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 , 2:30 PM GMT on November 23, 2009
The globe recorded its sixth warmest October since record keeping began in 1880, according to NOAA's National Climatic Data Center. NASA's Goddard Institute for Space Studies rated October 2009 as the 2nd warmest October on record, falling 0.06°C short of the record set in 2005, while the UK HADCRUT3 data set rated October the 7th warmest (this data set does not include most of the Arctic, Antarctic, and Africa, where there are few land stations). NOAA rated the year-to-date period, January - October 2009, as the fifth warmest such period on record. The October satellite-measured temperatures for the lowest 8 km of the atmosphere were 6th - 7th warmest on record. Global ocean Sea Surface Temperature (SST) anomalies were the 5th warmest on record.
Figure 1. Departure of temperature from average for October 2009. Image credit: National Climatic Data Center.
Third coldest and top wettest October on record for the U.S.
For the contiguous U.S., the average October temperature was 4.0°F below average, making it the 3rd coldest October in the 115-year record, according to the National Climatic Data Center. The cold was centered in the Midwest, where Oklahoma had its coolest October on record and ten other states had a top five coolest October. The nationwide precipitation of 4.15 inches was nearly double the long-term average of 2.11 inches. Three states (Iowa, Arkansas, and Louisiana) saw their record wettest October. Fourteen other states had precipitation readings ranking in their top five category. Only three states (Florida, Utah, and Arizona) saw below normal precipitation. Arkansas continued its remarkable run of wetness in 2009. The state has seen four months with top three precipitation ranks this year (May, 1st wettest; July, 3rd wettest; September, 2nd wettest; October, 1st wettest). As a result, the state's year-to-date average is the wettest in 115 years of record keeping. This contrasted with persistent dryness in Arizona, which saw its second-driest year-to-date period.
U.S. drought decreases
At the end of October, 12% of the contiguous United States was in moderate-to-exceptional drought. This is the second-smallest drought footprint of the decade, based on the U.S. Drought Monitor. Major drought episodes in California and South Texas improved significantly. Drought conditions emerged across much of Arizona. About 45% of the contiguous United States had moderately-to-extremely wet conditions at the end of October, according to the Palmer Index (a well-known index that measures both drought intensity and wet spell intensity). This is the largest such footprint since February 2005.
As I commented in a post earlier this year, drought, on average, has not been increasing in the U.S. over the past few decades. The exception is the Southwest U.S. Increased drought is my top concern in regards to the potential effects of climate change over the next 40 years, and I am pleased to see that so far we have not seen increased drought in the U.S. A recent paper by Andreadis et al., 2006, summed up 20th century drought in the U.S. thusly: "Droughts have, for the most part, become shorter, less frequent, and cover a smaller portion of the country over the last century. The main exception is the Southwest and parts of the interior of the West, where, notwithstanding increased precipitation (and in some cases increased soil moisture and runoff), increased temperature has led to trends in drought characteristics that are mostly opposite to those for the rest of the country especially in the case of drought duration and severity, which have increased."
However, drought may be increasing for the world as a whole. Dai and Trenberth (2004) showed that areas experiencing the three highest categories of drought--severe, extreme, and exceptional--more than doubled (from about 12% to 30%) since the 1970s, with a large jump in the early 1980s due to an El Niño-related precipitation decrease over land, and subsequent increases primarily due to warming temperatures. I've neglected drought in my blogs, and plan to do a thorough investigation and report on the latest research now that hurricane season is over.
U.S. fire activity
October, like September, saw below-normal fire activity in all respects. A total of 3,207 fires burned about 158,000 acres in October, according to the National Interagency Coordination Center. Each of these values is below this decade's average for October.
Strong El Niño conditions develop
El Niño conditions intensified from moderate to strong over the tropical Eastern Pacific in October. Ocean temperatures in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", were at 1.7°C above average on November 15, just above the 1.5°C threshold for a strong El Niño, according to the Australian Bureau of Meteorology. NOAA's Climate Prediction Center is maintaining an El Niño Advisory. El Niño conditions appear to have stabilized over the past week, and no further intensification of El Niño is likely for the remainder of November. Model forecasts favor moderate to strong El Niño conditions during the Northern Hemisphere Winter of 2009 - 2010.
October sea ice extent in the Arctic 2nd lowest on record
October 2009 Northern Hemisphere sea ice extent was the 2nd lowest since satellite measurements began in 1979, according to the National Snow and Ice Data Center (NSIDC). Only 2007 saw lower Arctic sea ice extent. During the first two weeks of November, Arctic ice extent decreased below the 2007 record minimum, according to data from the National Snow and Ice Data Center. The record low ice extent this month is the first extended period of record minimum Arctic sea ice since 2007. The new record minimum suggests that the gains in ice seen over the past two years were probably a temporary fluctuation due to normal year-to-year variability in the weather, and that the long-term Arctic sea ice decline observed since the 1970s is continuing.
Figure 2. Departure of Arctic sea ice from average for October 2009. Image credit: National Snow and Ice Data Center (NSIDC).
Andreadis, K. M. Lettenmaier, D. P., "Trends in 20th century drought over the continental United States", Geo. Res. Letters 33, 10, L10403, DOI 10.1029/2006GL025711
Dai A., K.E. Trenberth, and T. Qian, 2004: A global data set of Palmer Drought Severity Index for 18702002: Relationship with soil moisture and effects of surface warming", J. Hydrometeorol., 5, 11171130.
I'm working on a rather lengthy analysis of the global warming scientist vs. skeptic controversy, including last week's hacked email affair. I'll post it when I get it done, most likely on Tuesday, but perhaps Wednesday.
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