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Posted at 10:30 AM ET, 07/ 6/2009

June Recap: Another Wet Month

By Don Lipman

* Nice Start to Week: Full Forecast *

Rainfall (in inches) during the April-June period the last two years compared to average at Reagan National Airport (DCA).

Although not as extreme as May, June 2009 continued the trend of wetter than average weather in the D.C. area. After almost 6 inches of rain last month, the rain gauge at Reagan National Airport (DCA) has now collected 18.13 inches for the period April 1st through June 30th, almost double the 9.72 inch normal amount-- but still less than the 20.38 inches for the same period last year. As in May, last month's weather was punctuated by several severe thunderstorm episodes resulting in property damage, personal injury, and in some cases, death. Significantly, there were five days during which .50 inches or more of rain fell.

Aside from the heavy rainfall, it was a fairly typical month temperature-wise, with no unusual heat or cold. As heat was building throughout the Plains and the Midwest, a persistent dip in the jet stream kept the Northeast and Mid-Atlantic states relatively cool, except for a few brief periods. As a whole, the month averaged just a little below normal, similar to May in that respect. Nonetheless, we had the fewest number of 90 degree days in 17 years (just 2) and, when combining May (0) and June, the fewest number in 24 years.

Why has it been so wet and relatively cool (for Washington) you ask?

Keep reading for possible explanations for June's weather...

Temperatures during June at DCA compared to records.

The aforementioned dip in the jet stream is the immediate answer, of course. And why, has the jet stream meandered so far south of its usual Canadian haunts for much of the spring and summer? It's tempting to blame various "teleconnections," or inter-relationships, between large scale atmospheric pressure patterns in different parts of the world. Some of these are the NAO (North Atlantic Oscillation), the PDO (Pacific Decadal Oscillation), and the more well known ENSO (El NiƱo Southern Oscillation), etc.

Also, it would be easy to blame large-scale volcanic activity, if there were any, or lack of sunspots, which astronomers have reported. (The U.S. had a relatively cool summer after the 1980 Mt. St. Helens eruption and a "spotless" sun has long been associated with the famous, or infamous, "year without a summer" of 1816--see my last post.) But that wouldn't explain the excessive heat that's already occurred in the Midwest. The notorious heat pump known as the Bermuda "high," currently in an anemic state, could also be implicated in our current weather.

But my gut feeling is that currently the weather around these parts is just in a "rut" (meteorological term). Weather patterns are very cyclic in nature and these cycles, once established, tend to last for days, weeks, or even months. And while I'm certainly not predicting a "year without a summer," pleasant Washington summers are not as rare as you might think; at least they weren't a few generations ago. I, for one, would welcome one, even though, for sure, there would be the usual grumblers.

By Don Lipman  | July 6, 2009; 10:30 AM ET
Categories:  Lipman, Local Climate  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Another Cooler Than Average Week
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Please see my earlier post.

Volcanic activity includes Mt. Redoubt, etc. More recently a volcano in the Kuril Islands between Kamchatka and Hokkaido erupted with quite a bit of ash. The sunspot minimum also factors in. Subtropical ridges are a bit south of their usual summer positions this year; this is heating up the weather in the Arklatex region.

We could get our hot weather later this month and August. Will need to check the ENSO report.

Posted by: Bombo47jea | July 6, 2009 12:21 PM | Report abuse

Why do you emphasize sunspots in connection with the summer of 1816? Stommel's definitive analysis "Volcano Weather" provides strong evidence of the effect of the Tambora eruption, which was the biggest known in at least 1600 years. This conclusion has been subsequently supported by the modeling of Robock and others.

Posted by: CapitalClimate | July 6, 2009 12:27 PM | Report abuse

How did you get "four days during which .50 inches or more of rain fell"?
From NWS (WS FORM: F-6):

Date   Amount
3 1.50
4 0.52
5 0.57
9 0.89
18 1.01
The 2 days over 1" were 2.5 times normal.

Posted by: CapitalClimate | July 6, 2009 1:42 PM | Report abuse


In Don's last post on "the year without a summer" which is linked to above, Don cites the volcano as the primary cause. But it is also well-established that sunspot activity was low during that period, hence the reference.

The four days of at least .5" was a typo and fixed.

Posted by: Jason-CapitalWeatherGang | July 6, 2009 3:22 PM | Report abuse

What intrigues me is a possible correlation between sunspot minima and significant volcanic events as discussed in this 2003 research paper: -This would explain the debate regarding whether volcanic or solar activity was the biggest contributor to the Little Ice Age.

Posted by: MattRogers | July 6, 2009 4:00 PM | Report abuse

Regardless of the possibilities, this summer has been rather pleasant to this point. One can only hope that the 90-100 degree days with high humidity continue to be kept "at bay".

Posted by: bodyiq | July 6, 2009 5:06 PM | Report abuse

"During the decade 1811 to 1821 sunspot activity was unusually low, but during 1816 it was higher than any of the other years of the decade."
Stommel, p. 153

Posted by: CapitalClimate | July 6, 2009 5:58 PM | Report abuse

Ref: CapitalClimate | July 6, 2009 12:27 PM. Don at Capital Weather Gang: I didn't emphasize, or even mention for that matter, sunspot activity as the cause of the "year without a summer," although it may have contributed.

Posted by: Weatherguy | July 6, 2009 6:05 PM | Report abuse

How is this statement referring to volcanoes and not sunspots?

". . . a "spotless" sun has long been associated with the famous, or infamous, "year without a summer" of 1816"

Posted by: CapitalClimate | July 6, 2009 6:22 PM | Report abuse

Clarification to CapitalClimate | July 6, 2009 12:27 PM: fm Don at CWG. As noted in my previous post, I did not mention (lack of)sunspot activity as a factor in the article on the "year without a summer." However, in my recent article on June weather, which linked to the first article, I did refer to, but discounted, sparse sunspot activity as a hypothetical factor in our current cooler than normal weather. It would have been more appropriate, however, to say that a "spotless" sun has long been associated with the "Little Ice Age," the roughtly 500 year period ending around 1850, rather than the single 1816 event.

Posted by: Weatherguy | July 6, 2009 6:31 PM | Report abuse

Keep in mind that the very wet period April through June LAST year was followed by a dry summer (less than "normal" rainfall) throughout the Metro area. While September was wet, October 2008 was one of the driest Octobers on record, and the dry spell continued to April this year. Indeed, April 2009 was the first month since Sept. 2008 with normal or above normal precipitation around here.

Moral: The recent past (persistence) is not a great forecast tool of what will come over the balance of the summer and beyond.

Posted by: SteveT-CapitalWeatherGang | July 6, 2009 7:41 PM | Report abuse

SteveT, while July and December '08 were technically dry, it was by the narrowest of margins. Thanks mainly to May's excess, the year overall was 18% above average.

Posted by: CapitalClimate | July 7, 2009 2:42 PM | Report abuse

Thanks CapitalClimate, alias nitpicker??

More importantly my real point was that the rainfall deficit from last fall did not begin to end until April and not eliminated until June. See:
cumulative precip at DCA

Posted by: SteveT-CapitalWeatherGang | July 7, 2009 4:20 PM | Report abuse

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