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Posted at 11:00 AM ET, 04/ 9/2010

Normally, our weather is not so normal

By Don Lipman

* Welcome back, spring! Full Forecast | Pollen is blowin' in the wind *

Observed, normal and record temperatures for April 2010 at Reagan National Airport. While the recent heat wave was pretty extreme for April, in general it's fairly normal for our weather to be abnormal. Image credit: NWS.

A few weeks ago, some of you may remember my article, "Believe it or not, D.C.'s is a Climate to Relish," in which I argued that, despite our winter of record-setting snow, the D.C. area's climate -- the highs, the lows, the extremes and the normals -- is relatively tame compared to other parts of the country. As a postscript to that article, and in the wake of yet another period of notable weather (this time a stretch of summer heat in early April), I will now focus on the latter of those climate components -- the "normals."

We all know (especially the savvy readers of CWG), that it's a rare day or month when temperatures, precipitation, etc., are exactly "normal" as defined by the long-term averages. Therefore, we might say that "abnormal" weather is, in fact, really the norm, and vice versa. That being the case, do the media (CWG included) stress the "abnormality" of the weather too much?

Although abnormalities of the weather are anything but unusual (unless unusually protracted), my observation is that people don't want to hear that, especially after a long stretch of brutal cold or heat and humidity. Instead, we seem to delight in being told that if we had to suffer, at least we suffered more than anyone else ever did during that particular period.

Sensing our need for this "suffering quotient," the media are happy to oblige and advertise our discomfort level in the form of departures from normal, broken records, etc. And it doesn't matter that, from a climatology standpoint, official records go back a mere speck in time and that 200 years ago it might have been far hotter or far colder or far wetter.

Abnormal is abnormal.

U. S. weather normals, or averages, are based on only the most recent three full decades, although official records for most major cities go back nearly 140 years. The normals are readjusted after each decade by adding the latest and deleting the earliest 10 years of record from the 30-year base period. In this way, climatologists can detect climatic change more easily than if each additional year's records were averaged in with all preceding years. Current normals, then, are for the period 1971-2000, and will be readjusted after this year.

Realistically, even 30 years may be too much time upon which to base weather normals because many people tend to think of normal weather as very recent weather. After a very snowy winter, such as we just had, preparations (purchase of a new snowblower, HVAC system, etc.) are often made for more of the same, even though the odds of an immediate repeat performance are quite low. (Following the snowy winter of 1995-96, snowblowers along the upper East Coast were almost sold out by the end of the following summer. As some might remember, however, the next several winters saw little snow throughout the mid-Atlantic states.) What kind of preparations, if any, do you think people will make for next winter?

In using weather normals to compare current weather with the 30-year averages, meteorologists and climatologists give little thought to day-to-day "abnormalities" unless the departures are extreme and of great duration. They understand that these differences are just part of the big picture, part of what makes up the long-term averages.

I don't think even large departures from normal are likely to startle the National Weather Service, since experts know that the last 160 years have been an especially docile period in Earth's climatic history. It is well documented in folklore and in historical fact, for example, that a 400-500 year worldwide reign of severely cold winters and coolish summers ended as recently as 1850. This period, which coincided with the great age of exploration, was known as the "Little Ice Age" and was accompanied by glacial advance, fallen food production and, in general, considerable human hardship.

It was toward the end of this frigid period that the snowy winters (unusual today) in southern England became the backdrop for the tales of Charles Dickens and other authors. If it had been written today, A Christmas Carol would more likely have taken place under foggy and rainy skies. For Dickens and his contemporaries, however, "normal" winters were probably more severe than those of today. (For the purists out there, the early part of Dickens' formative years -- roughly 1812-1820 -- largely coincided with the coldest decade of the Little Ice Age and had a major influence on his future novels. The winters of other decades, both before and after this period, did not seem to be as severe.)

What is "normal" weather, then, for the Washington area? I think we would all agree that it is hot and it is cold; it is windy and it is calm; it is rainy and it is snowy. It's all of these, in small and in large doses. It is, in fact, the "abnormal" weather of the news media.

By Don Lipman  | April 9, 2010; 11:00 AM ET
Categories:  Lipman, Local Climate  
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Next: PM Update: Cool breezes through tonight


I guess today is a return to "normal" spring conditions, though yesterday's heat and pollen were harder to take...As I posted earlier this week, I spent two springs at grad school in Knoxville in the early 1970's, and can't recall the pollen down there being worse than it is around here. Knoxville does have the same problem we have here: an extended pollen season due to varying tree blooming times with elevation nearby [Great Smoky Mountains & Cumberland Plateau to be exact].

Posted by: Bombo47jea | April 9, 2010 11:50 AM | Report abuse

Maybe its just an optical illusion, but it seems that the records sort of converge a bit towards the averages as we head towards the solstice.

Posted by: dhb2 | April 9, 2010 12:10 PM | Report abuse

I think the DC area has great weather. It's great in that there are plenty of sunny days, yet you get the full force of all four seasons, so there's lots of variation.

We get arctic cold, buffalo snow, Desert Heat, Humid Heat, Chicago wind, Kansas Hail, Seattle like rain periods, and the occasional Hurricane and tornado impact.

So I feel truly blessed to be a DC area resident as a weather enthusiast- one who also enjoys "boring" sunny days as well.

Posted by: markinva2 | April 9, 2010 1:11 PM | Report abuse

markinva2 - glad someone loves DC weather as much as I do!

Posted by: Camden-CapitalWeatherGang | April 9, 2010 2:00 PM | Report abuse

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