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For Litany of U.S. Cities, 2012 Temps Are Unprecedented

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So far this year, the U.S. is running a distinct fever, as the lower 48 states had its warmest January-to-May period on record, according to the National Oceanic and Atmospheric Administration (NOAA). Other longstanding records have fallen as well, including the record for warmest spring, which dated back to 1910 and was smashed by 2°F, warmest 12-month period, and largest seasonal departure from average.

Taking a deeper dive into the temperature statistics reveals fascinating insights into just how warm it's been at the local level in many locations. As NOAA stated on its website on Thursday, "In some locations, 2012 temperatures have been so dramatically different that they establish a new "neighborhood" apart from the historical year-to-date temperatures."

The year-to-date numbers were certainly boosted by the unprecedented heat wave that took place during March, when several thousand warm temperature records were shattered from the Rocky Mountain states on eastward. Global warming raises the odds of heat extremes, and natural variability has favored warmer-than-average conditions so far this year as well. This has had a profound effect at the local level this year.

Take Chicago, for example. With a January-to-May average temperature that was 7.1°F above average, or 3.1 standard deviations above the 1981-2000 norm, this year so far stands in a class of its own — the warmest in the past 54 years of recordkeeping. NOAA's chart (click on it to open a larger version) clearly illustrates this, with the bright red line depicting 2012 temperatures.

Haywood plot showing how temperatures in 2012 so far stack up against previous years for Chicago. Click on image for a Credit: NOAA/NCDC.

Here's NOAA's technical explanation for how such charts, called "Haywood Plots", are calculated:

The unusualness is based upon the number of standard deviations difference between the 2012 value and the station's average, based on the station's history.

...As you read from left to right, a particular year's trace represents the average of all previous days during that year. For this reason, these plots are often very noisy early in a period (towards the left), but they provide an outstanding representation of unusualness over the whole of the period.

Here's what the chart looks like for St. Paul, Minn., where the January-to-May period came in at 7.5°F above average, for the warmest in 74 years of recordkeeping there.

Haywood plot showing how temperatures in 2012 so far stack up against previous years for St. Paul, MN. Click on image for a Credit: NOAA/NCDC.

It was a similar story in Milwaukee, where January-to-May temperatures were 6.2°F above average, or 2.8 standard deviations above the norm. This made it the warmest such period in 71 years of recordkeeping.

Haywood plot showing how temperatures in 2012 so far stack up against previous years for Milwaukee. Click on image for a Credit: NOAA/NCDC.

In Detroit, January-to-May temperatures averaged 5.8°F above average, or 2.9 standard deviations above the norm, for the warmest such period in 54 years.

Haywood plot showing how temperatures in 2012 so far stack up against previous years for Detroit. Click on image for a Credit: NOAA/NCDC.

Lastly, in New York City's Central Park, where weather records extend further back than at some Midwestern stations, the January-to-May period was 4.7°F above average, making it the warmest such period in 137 years.

Haywood plot showing how temperatures in 2012 so far stack up against previous years for New York. Click on image for a Credit: NOAA/NCDC.

Additional data is available from NOAA's website, showing how temperatures compared at other cities across the country. There were precious few places that had cooler-than-average temperatures so far this year, the vast majority of them located in the West and Northwest. One exception is Portland, Maine, which somehow beat the heat — with an average temperature of 0.7°F below average. Portland residents can probably thank the cold waters of the Atlantic Ocean for that.

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