Dr. Jeff Masters' WunderBlog

Figure 2. Three of the top ten warmest 12-month periods in the contiguous U.S. since 1895 have occurred since April 2011. Image credit: NOAA/NCDC.

Figure 3. The average temperature during January - May 2012 was the warmest on record: 5°F above the 20th century average for the period, and 1.3°F above the previous record set in 2000. January - May temperatures have been rising at about 1.8°F per century since 1895. Image credit: NOAA/NCDC.

Second warmest May, warmest year-to-date period on record
May 2012 was the second warmest May in the contiguous U.S. since record keeping began in 1895. Twenty-six states had a top-ten warmest May, and no states had a top-ten coolest May. The January - May 2012 period was the warmest January - May period since record keeping began in 1895, with temperatures 5°F above the 20th century average for the period. This broke the previous record set in 2000 by an unusually large margin--1.3°F.

Figure 4. NOAA's U.S. Climate Extremes Index (CEI) for spring (March - April - May) shows that 2012 had the most extreme spring on record, with 44% of the contiguous U.S. experiencing top-10% extreme weather.

Most extreme spring and January - May period on record
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, was 44% during the spring March - April - May period. This is more than twice the average value, and spring 2012 was the most extreme season of any kind in U.S. history. A list of the top five most extreme seasons since 1910, as computed using the CEI, show that two of the three most extreme seasons in U.S. history occurred in the past 12 months:

Spring 2012: 44%
Winter 1979: 42%
Summer 2011: 39%
Fall 1985: 39%
Spring 1934: 38%

Remarkably, 81% of the contiguous U.S. had maximum temperatures that were in the warmest 10% historically during spring 2012, and 71% of the U.S. of the U.S. had warm minimum temperatures in the top 10%. The percentage area of the U.S. experiencing top-10% drought conditions during spring was 18%, which was the 19th greatest since 1910. Extremes in 1-day spring heavy precipitation events were the 8th largest on record. The year-to-date January - May period was also the most extreme such period in U.S. history, with a CEI of 43%. Climate change theory predicts that, in general, the climate should warm, wet areas should get wetter, and dry areas should get drier. The spring 2012 Climate Extremes Index reflects this pattern.

Have a great weekend, everyone, and I'll be back Monday with a new post. None of the computer models is predicting tropical cyclone formation in the Atlantic through June 15.

Jeff Masters