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Rare Beast: For Many, March Was Warmer Than April

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March 2012 is the month that just keeps on giving when it comes to warm temperature records in the United States. Given the widespread, long-lasting and unprecedented heat wave, March came in like a lamb, and went out like . . . a grilled lamb. It was the warmest such month on record in the Lower 48 states, exceeding the average by a whopping 8.6 degrees F.

That heat has helped nearly 140 climate reporting stations, including in major cities such as Chicago, Detroit and Milwaukee, achieve a rare feat: record a cooler April to date compared to March, according to a Climate Central analysis of temperature data through April 24.

Locations where average temperatures during April 2012 are likely to be cooler than March was, according to Climate Central research. Click for an interactive version.

It is extremely rare for the average temperature during April to be cooler than March. For example, in Rockford, Illi., located west of Chicago, that had never happened, and in Chicago, it had occured only once before, way back in 1907.

Typically, April in Rockford averages about 13°F warmer than March. Yet this year, because March was so warm, it managed to even eclipse what has been a warmer-than-average April.

“It is incredible that April will end up above average, yet still cooler than March, which is just another testament to how extraordinarily unusual our March warmth was this year,” said a statement from the National Weather Service Forecast Office in Chicago. According to the NWS, based on forecasts for the next week, it's likely that the role reversal will hold once the numbers are crunched for the entire month.

During March, Chicago broke or tied daily high-temperature records on nine straight days from March 14-22 — the second-longest stretch of daily temperature records of any type for the city dating back to 1871.

According to the National Weather Service, the average temperature in Chicago during March was 53.5, compared with an average of 50.9 so far this April. Typically in Chicago,  the month of April has an average temperature of 49.6, indicating that April 2012 is running above average, just not warm enough to catch up with what was a record-shattering March.

Map of global temperature departures from average during March 2012, showing how much the U.S. and Canadian heat wave stands out. Credit: NOAA. Click on the image for a larger version.

The situation is similar in Milwaukee, where the average temperature during April has been nearly 2°F cooler than March. According to a Climate Central analysis, other locations where March was warmer than April include Columbus, Louisville, Omaha, Neb., and Sioux Falls, S.D.

April has seen its fair share of heat as well, although it has mainly affected the Western states. Death Valley, Calif., hit 113°F on April 22, the earliest it has ever been so hot there, and tied for the hottest April temperature ever recorded in the U.S.

The U.S. and Canada were the warmest areas in the world during March. When other land areas and the oceans are factored in, March was the 16th warmest such month on record globally.

For March as a whole, more than 7,000 daily record-high temperatures were set or tied, and a nearly equal amount of warm overnight low temperatures were reached. 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. If the climate were not warming, one would expect the ratios to be closer to 1-to-1. 

Climate scientists who specialize in the study of extreme weather and climate events have said they suspect that manmade global warming increased the odds for the March heat wave and made it more severe than it otherwise would have been, although studies are still ongoing.

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