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Above-average precipitation throughout much of the United States during the past three months led to improving drought conditions in many areas, according to scientists at the National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center (NCDC) in Asheville, N.C. NOAA is part of the Commerce Department.
Twenty-four percent of the contiguous United States was in moderate-to-extreme drought in April, down from 37 percent in January and 50 percent during the summer of 2002, based on a widely used measure of drought severity, the Palmer Drought Index.
NCDC researchers said precipitation averaged across the contiguous United States was 0.5 inch (12.7 mm) above the 1895-2003 long-term mean for the February through April three-month period, based on preliminary data. Twenty seven states were significantly wetter than average and 11 states were significantly drier than average. Wetter-than-average conditions were prevalent in the Mid-Atlantic, Southeast and in most states of the western United States. Near-average to drier-than-average conditions stretched from Maine to the Upper Midwest and southwest to Texas.
The precipitation helped alleviate extremely dry conditions in many areas, but the rain and snowfall were not sufficient to end the drought in many parts of the West, where severe drought has occurred for much of the past three to five years. In Colorado, which had its driest year on record in 2002, a single snow storm in March brought a near-record snowfall of 32 inches to Denver Stapleton Airport and totals exceeding 80 inches in higher-elevation locations to the west.
Snow pack, an important source of water for western states, was near or above average at the end of April in much of the front range of the Rocky Mountains from Montana to Colorado and the Sierra Mountains, but snow pack remained below average in large parts of the West. Reservoir storage was also below average in every western state except Washington at the end of April, and river flows remained below average in a large part of the western two-thirds of the nation.
In Montana, where conditions in parts of the state during the summer of 2002 were similar to those experienced during the Dust Bowl years of the 1930's, above average precipitation during the past several months led to a marked improvement in drought conditions. However, according to the U.S. Drought Monitor, severe drought continued to affect a large part of the state at the end of April.
Based on the Palmer Drought Index, the percent of the West in moderate to extreme drought decreased from 81 percent in November 2002 to 44 percent in April. The most widespread drought in the instrumental record occurred in July of 1934, when 97 percent of the West and 80 percent of the contiguous United States were in moderate to extreme drought. The percent of the contiguous United States in moderate to extreme drought fell to 24 percent in April.
Temperatures during the February-April 2003 period were near average to slightly warmer than average across most of the country. The Northeast was the only region with significantly cooler-than-average temperatures. For the contiguous United States as a whole the February-April temperature was 43.3 F (6.3 C), slightly warmer than the 1895-2003 mean. In Alaska the three-month period was 6.0 F (3.3 C) warmer than the 1971-2000 average. During the past 25 years, temperatures in Alaska have averaged 3.2 F (1.8 C) warmer than during the preceding 50 years.
The moderate El Niño episode that began in 2002 weakened during the February-April period, while the average global temperature for combined land and ocean surfaces (based on preliminary data) during April was 0.9 F (0.5 C) above the 1880-2002 long-term mean. This was the fourth warmest April but 0.4 F (0.2 C) cooler than the record warm April which occurred near the end of the 1997-98 El Niño episode. The land-surface temperature average was the seventh warmest on record for April (1.4 F above average), and the global ocean-surface temperature was 0.7 F above average, approximately 0.2 F cooler than April 1998. The year-to-date global average for combined land and ocean surfaces was the third warmest on record.
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