Warmest April on record for the globe
The globe recorded its warmest April since record keeping began in 1880, according to the National Oceanic and Atmospheric Administration's (NOAA's) National Climatic Data Center. The April temperature anomaly of 0.76°C (1.37°F) beat the previous record set in 1998 by 0.05°C. The is the second consecutive warmest month on record. NASA's Goddard Institute for Space Studies also rated April 2010 as the warmest April on record. The year-to-date period, January - April, is the warmest such period on record, according to both NOAA and NASA. NASA also rated the last 12-month period (May 2009 - April 2010) as the warmest 12-month period on record. April 2010 global ocean temperatures were the warmest on record for the 2nd month in a row, while land temperatures were the 3rd warmest. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 2nd warmest on record in April, according to both the University of Alabama Huntsville (UAH) and Remote Sensing Systems (RSS) groups.
For those interested, NCDC has a page of notable weather highlights from April 2010.
Figure 1. Departure of temperature from average for April 2010. Image credit: NOAA's National Climatic Data Center.
A very warm April for the U.S.
For the contiguous U.S., it was the 14th warmest April in the 116-year record, according to the National Climatic Data Center. California was the coldest state, relative to average, with its 12th coldest April. No state had a top-ten coldest April. Five states had their warmest April on record--Illinois, Maine, Rhode Island, Connecticut, and New Jersey. Sixteen other states had top-ten warmest Aprils.
U.S. precipitation and drought
For the contiguous U.S., April 2010 ranked as the 36th driest in the 116-year record. Louisiana, South Carolina, North Carolina, Virginia, Maryland, Connecticut, and Massachusetts all had top-ten driest Aprils. Only Oregon had a top-ten wet April. At the end of April, 2% of the contiguous United States was in severe-to-exceptional drought. This is the lowest April drought footprint in the U.S. in the past ten years.
El Niño is over
El Niño rapidly weakened during late April and early May, with sea surface temperatures over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", falling 0.65°C in just one month. This brought SSTs into "neutral" conditions, at 0.18°C above average, which is well below the 0.5°C above average threshold to be considered an El Niño, according to the Australian Bureau of Meteorology. The speed of the collapse of El Niño makes it likely that a La Niña event is on its way this summer. This is what happened during the last strong El Niño event in 1998--El Niño collapsed dramatically in May, and a strong La Niña event developed by hurricane season. Ten of the 23 El Niño models (updated as of May 19) are predicting La Niña conditions for hurricane season. The demise of El Niño, coupled with sea surface temperatures in the tropical Atlantic that are currently at record levels, have prompted two major hurricane forecasting groups (tropicalstormrisk.com and Colorado State University) to predict a significantly above average 2010 Atlantic hurricane season. Over the full 160-year period we have records of Atlantic hurricanes, La Niña years have typically had more hurricanes, and more strong hurricanes, compared to neutral years. However, since 1995, there hasn't been any difference between neutral and La Niña years in terms of hurricane activity.
April sea ice extent in the Arctic near average in April
April 2010 Northern Hemisphere sea ice extent was the 15th lowest (or 18th greatest) since satellite measurements began in 1979, so was near average. However, the ice volume anomaly was at a record low at the end of April, according to University of Washington Polar Ice Center. Wind patterns this spring have pushed a great deal of the oldest ice out of the Arctic, leaving mostly thin ice that is vulnerable to rapid melting. The first two weeks of May have seen unusual warmth in the Arctic, leading to rapid melting, and ice extent as of May 20 was the 2nd lowest on record, behind 2006, according to the National Snow and Ice Data Center (NSIDC).
I'll be back this afternoon to talk about the oil spill and the tropics. I'm working on a post about how a hurricane passing over the spill might affect the oil. I'll post it if I have time to finish it.