2012 marked the warmest year on record for the United States and was also the second most extreme ever, the US government agency charged with monitoring weather events, said Tuesday.

The hot weather contributed to a record drought which, at its peak, parched 61 percent of the nation, destroyed crops worth billions and slowed shipping on the mighty Mississippi River as water levels reached historic lows.

Those dry conditions helped spark massive wildfires that charred 9.2 million acres, the third highest annual figure on record, the National Oceanic and Atmospheric Administration (NOAA) said.

The nation suffered through 11 weather disasters that caused $1 billion in damage or more, including hurricanes Sandy and Isaac and deadly tornado outbreaks in the Great Plains, Texas and the Ohio Valley.

Sandy proved the most destructive as it made landfall near New York, killing 131 people, knocking out power to eight million people and destroying tens of thousands of homes and businesses.

US President Barack Obama signed a bill Sunday approving $9.7 billion in emergency disaster aid for victims of the superstorm, which is just a small wedge of the comprehensive $60.4 billion package sought by the White House.

2012 was the third year in a row with 19 named tropical storms, 10 of which packed hurricane strength. One was a major hurricane.

Some relief came from one of the slowest tornado seasons in decades with just 878 confirmed twisters and 58 reports still pending review.

However, it was still a deadly and destructive year: three tornado outbreaks caused at least $1 billion in damage and there were 68 tornado-related fatalities.

Every one of the 48 states in the continental United States had an above-average annual temperature in 2012 and 19 of those broke records.

The average temperature for 2012 was 55.3 F (12.9 C), which is 3.2 F above the 20th century average, and 1.0 F above 1998, the previous warmest year.

The warm temperatures meant that the winter season "was nearly non-existent for much of the eastern half of the nation," NOAA said.

The December 2011 to February 2012 period was marked by near-record warmth across the US-Canadian border, the Midwest, Mid-Atlantic, and the Northeast.

Many locations had near-record low snowfall totals for the winter, which left soil parched and contributed to the drought.

"Early spring brought much of the same, when the contiguous US had its warmest March on record, with a monthly temperature 8.6�F above average," NOAA said.

July also broke records with an average temperature of 76.9 F (24.9 C), which was 3.6 F above average and the hottest month ever observed for the contiguous United States.

A sweltering June and August contributed to a summer average temperature of 73.8 F (23.2 C), which made 2012 the second hottest summer on record by only hundredths of a degree.

Almost 100 million people -- nearly a third of the nation -- sweated through 10 or more days of summer temperatures greater than 100�F (37.8 C)

The nationally-averaged precipitation total of 26.57 inches (67.5 centimeters) was 2.57 inches (6.5 centimeters) below average and the 15th driest year since record-keeping began in 1895.

Yet Florida had its wettest summer on record, thanks to the tropical storms, and Minnesota had record flooding after a summer storm dumped eight inches (20 centimeters) of rain on Duluth in a 24-hour period.

This was also the driest year for the nation since 1988, when 25.25 inches (64.1 centimeters) of precipitation were observed.

The US Climate Extremes Index -- which evaluates extremes in temperature and precipitation along with tropical storms that make landfall -- was nearly twice the average value and second only to 1998.