April 2012 was the globe’s 5th warmest April on record, according to the National Oceanic and Atmospheric Administration’s National Climatic Data Center (NCDC). NASA rated April 2012 as the 4th warmest April on record. April 2012 global land temperatures were the 2nd warmest on record, and the Northern Hemisphere land surface temperature was 1.74°C (3.13°F) above the 20th century average, marking the warmest April since records began in 1880. Global ocean temperatures were the 11th warmest on record, and April 2012 was the 427th consecutive month with ocean temperatures warmer than the 20th century average. The last time the ocean temperatures were below average was September 1976. The increase in global temperatures relative to average compared to March 2012 (16th warmest March on record) was due, in part, to warming waters in the Eastern Pacific, due to the La Niña event that ended in April. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were 6th or 4th warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH). April temperatures in the stratosphere were the 1st to 4th coldest on record. We expect cold temperatures there due to the greenhouse effect and to destruction of ozone due to CFC pollution. Northern Hemisphere snow cover during April was 4th smallest in the 46-year record. Wunderground’s weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of April in his April 2012 Global Weather Extremes Summary. Notably, national heat records (for warmest April temperature on record) occurred in the United States (a tie), Germany, Austria, Poland, Belarus, Lithuania, Moldova, Hungry, Croatia, Ukraine, and Slovakia as well as the cities of Moscow and Munich.

Figure 1. Departure of temperature from average for April 2012. The most notable extremes were the warmth observed across Russia, the United States, Alaska, and parts of the Middle East and eastern Europe. There were no land areas with large-scale cold conditions of note. Image credit: National Climatic Data Center (NCDC) .

La Niña officially ends
According to NOAA’s Climate Prediction Center (CPC), La Niña conditions are no longer present in the equatorial Pacific, where sea surface temperatures were approximately average as of May 13. The threshold for a La Niña is for these temperatures to be 0.5°C below average or cooler. CPC forecasts that neutral conditions will persist though the summer, with a 41% chance of an El Niño event developing in time for the August – September – October peak of hurricane season. El Niño conditions tend to decrease Atlantic hurricane activity, by increasing wind shear over the tropical Atlantic.

Figure 2. Arctic sea ice extent in 2012 (blue line) compared to the average (thick grey line.) The record low year of 2007 (dashed green line) is also shown. Arctic sea ice was near average during April, but has fallen well below average during the first half of May. Image credit: National Snow and Ice Data Center (NSIDC).

April Arctic sea ice extent near average
Arctic sea ice extent was near average in April 2012, the 17th lowest (18th greatest) extent in the 35-year satellite record, according to the National Snow and Ice Data Center (NSIDC). This was the largest April Arctic sea ice extent since 2001. However, ice in the Arctic is increasingly young, thin ice, which will make it easy for this year’s ice to melt away to near-record low levels this summer, if warmer than average weather occurs in the Arctic.

Figure 2. Mt. St. Helens in Washington State erupting on May 18, 1980. Image credit: USGS.

Anniversary of the eruption of Mt. St. Helens
Today is the 32nd anniversary of the May 18th, 1980 eruption of Mt. St. Helens in Washington State. To mark the occasion, NASA has put together a cool Landsat satellite time lapse of 32 years of regrowth of surrounding forest. The USGS has an extensive informational site on the eruption.