Friday, March 1, 2013

A Change In The March 2013 Outlook

The Climate Prediction Center (CPC) issues outlooks for the next month in the middle of the current month.  They will often issue an updated outlook near the last day of the current month.  Usually these projections do not vary much, but this month saw a substantial revision.

Computer models designed to forecast daily weather are run out to 15 days, four times each day.  Most are familiar with the 7-day forecast.  The CPC also issues 8-14 day outlooks for the second week of the forecast in additions to the monthly and seasonal outlooks that they make each month.

Beginning with the 8-14 day temperature outlook on February 21 and the one issued on February 28, it seems that the first half of March would be colder than normal for South Carolina as seen in the outlooks below.

The 8-14 day temperature outlooks.  The first one made February 21 and the second one (right) made February 28.  Click on the image for a larger view.  Image Credit: NOAA/CPC.

The reason for this projection is that the Arctic Oscillation (AO) has been in a negative phase with the forecast for it to become strongly negative next week.  This usually produces a cold outbreak for parts of the U.S.  Last year the AO was strongly positive and the U.S. saw the warmest March on record.

The initial outlook for March 2013 made in mid-February was for warmer than normal conditions over much of the eastern half of the country.  The persistence of the negative phase AO has changed the outlook to one where it could go either way.  However, the areas forecast to be below normal were not changed much.

The temperature outlook for March 2013.  The left one was made on February 21 while the right one was made on February 28.  Click on the image for a larger view.  Image Credit: NOAA/CPC.

Thus, South Carolina is likely to see colder than normal temperatures for the first half of March.  The month is a transition month from winter to summer, thus you expect a significant warming during March.  However, this year the warming in the latter half of the month may not completely overcome the cold conditions of the first half.  It is prudent to expect that the latter half of the month will be warmer than normal, but the month as a whole will be near normal or slightly warmer than normal.

February proved to be a very wet month for South Carolina.  What does the outlook say about precipitation?  Originally the outlook was for it to be drier than normal, but the new outlook projects equal chances of dry or wet.  More than likely it will be near normal.

The precipitation outlook for March 2013 made February 28.  Click on the image for a larger view.  Image Credit: NOAA/CPC.

This would be good news for gardeners and farmers.  Near normal rainfall will help keep the moist conditions from February and make it better for planting in the spring.  We are still in a drought, but it has eased.  It is the ground water that will benefit from additional rains.