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Sunday, November 11, 2012

Despite a cool October, U.S. on track for its warmest year on record, beating out 1998

by Jeff Masters, PhD, November 10, 2012

For the first time in sixteen months, the contiguous U.S. has had a month with below-average temperatures, with October 2012 ranking as the 44th coldest (73rd warmest) October since record keeping began in 1895, said NOAA's National Climatic Data Center (NCDC) in their latest State of the Climate report. Temperature extremes were scarce in October, as no states had a top-ten warmest or coldest October. Despite the cool October temperatures, the year-to-date period of January-October was the warmest such period on record for the contiguous U.S. -- a remarkable 1.1 °F above the previous record. Even if the remainder of 2012 ranks historically in the coldest one-third of November-Decembers ever seen, 2012 will beat out 1998 for warmest year. The first ten days of November have been warmer than average, and the next two weeks are predicted to also average out on the warm side, so it appears likely that we will have to have our coldest December on record in order to keep 2012 from setting the new mark. The November 2011-October 2012 period was the warmest such 12-month period on record for the contiguous U.S., and the seven warmest 12-month periods since record keeping began in 1895 have all ended during 2012. 

Texas had their 9th driest October on record last month, and Washington, Michigan, Ohio, Maine, and Maryland had top-10 wettest Octobers; Delaware had their wettest October on record, thanks to rains from Hurricane Sandy. The area of the U.S. experiencing moderate-to-exceptional drought shrank from 65% at the beginning of October to 59% by November 6, with drought conditions improving across parts of the Midwest and Northeast, but worsening across portions of the Northern Rockies.

Figure 1. Year-to-date temperatures for the contiguous U.S. through October, compared to the previous record warmest years in U.S. history. The year-to-date period (thick black line) is 1.1 °F warmer than the previous record, set in 1998. Even if the remainder of 2012 ranks historically in the coldest one-third of November-Decembers on record (dark blue line), 2012 will beat out 1998 for the warmest year on record. The data for 2012 are preliminary. Image credit: NOAA/NCDC.

Second most extreme January-October period on record
The year-to-date period was the second most extreme on record in the U.S., according to NOAA's U.S. Climate Extremes Index (CEI), which tracks the percentage area of the contiguous U.S. experiencing top-10% and bottom-10% extremes in temperature, precipitation, and drought. The CEI was 38% during the year-to-date January-October period. This was exceeded only in 1998 (41%), and was nearly double the average value of 20%. Remarkably, 85% of the contiguous U.S. had maximum temperatures that were in the warmest 10% historically during the first ten months of 2012, and 76% of the U.S. of the U.S. had warm minimum temperatures in the top 10%. Both are records. The percentage area of the U.S. experiencing top-10% drought conditions was 28%, which was the 7th greatest since 1910. Only droughts in 2002, 1954-1956, and during the Dust Bowl years of 1931 and 1934 were more extreme for the January-October period. Heavy one-day downpours were below average, though, with 8% of nation experiencing top-10% extremes in October 2012, compared to an average of 10%.

Figure 2. NOAA's U.S. Climate Extremes Index (CEI) for January-October shows that 2012 had the second most extreme first ten months of the year on record, with 38% of the contiguous U.S. experiencing top-10% extreme weather.

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