For much of the U.S., 2012 was the year without a winter. NOAA announced today that not only was March the warmest on record in the U.S. (lower 48 states), but so too was the entire January-February-March period.
After the onslaught of daily and monthly records, the March nationwide record comes as no surprise. The average temperature across the country was an incredible 8.6 degrees above the 20th century average (half a degree warmer than the previous record from 1910). Aside from January, 2006, no month on record had surpassed its average by such a large margin.
Here are some more amazing details about the March temperatures in the Lower 48 according to NOAA:
* 25 states east of the Rockies had their warmest March on record. An additional 15 states had monthly temperatures ranking among their ten warmest.
* There were 21 instances of low (nighttime) temperatures being as warm, or warmer, than the existing record daytime temperature for a given date. (list)
* Four locations established a new daily record high by 30 or more degrees (list)
* There were 15,292 warm temperature records broken (compared to just 890 records lows).
* Hundreds of locations broke all-time March records.
More information: NOAA March State of the Climate Report
Animation of over 15,000 daily high temperature records during March from NOAA.
Exceptionally warm January through March
While not as extreme, unseasonably mild weather preceded the March heat blast over much of the Lower 48.
For the first quarter of 2012 (January-March period), the record-breaking temperature in the Lower 48 was 6.0 degrees above average. All 25 states east of the Rockies had their warmest first quarter on record, including the cities of Chicago, Boston, and Washington, D.C. Not a single state was cooler than average.
The U.S. Climate Extremes Index, which tracks extremes in temperature, precipitation and drought (also includes tropical storms during hurricane season), was highest on record for the period - largely due to all of the warm weather records.
Weather patterns behind warm weather
During the second half of March, a massive ridge in the jet stream - or a heat dome - developed over the eastern part of the U.S. This long-lasting feature led to an incredible blitz of heat records. The Weather Channel’s Stu Ostro confirmed this heat dome (as measured by an indicator of pressure at about 18,000 feet, known as 500 mb heights) was the strongest on record (since 1948) so early in the year in the region affected.
Prior to March, the warmth in January and February resulted mostly from a pattern that kept most of the bitter Arctic air locked up towards the North Pole. Much of the continental U.S. remained under the influence of mild west to east flow (off the Pacific Ocean) with only brief southward excursions of Arctic air.
Contributions from global warming
An analysis from NOAA suggests the March heat wave was intensified by elevated greenhouse gas concentrations from human activities:
“Our current estimate of the impact of GHG [greenhouse gas] forcing is that it likely contributed on the order of 5% to 10% of the magnitude of the heat wave during 12-23 March,” it said.
While noting there is a degree of “randomness” in the occurrence of such heat waves, NOAA cautioned their odds are “growing” as greenhouse gas levels build up in the atmosphere.
“It’s [the warm weather] been ongoing for several months,” Jake Crouch, a climate scientist at NOAA’s National Climatic Data Center, told the Associated Press.
Indeed, NOAA found the cold season spanning October 2011-March 2012 was second warmest on record in the Lower 48 and that the 12 month period from April 2011-March 2012 was the top warmest on record.