Wednesday, December 28, 2011

Arctic Blast Expected Next Week

This winter has been a mild one for much of the eastern half of the country.  In fact it has been well above normal in areas traditionally cold.  The mean temperature in South Carolina has been generally from 4 to 5 degrees F above normal for December.

The mean temperature and anomalies for December through the 26th.  Image credit: NOAA/CPC.
The outlook for this winter was for warmer than normal temperatures in South Carolina and drier than normal conditions.  This was primarily because of the La Nina that formed in the Pacific tropical region.  We had a La Nina last year and it was colder than normal.  The difference has been the Arctic Oscillation.  Last year it was in a negative phase which allowed much of the cold Arctic air to move south.  This year it has been in a positive phase which has kept the bitter cold air bottled up in the polar regions.

Now there is about the be a sharp change in the weather pattern albeit brief.  The upper-level jet stream will dip far to the south early next week.  This will allow an arctic air mass to plunge south into the nation's mid-section over the weekend.  The weather will be fine for South Carolina through New Years Day.  However, a strong cold front will pass through the state Sunday night.

It is expected to be a dry frontal passage.  However, windy conditions are expected for Monday and Tuesday as the cold air rushes into the Midlands.  High temperatures will be in the low to mid 40s on Tuesday and low temperatures will be in the low to mid 20s by Wednesday morning.  Some of the low-lying areas may see temperatures in the upper teens.

Forecast of surface temperatures valid 7 a.m. Tuesday, January, 3,2012.  Image credit: WSI.
This will be the coldest outbreak for South Carolina so far this season.  Now is the time to prepare for its arrival.  Pets and plants will need protection from the cold weather.  Pets have not had enough time to acclimate to such conditions.  In addition there is likely to be a considerable wind chill Monday night.  Wind chill temperatures could be in the teens Tuesday morning.

The European Centre for Medium-Range Weather Forecasts computer model began suggesting this two days ago.  Today all of the computer models are essentially in agreement with a few minor differences.  Thus, confidence is moderate to high in the forecast.  There will likely be refinements in the forecast at this time range, but the overall forecast seems clear.
This cold snap will be brief.  A warming trend will begin on Wednesday, January 4, 2012, and will continue through the next weekend.  The unseasonably mild winter weather will be back for the weekend.