La Niña fades to neutral; April the globe's 4th - 7th warmest on record

April 2011 was the globe's 7th warmest April on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated April the 4th warmest on record, tied with April 2005. April 2011 global ocean temperatures were the 11th warmest on record, and land temperatures were the 6th warmest on record. The UK had its hottest April on record, with rainfall only 21% of average. Huge fires burned through Scotland, England, and Northern Ireland, fanned by strong spring winds.


Figure 1. Departure of temperature from average for April, 2011. Image credit: National Climatic Data Center (NCDC).

La Niña fades to neutral
The La Niña that began in June 2010 is now transitioning to neutral conditions, according to the Climate Prediction Center. Sea surface temperatures (SSTs) in the equatorial Pacific off the coast of South America are now just 0.4°C below average, the first time since June 2010 that these temperatures have not been 0.5°C or more cooler than average, the threshold for a La Niña. However, it is possible that these water could cool a bit again over the next few weeks, so NOAA has not yet declared an official end to this La Niña episode. Equatorial SSTs were 0.5°C below average in the central Pacific, and average to above-average temperatures have emerged in the eastern Pacific. While this signals the end to La Niña, the CPC cautions that the atmosphere is still behaving like La Niña is continuing. An animation of SSTs since February shows the weakening La Niña nicely. Springtime is the most common time for a La Niña event to end; since 1950, half of all La Niñas ended in March, April, or May.

Arctic sea ice 5th lowest on record
Arctic sea ice declined slowly through most of April, and had the 5th lowest extent since satellite record began in 1979, according to the National Snow and Ice Data Center. However, sea ice extent began declining more quickly toward the end of the month, and as of May 16 was the second lowest on record.

I'll have more on the Mississippi River flood next post. If you haven't seen it, read my post, America's Achilles' heel: the Mississippi River Old River Control Structure.

Jeff Masters and Angela Fritz

Angela is a new wunderground hire, with a Masters degree in Meteorology, who will be helping out with my blog and the site's weather education and climate change content.