Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 14:09 GMT le 28 Mars 2012
February 2012 was the globe's 22nd warmest February on record, according to the National Oceanic and Atmospheric Administration's National Climatic Data Center (NCDC). Global temperatures were the 15th warmest on record according to NASA. It was the coolest February since 1994, and the coolest month, relative to average, since January 2008. The relatively cool temperatures were due, in part, to the on-going La Niña event in the Eastern Pacific, which has brought a large amount of cool water to the surface. February 2012 global land temperatures were the 37th warmest on record, and ocean temperatures were the 12th warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were colder than average, the 7th or 13th coldest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH). February temperatures in the stratosphere were the coldest on record. We expect cold temperatures there due to the greenhouse effect and to destruction of ozone due to CFC pollution. Snow cover during February varied dramatically depending on which hemisphere you were in. Eurasia had its third largest snow cover extent in the 46-year period of record, while North America had its fourth lowest. As seen in Figure 1, much of North America and Siberia were much warmer than average, while Europe was considerably colder than average. Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of February in his February 2012 Global Weather Extremes Summary.
Figure 1. Departure of temperature from average for February 2012. Image credit: National Climatic Data Center (NCDC) .
La Niña weakens, almost gone
A borderline weak La Niña event continues in the equatorial Pacific, where sea surface temperatures were approximately 0.5°C below average during February and the the first half of March. NOAA's Climate Prediction Center forecasts that La Niña will be gone by the end of April. The majority of the El Niño computer models predict neutral conditions for this fall, during the August - September - October peak of hurricane season, though 32% of the models predict an El Niño will develop. El Niño conditions tend to decrease Atlantic hurricane activity, by increasing wind shear over the tropical Atlantic.
February Arctic sea ice extent fifth lowest on record
Arctic sea ice extent was at its fifth lowest extent on record in February, according to the National Snow and Ice Data Center. Continuing the pattern established in January, conditions differed greatly between the Atlantic and Pacific sides of the Arctic. On the Atlantic side, especially in the Barents Sea, air temperatures were higher than average and ice extent was unusually low. February ice extent for the Barents Sea was the lowest in the satellite record, due to air temperatures that ranged from 4 - 8°C (7 - 14°F) above average at the 925 mb level (about 3000 feet above sea level). In contrast, on the Pacific side, February ice extent in the Bering Sea was the second highest in the satellite record, paired with air temperatures that were 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) below average at the 925 mb level. Satellite sea ice records date back to 1979.
Figure 2. Record-setting hailstone from the Hawaii 'supercell' thunderstorm that hit the Hawaiian island of Oahu on March 9, 2012. Image credit: NOAA/National Weather Service.
Huge hailstone sets Hawaii record
A hailstone with the diameter of roughly that of a grapefruit that hit Oahu on March 9, 2012, has been confirmed as the largest hailstone on record for the state of Hawaii, according to NOAA. The record-setting hailstone was dropped by a “supercell” thunderstorm on the windward side of Oahu. There were numerous reports of hail with diameters of 2 to 3 inches and greater. Hail the size of a penny (diameter of 3/4 inch) or quarter (diameter of one inch) has been reported in Hawaii only eight times since records began, and there is no record of hail larger than 1 inch in diameter. Hail the size of golf balls and baseballs can only form within intense thunderstorms called supercells. These supercells need warm, moist air to rise into progressively colder, drier air, as well as winds changing direction and increasing speed with increasing height off the ground. For both sets of conditions to exist at the same time in Hawaii is extremely rare, but that did occur on March 9. Conditions that day were ideal for a supercell to form, and the storm looked very much like supercell thunderstorms common in the Central U.S. during spring. Supercells can also produce tornadoes, another rarity in Hawaii. The same hail-producing supercell produced a confirmed EF-0 tornado with winds of 60-70 mph in Lanikai and Enchanted Lakes on Oahu.
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