Tuesday, April 10, 2012

Record March for the U.S.

March 2010 in Columbia, SC.  Image Credit: Climate Central.
Those of us in central South Carolina already know that this past March was the warmest on record.  I outlined the records in a previous post.  The graphic to the left covers the period since 1948.  The year of 1974 was the warmest during this time.  However, the records do extend back to 1888 and 1945 was the previous record.

The record warmth was not confined to central South Carolina.  Much of the central and eastern U.S. were part of this record breaking event.  March is usually a transitional month with weather systems progressing across the country producing a wide variety of weather conditions.

Image Credit: NOAA/NCDC.
However, this year was a year characterized by a ridge of high pressure in the East and a trough of low pressure in the West.  The chart to the left shows the mean 500 mb (about 18,000 feet in the atmosphere) heights and the height anomalies for the month.  The blue areas show where the heights were lower than normal and are related to the persistent troughs of low pressure.  The red areas correspond to above normal heights and are related to the areas of higher pressure.  This caused the jet stream to frequently dip far to the south along the West coast and then retreat north into Canada.

Image Credit: Climate Central.
This resulted in the record warmth experienced over much of the country.  It was the warmest March on record for the 48 contiguous states dating back to 1895.  March 2012 beat the previous record set in 1910 by .5 degrees.  It was 7 degrees above normal.

The heaviest rainfall was confined primarily to the area from east Texas over to the Tennessee River Valley and northward into the Northeast.  The Pacific Northwest also saw considerable precipitation with heavy snows in the mountains.

Image Credit: NOAA/NCDC.

More than half the country saw record warmth as the average temperature exceeded previous records (27 out of 48 states).  The average for the Carolinas was only the second warmest even though it was the warmest for Columbia.  An additional 13 states were much above normal meaning that the average temperature for the states was in the top tenth percentile of weather records.

So what is going on?  Our climate is warming.  This was not a case of just climate variability, it was part of a trend.  Note in the graph below the percent of areas experiencing very warm temperatures versus the percent of very cold.  The very warm areas refer to divisional areas experiencing temperatures in the top tenth percentile while the very cold areas are experiencing temperatures in the lowest tenth percentile.  The data comes from the National Climatic Data Center and goes back to 1895.

The trend for March has been for very warm temperatures to greatly exceed very cold temperatures since the 1970s.  The ratio has actually in increased recently.  This corresponds to the warming that began nationwide about the same time.  Even in the two cold winters proceeding the current one, the ratio of very warm areas exceeded very cold areas.

The percent of areas that were very warm vs very cold in the month of March.  Image Credit: NOAA/NCDC.  Click on the image for a larger view.
There is more to this story than just the climate is warming.  New research is revealing how the warming is changing and affecting weather patterns.  This will be the topic of a future post.