Those of us who wait all winter for those lazy, hazy, hot days of summer have been disappointed this summer as the typical periods of hot, humid weather we normally see across a large portion of the central and eastern U.S. have been hard to find. Absent has been the subtropical ridge which we rely on to allow heat to build under the upper level dome of warm air.
Numerous recording sites from the Plains through the Midwest and into the East all are reporting very low numbers of 90-degree afternoon high temperatures so far this summer. In some cases the 90-degree mark has not been reached and time is starting to run out as summer fades into meteorological fall in just a week.
Hot weather has made an appearance across many portions of the central and southern Midwest and Plains during recent days but for many areas this is the first such "hot spell" of the summer and is not really anything to write home about. This burst of summer temperatures does not look like it will have staying power as some polar air gets back into the mix later this week across the northern half of the central and eastern U.S.
The reasons behind the cool summer are pretty much the same as the reason we saw the cold winter and spring. High latitude blocking has been a persistent feature across North America and through the Greenland region through most of the summer. Only during the past 5 days have we seen this blocking relax enough to allow the subtropical ridge to grow northward into the south-central U.S.
The Bermuda high has also been on vacation this summer and has tended to stay across the central Atlantic rather than poking west into the East Coast of the U.S. as it does many times during a normal summer. The lack of this "heat pump" has kept places like Boston, New York, and Washington D.C. with very few 90-degree afternoons.
More often than not we have seen polar air masses make their way southward into the Midwest and East bringing cooler, drier air. Some of these fronts have even made their way all the way into the southern U.S. bringing cooling to even our most southern states.
The Southwest has also seen "cool" weather during the past month with temperatures averaging as much as 2 to 4 degrees below normal so far during August. Phoenix, Arizona has seen 9 days during August when temperatures have failed to reach the century mark. Normal high temperatures are a few degrees over the 100-degree mark.
Current model products are telling us that summer may try to make a modest attempt to continue into early September with the mostly missing subtropical ridge expected to be more of a player in our weather across the central and eastern U.S. This might mean a few places may add a few more hot days into the tally before summer finally does fade away.
Doug Webster can be reached at firstname.lastname@example.org
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