News•February 9, 2011

January Was Cooler and Drier Than Average Across the US

In what is unlikely to be a surprise to most Americans who have been shivering and shoveling to an unusual extent so far this winter, new figures released this week show that across the United States, January was much cooler than average. What may come as unexpected news, however, is that it was also a very dry month.

Official national statistics of January temperatures across the lower 48 states were released by the National Climatic Data Center (NCDC), and they confirmed what most people had already felt during the first month of 2011 — it was colder than average. More specifically, it was the coolest January since 1994, with an average monthly temperature of 30°F, two degrees below freezing, and 0.8°F below average. The instrumental weather record the NCDC uses extends back to 1895.

Data from the National Weather Service's analysis of snow depth in the U.S., showing how much snow was on the ground following a January 10-12 snowstorm. Credit: NOAA

The Midwest, Southeast and the Northeast regions all experienced cooler-than-average temperatures during January, and only the three West Coast states — California, Oregon, and Washington

— had warmer than average conditions.

Various factors conspired to make January especially cold, including La Niña, which is a natural climate cycle characterized by cooler than average water temperatures in the eastern equatorial Pacific Ocean. La Niña, like its better-known relative, El Niño, can alter weather patterns around the world.

But La Niña was not the only influence on January’s weather. NCDC also attributes the trend of cooler-than-average temperatures to the behavior of the Pacific/North American circulation, or “PNA”, which concerns fluctuations in the jet stream above the Pacific Ocean and into North America. In a particular phase, the PNA is known to tip the odds in favor of cool temperatures in the south central and southeastern U.S. in particular. Also, especially in early to mid-January, a polar atmospheric circulation known as the Arctic Oscillation helped drive cold air southward, out of northern Canada and the Arctic.

Though the year started off with well over half the country blanketed in snow — midway through January every state other than Florida reported some snow on the ground — last month was actually the 9th driest January on record. Overall there was below-average total liquid precipitation (including the amount of water contained in the snowpack) in much of the country.

Very dry conditions have been plaguing the American Southwest, with New Mexico, Arizona and Nevada posting their driest or second driest January on record.

U.S. Temperature rankings by state for January, 2011. Credit: NCDC.

The U.S. was not the only region of the globe to experience a cooler than average January. A satellite-derived analysis of last month’s global temperatures from the University of Alabama, Huntsville shows that the run of well above average global temperatures seen in 2010 came to an end last month. This is likely due to the influence of La Niña, which increases the odds for cooler than average global temperatures.

Paradoxically, while people in the lower-48 states shivered, parts of the Arctic experienced unusual warmth in early to mid-January. In fact, January 2011 marked the lowest-ever recorded sea ice extent for this time of year, according to the National Snow and Ice Data Center, indicating warm temperatures have taken a toll on the ice cover there.

NCDC isn’t expected to release official global numbers for January until later this month, but there are a few climate trends from around the world that they have already identified.

The flooding that began last September in many parts of the Southern Hemisphere continued into the new year, and January was a particularly bad month for severe floods. In the past month, heavy rains have led to devastating floods in a number of countries:

Following their third wettest year on record (2010), record rainfall continued in parts of eastern Australia in early January, causing severe flooding. Damages are estimated to top $30 billion.
Heavy rains in the first week of January left many regions of the Philippines underwater. During two weeks of floods, the death toll rose to 57 people.
Sri Lanka suffered record high rainfall in the first two weeks of January; over one million people were displaced from their homes during the subsequent floods, and as many as 40 people were killed.
An intense bout of rainfall in Southeast Brazil in early January led to flooding and deadly mudslides. With a death toll of nearly 1,000, the floods are considered the worst natural disaster in Brazil’s history. Floods were also recorded in both Rio de Janeiro and São Paulo.
Serious floods in January were also recorded in Malawi, Malaysia, Mozambique, Saudi Arabia, South Africa, Zambia and Zimbabwe.

Check back next week for an update when official global numbers from January are released by NCDC.

Climate Central's Andrew Freedman contributed to this article.