Temperatures over the Lower 48 in 2015 relative to long-term average. (NOAA)

2015 is sure to rank as the warmest year on record for our planet, and much milder than normal weather in the U.S., accentuated by a record smashing December, fits right into the global picture.

[2015 almost certain to be Earth’s warmest year on record by an enormous margin]

NOAA announced today that 2015 finished as the second warmest year for the Lower 48 in records dating back to 1880.  It was a super toasty December that really pushed the year into a historically warm position.

December’s astonishing warmth

Unprecedented warmth torched the eastern United States in 2015’s final month. 29 states had their warmest Decembers on record which elevated the average temperature of the contiguous U.S. to record warm levels. The month ended up six degrees above average, and nearly a degree above the previous record set in 1939.

Average temperatures over the Lower 48 in December relative to long-term average. (NOAA)

In many of the record warm states during December, individual cities obliterated previous records, particularly in the Mid-Atlantic and Northeast. For example:

  • Raleigh broke its record by almost three degrees.
  • Washington, D.C. broke its previous record by almost six degrees.  Its December temperature was warmer than an average November.
  • Philadelphia crushed its old record by almost seven degrees.  Astonishingly, its average low temperature was warmer than its typical December overall (averaging its highs and lows together) temperature.
  • New York City sailed past its old record by about six degrees.
  • Boston exceeded its previous record by more than four degrees.

Literally, hundreds of weather observing stations in the East had their warmest Decembers.  The warmth climaxed on Christmas Eve and Christmas Day, when 70 degree warmth extended as far north as Vermont and the Canadian border, shattering records.

[Records smashed on East Coast’s warmest ever Christmas Eve]

Not only was the warmth unrivaled during December, but so was the amount of precipitation.  It was the wettest December on record, with average precipitation 3.93 inches, 1.58 inches above normal. A deluge that drenched large parts of Missouri and Illinois late in the month, leading to historic Mississippi River flooding, contributed to the surplus.

[The historic Mississippi River flood: Before and after, from space]

December marked the first time on record any month has been both record wet and record warm for the U.S. in 121 years of records.

2015: Second warmest year for the U.S.

The toasty close to 2015 boosted the average annual temperature for the Lower 48 to its second warmest level on record, behind only 2012. Before the record-setting December, 2015 had only ranked as fifth warmest.

The year began with with a warm pattern in the western U.S., but bitter cold in the East.  But, by the end of the year, the pattern flipped, with decidedly warmer temperatures relative to average in the Eastern U.S. compared to the West.

Eleven of 2015’s 12 months were warmer than normal, and, averaged over the entire year, every single state was warmer than normal.

The Pacific Northwest and Southeast were particularly warm.  Florida, Washington, Oregon, and Montana all had their warmest years on record.

Ten weather and climate disasters exceeding $1 billion in damages impacted the nation over the course of the year.  An measure tracking  extremes in temperature, precipitation, and tropical storms indicated levels 70 percent above average and the fourth highest on record.

Billion dollar weather disasters in 2015. (NOAA)

The warmth of 2015 fits into the long-term trend of gradually rising temperatures in the Lower 48.  Eight of the top 10 warmest years on record for the Lower 48 have occurred since 1998.

The warmth pumped into the atmosphere by the strong El Nino event, characterized by much warmer than normal sea surface temperatures in the tropical Pacific, certainly gave 2015’s temperatures a boost.   But the push from El Nino was on top of the warming trend most likely related to accumulating greenhouse gases in the atmosphere from human activities. Since 1901, the average surface temperature of the Lower 48 has risen at an average rate of 0.14 degrees per decade.


More from the Capital Weather Gang

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Washington, D.C. obliterates record for warmest December

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