer the fifth warmest on record, with only four summers having warmer early morning temperatures.

Part of the reason it has seemed especially steamy (and also contributing to the lack of cooling overnight) is that humidity has been especially high. The average dew point value for this summer has been 68.7 degrees, and that's tied for fourth most humid in records going back 73 years.

The good news, of course, is that climatology tells us we're past the peak of summer now, and temperatures will increasingly, if unsteadily at times, be on the decline over the next few months. I thought it might be interesting to plot a curve, shown above, that shows the change in normal high temperature between the first day and last day of each month through the year.

As you can see on there, the month of July is characterized by pretty steady temperatures, as we reach our peak for the year (on average), and the difference between the normal high on July 1 and 31 is only a tenth of a degree.

This month (August) is one in which the daylight hours continue to grow slowly shorter and the sun's maximum angle in the sky gradually decreases, but stored heat and a continued significant amount of incoming solar radiation leaves us with only a 3-degree drop in normal highs from start to finish.

However, as we head through the fall, a more rapid decline in day length and solar elevation, along with increasing passages of transient weather systems and cold fronts, brings a corresponding rapid decrease in temperatures, with November being the month that has the greatest average decrease in maximum temperature from start to finish.

Of course, beyond that, we pass the winter solstice in December, reverse the process, and eventually reach a peak increase in temperature for one calendar month in March, followed by continued warming into early summer.