Temperatures compared with today’s normal, from the 1870s (top row) to 2010s (bottom row) in D.C. Departures can be a maximum of plus or minus 30 before being cropped. See a very large size.

At first glance, the squiggly lines above might be a seismograph. But this isn’t the Capital Earthquake Gang.

Upon further inspection, the colors might give it away.

Once I tell you red is warm and blue is cool, a fact you might have been able to deduce yourself, the picture becomes a little clearer. Pointing out that each row is a decade of temperature data, the veil is lifted.

The image above illustrates the entire modern temperature record for D.C., in terms of departure from average. In this case (and all cases) NOAA’s average temperature record is based on data from 1981 to 2010.

What emerges is a portrait of Washington’s climate over the past 15 decades. Think of it as weather art.

The data here begins on Jan. 1, 1872. This was back when D.C.’s weather readings were gathered downtown, at a location on M Street NW. In the mid-1940s, the observation location was moved to where it remains today — National Airport.

The graph highlights at least a few things. Among the most apparent to me are:

  • There’s a clear shift from a lot of blue in the late 1800s to a lot of red recently. I’ve now done this at a few stations. The cool to warm shift is apparent across the country. That said, these long-term stations are generally not used in climate change studies, because they are comprised of more than one location “threaded” together as a historical record. To me, If it’s good enough for record keeping, it’s good enough to look at. In the early part of the record, below normal days were about 65 percent of days. In the 2010s, they are about 40 percent of the record so far.
  • The biggest anomalies around here happen in winter. The most extreme temperature departures in either cold or warm direction happen predominantly in winter. This is easy to simplify in thinking that it’s quite a bit easier to warm an average high of 45 in January another 20-degrees than it is warming an average high of 89 in July another 20-degrees. At least we hope it is. No 109s here yet, but plenty of 65 (or higher) in winter.
  • Seasonal and sub-seasonal influences are common. This doesn’t seem to be quite as big of an issue in D.C. as at other locations. In some, you can quite easily find each year, because warm and cool anomalies seem to always cluster around the same time. In D.C., warmer than normal days are more common and more bunchy in summer and fall, while colder than normal temperatures are now most common in spring, with winter not all that much more frequent than any other season.

Beyond any lessons or rules to the data, we can also zoom in to see some neat historical stuff. One is that we’ve had big heat, even way back when. Let’s go to a full crop of the 1930s. The image below shows a range of January 1930 to early March 1932. That’s a lot of red.


The early 1930s, including a second warmest on record January 1932, and too many hundreds in 1930. Departures can be a maximum of plus or minus 30 before being cropped.

Despite now being almost a century behind us, the 1930s was known for heat. While the hardest hit areas of drought and high temperatures were over the central United States, where the Dust Bowl would eventually take hold, the torrid conditions made it to Washington at times as well.

The record holder for the most days of 100-degrees or higher in the city is still 1930, with 11 that summer. On July 20 of that year, D.C. hit 106 — one of two times its done so, the other in August 1918.

And while it was alluded to above, the sea of red in this decade is worth a close-up. The 2010s have just been broiling on the whole.


The 2010s so far. Departures can be a maximum of plus or minus 30 before being cropped.

Given that “normal” does indeed continue to rise from update to update, and these days it is probably even notably warmer between updates, the preponderance of reds off an already historically warm 1981-2010 sample is quite astounding.

There are still big cold shots. You can clearly see Polar Vortex events in there, and some were quite notable. But it’s hard to mistake that red both outlasts and overpowers the blue of late. We’ll see if that changes at all ahead.