Average annual temperatures for contiguous U.S. Data from NOAA. ( The Washington Post )

NOAA’s National Climatic Data Center (NCDC) officially crowned 2012 the warm weather king today for the Lower 48 states, and by a lofty margin. The chart-busting average temperature was 55.3 degrees F, one full degree above the previous record set in 1998 and 3.2 degrees F above the 20th century average.

Related: 2012 hottest year on record in continental U.S., NOAA says

Through November, 2012 had been so warm, that December woud have needed to rank coldest on record for the year not to be top warmest. Instead, December cemented 2012’s spot as the warmest on record, ranking 10th warmest on record itself. Records date back to 1895.

An incredible disparity mounted between extremely warm and extremely cold weather. In all, 356 all-time record highs were known to be broken in 2012 compared to just four all-time lows.

The Climate Extremes Index in the contiguous U.S. over time. 2012 ranked second highest on record (NOAA NCDC)

The combination of the exceptional warmth and historic drought conditions placed 2012 as the second most extreme on record, NCDC said. Its Climate Extremes Index - which measures the area of U.S. affected by unusually warm and cold and wet and dry conditions - was nearly twice the average value and only trailed 1988.

Eleven billion dollar weather disasters occurred - headlined by Superstorm Sandy and the drought. This number was second most on record, behind only 2011 - which had 14. However, in large part due to Sandy, the total costs from 2012 are expected to be higher than 2011’s $60 billion sum NCDC said.

Link: 2012 by the numbers in the U.S.

Difference from average annual temperature in 2012 compared to the 1981-2010 average. (NOAA)

The nation’s warmest weather (compared to average) was concentrated in the central part of the U.S. but was so pervasive that only coastal sections of the Pacific Northwest and Alaska had average or below average temperatures. In the contiguous U.S., every state had above average temperatures. Nineteen states had their warmest year on record and an additional 26 states had one of their top 10 warmest years.

2012 contributed to a streak of 16 consecutive months of above average temperatures over the U.S. that started in June 2011.

“That has never occurred [before in U.S. climate records] and is clearly symptomatic of a changing climate,” NCDC’s director Tom Karl said.

The year began very warm with the fourth mildest winter on record followed by a record-setting spring, more than five degrees above average.

The early warmth produced a “tremendous green-up” in corn and soybean growing areas of the Midwest and farmers planted their crops as early they could, Karl said.

But this backfired as temperatures continued to climb and rains diminished. July was the hottest month ever recorded in the U.S. and the summer overall ranked second warmest on record.

“An estimated 99.1 million people experienced 10 or more days of summer temperatures greater than 100°F, nearly one-third of the nation’s population,” NCDC said.

The combination of widespread blistering heat and a sustained period of below average precipitation led to disastrous drought conditions. NCDC provided this detail to put the drought in historic context:

The footprint of drought during 2012 roughly equaled the drought of the 1950s which peaked at approximately 60 percent. The size of the current drought and the drought of the 1950s are smaller than the drought episodes of the 1930s. The current drought has yet to reach the intensity or duration of the 1950s and 1930s national-scale droughts.

Karl stressed that the extreme daytime temperatures were a huge factor in the drought’s severity. In past years, Karl said, large parts of the Midwest had experienced unusually warm nighttime temperatures in recent years, but daytime heat had not been so extreme. But 2012 “reversed that trend” Karl said and as many records were set for daytime warmth as nighttime warmth.

“It’s detrimental for crops when the nighttime temperature doesn’t go below 75 -- and when the daytime temperature goes above upper 80s, ” Karl said.

The warm, dry conditions also stoked widespread, record-setting wildfire activity in the West. Overall, 9.2 million acres burned, third most on record. NCDC reports these details:

The Waldo Canyon fire near Colorado Springs, Colorado destroyed nearly 350 homes and was the most destructive fire on record for the state. The Whitewater-Baldy Complex fire charred nearly 300,000 acres and was the largest on record for New Mexico.

Once the summer season ended, temperatures compared to normal were not in record-setting territory but still above average and precipitation remained below average.

Each season of 2012 had below average precipitation and the year as a whole ranked 15th driest on record. As of January 1 (2013), 61 percent of the contiguous U.S. is experiencing at least moderate drought which, unless there is abundant winter and spring precipitation, could mean another very challenging summer ahead for agriculture in the Heartland.

The record-setting average temperatures in 2012 fit into a long-term pattern of warming temperatures in the U.S.

“We’ve entered a stage now, where [the warming trend] is going to be pretty obvious to the man on the street,” Karl said. “[This year’s warmth] doesn’t mean every season and every year will be this warm, but you’re going to see this with increasing frequency.”

Just as temperatures were warm in the U.S., they were also warm globally. Through November, global temperatures ranked 8th warmest on record in 2012. NCDC will release its year-end report for the globe next week.