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Warmest Ever? You Bet. March Temps Fry All Records

Due to the extraordinary heat wave that sent temperatures soaring to summer-like levels across the eastern two-thirds of the country, March was officially the warmest such month in history for the Lower 48 states, the National Climatic Data Center (NCDC) announced Monday.

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The heat wave was unprecedented in its scope and magnitude for so early in the year, with many locations breaking longstanding records by up to 40 degrees Fahrenheit. The U.S. surface temperature record dates back to 1895.

Several top climate scientists interviewed by Climate Central said global warming may have made the heat wave more likely to occur and more intense than it otherwise would have been, as some argue has happened with other recent heat waves, such as the deadly Russian heat wave in 2010 and the European heat wave in 2003

Detailed studies of how manmade climate change influenced the March heat event have not yet been completed, since such research takes several months or more of model experiments and analysis to complete. A new analysis from scientists at the National Oceanic and Atmospheric Administration (NOAA) concluded that global warming "appreciably increased the odds of a record March heatwave occurring," and contributed to the intensity of the event, along with the influence of natural climate variability.

Surface temperature departures from average during March 2012. Credit: NCDC. Click on the image for a larger version.

A recent report from the U.N. Intergovernmental Panel on Climate Change found a high likelihood that extreme heat events are already becoming more common and severe in many parts of the world, partly as a result of manmade global warming, a trend that is likely to continue during the coming decades.

A forthcoming paper from NASA climate scientist James Hansen and colleagues argues that global warming is "loading the climate dice" and making heat extremes far more common.

The average temperature in March for the contiguous U.S. was 8.6 degrees F above average, an incredibly large departure from normal, beating March 1910 by a half degree. Of the more than 1,400 months that have passed since weather records began in 1895, only one other month - January 2006 - had a greater departure from its typical average temperature.

March 2012 temperature departures from average in the Midwest. Credit: Midwest Regional Climate Center.

Due to the heat wave, 25 states east of the Rockies had their warmest March on record, while another 15 states had monthly temperatures ranking among their 10 warmest.

The persistent warmth smashed records from the Upper Midwest to the Northeast, with a total of 15,292 warm-temperature records broken, the NCDC reported. Every state except Alaska and Hawaii experienced a record-warm daily temperature during March.

Of these records, 7,775 were daytime-high temperature records, and 7,517 were warm-nighttime low temperature records. In 21 cases, nighttime temperatures were as warm, or warmer, than the existing record-high temperature for that date. In Rochester, Minn., for example, the temperature only dropped to 62 degrees on March 18, breaking the previous record high for the date of 60.

During the height of the heat wave between March 14-22, Chicago broke or tied its record-high temperature for nine straight days, including the most 80 degree readings ever recorded during the month of March. International Falls, Minn., — the “icebox of the nation”— saw record highs broken or tied on every day except one from March 10-22.

In recent years, record daily highs have been outpacing record daily lows in a pattern that has been shown to be inconsistent with natural climate variability alone. So far in 2012, the daily record-high to record-low ratio has been about 17-to-1. For monthly record highs compared to monthly record lows the ratio has been a lopsided 33-to-1 in favor of warm temperature records. If the climate were not warming, one would expect the ratios to be, on average, closer to 1-to-1.

March 2012 temperature departures from average in the Northeast. Credit: Northeast Regional Climate Center.

The year-to-date is running as the warmest such period on record for the contiguous U.S., with an average temperature that was 6 degrees above the long-term average, and 1.4 degrees above the previous record. Typically, records like this one are broken by a few tenths of a degree, so this large margin is unusual. 

For the January-to-March period, 25 states east of the Rockies had three-month average temperatures that were the warmest on record. Cities that had a record warm January-to-March period include Boston, Chicago, and Washington D.C.. No state in the Lower 48 had below average three-month temperatures.

The heat in March followed the fourth-mildest winter on record, and the second-warmest summer. Since April 2011, the continental U.S. has experienced its hottest one-year period on record. The 12-month running average temperature was 55.4 degrees F, which was 2.6 degrees above average, the NCDC stated. 

As a sign of how extreme this year has been so far, the Climate Extremes Index, which tracks the temperature, precipitation, drought and hurricane-related extremes in the U.S., was the highest value on record for the period, at nearly twice the long-term average. The unusually warm temperatures were the main reason for this, according to the NCDC.

Although millions of Americans basked in the early-season warmth, the weather wasn’t completely benign, since the mild air helped spawn deadly March tornadoes, with more than 220 preliminary tornado reports. A typical March averages just 80 tornadoes. The March 2-3 outbreak in the Ohio Valley and Southeast killed 40 and caused $1.5 billion in total losses, making it the first billion dollar natural disaster of 2012.