Sunday, January 1, 2012

Winter Weather Outlook Update

The Climate Prediction Center (CPC) issued the outlook for the winter 2011-2012 back in October and issued an update at the beginning of December.  The winter months are considered to be December, January, and February, because these are the three coldest months of the year.  Climate oscillations like the El Nino/La Nina oscillation tend to make the forecasting of the winter season a little easier.  The wild card is usually the Arctic Oscillation.

This year the forecast looked like this:

Map shows U.S. areas predicted to have well above (red) or well below (blue) normal winter temperatures in 2011-2012.  Image credit NOAA/CPC.

Map shows U.S. areas predicted to have well above (green) or well below (tan) normal winter precipitation in 2011-2012.  Image credit: NOAA/CPC.
The outlook for South Carolina was for the winter to be warmer than normal and drier than normal.  So far the forecast has been on track.  The preliminary data indicates that December 2011 was the 14th warmest and 10th driest on record for Columbia, South Carolina.  Mean temperatures across the U.S. looked like this in December:

Mean temperatures across the U.S. from December 1-30, 2011.  Image credit: NOAA/CPC.
An arctic blast it now pushing into the eastern part of the country and will bring colder than normal temperatures for several days.  This will be the coldest outbreak so far this season.  However, it will be short-lived.

The weather pattern will revert back by next weekend and temperatures will once again be above normal for much of the country.  In fact, January is still forecast to be above normal for much of the country.
Temperature Outlook for January 2012.  Image Credit: NOAA/CPC.
The winter of 2009-2010 was an El Nino year and the winter in South Carolina was much colder than normal.  In fact it was the 4th coldest for Columbia and the 10th coldest for South Carolina.  The next winter (2010-2011) was a La Nina year and it was a strong La Nina.  Yet, it was colder than normal.  Now in the winter of 2011-2012 we have a moderate La Nina and are seeing unseasonably warm weather.


As I mentioned the wild card is the Arctic Oscillation (AO) which has been in a negative phase the past two winters.  In fact two winters ago it was in the most negative phase in years.  This year the Arctic Oscillation has been in the positive phase.  You can see how the two phases affect temperature in the following figure:

Image credit NOAA/CPC.
Note that the different phases changes the placement of above and below normal temperatures.  It is still cold, but the difference is a matter of degrees.

Thus, it appears that the forecast will remain on track.  This winter will likely be warmer and drier than normal for much of South Carolina.  There will be cold outbreaks, but they are likely to be brief.  The more disconcerting forecast is the one for drier than normal.  This may worsen the drought conditions for the spring planting season.  More on that in a later post.