Southeast Climate at a Glance - December 2015

Following a mild November, December 2015 was also warm and wet across the region. The entire Southeast experienced above average temperatures and precipitation totals during December. In fact, many states set new temperature records. Specifically, nine states set December records for their statewide average temperature, maximum temperature, and minimum temperature.

Temperature Summary 

December temperatures were much above average with some locations reaching the 70s and 80s. Many weather stations observed record-breaking temperatures throughout the month. Virginia, Kentucky, Tennessee, North Carolina, South Carolina, Georgia, Florida, Alabama, and Mississippi experienced their hottest December on record (Fig. 1). Most of the region was 9 to 14 degrees F above their mean temperature norm, while southern Florida was 6 to 9 degrees F above their mean. The warmest part of December was the 24th through the 27th as maximum temperatures reached the 70s and minimum temperatures remained in the 60s. The coolest part of the month was the 19th and 20th as minimum temperatures fell below 30 degrees F over most of the Southeast. 

Figure 1. Statewide average temperature ranks for the month of December. Source: NOAA/NCEI

Precipitation Summary

Most of the region observed above average precipitation totals by the end of December. In total, eight states (Virginia, Kentucky, North Carolina, South Carolina, Georgia, Alabama, and Arkansas) observed well above average precipitation totals (Fig. 2). Stations in Alabama, Georgia (except the southeastern quadrant), northern South Carolina, North Carolina, south-central Virginia, the Florida Panhandle, and southern Florida recorded precipitation totals 200 to 600 percent of normal. Stations across central and northern Florida and southeastern Georgia recorded precipitation totals 5 to 50 percent of normal. 

Figure 2. Statewide precipitation ranks for the month of December. Source: NOAA/NCEI

Drought and Climate Impacts on Agriculture

There were no drought conditions (class D1 or greater) present during December. 

There were some damaged agriculture reports across the region. Heavy rainfall events caused flooding over southeastern Florida and damaged winter yellow squash, zucchini, and green beans. In Georgia, farmers were unable to harvest a significant amount of their pecan groves due to saturation. Lastly, lack of cold temperatures (specifically between 32 and 45 degrees F) in Georgia reduced the necessary winter dormancy for peach trees and blueberry bushes. This will likely negatively affect the yield in 2016.  

In Summary

A couple contributing factors to the abnormal December climate is the El Nino and Arctic Oscillation. El Nino tends to enhance the subtropical jet stream, which directs storm tracks along the southern states. An El Nino normally causes above normal precipitation totals across the southern states during the winter months. In regards to the temperature, the Arctic Oscillation was positive for the majority of December. This means that the Arctic air is trapped in the polar region. Consequently, arctic air masses remained north while southerly flow directed warm air in the region causing above normal temperature conditions. 

NOAA National Centers for Environmental Information, State of the Climate: National Overview for December 2015, published online January 2016, retrieved on January 13, 2016 from http://www.ncdc.noaa.gov/sotc/national/201512.

Raleigh December Climate Summary

Winter in the southeastern United States is usually mild, but this past December was far from normal. December 2015 ranked as the hottest December on record average maximum, mean, and average minimum temperature for the Raleigh weather station. Across the entire state, almost every station recorded its warmest December on record for mean temperature and a few others recorded their second warmest. Along with warm temperatures, total precipitation was about 3 inches above normal for Raleigh.

Temperature

The mean average temperature was 56.1F, which is 12.7F above normal! December 2015 ranked as the hottest December ever recorded for Raleigh. Raleigh experienced a few cold days, but overall the temperature was much above normal (Fig. 1). The warmest day was Christmas Eve as the temperature topped at 77F. The average maximum temperature was 65.1F, which is 11.6F above normal. The average minimum temperature was 47.1F, which is 13.8F above normal. 

Figure 1. The average mean temperature during December for Raleigh

Precipitation

The first half of December was relatively dry with only a few light rain events around 0.04". The second half of December was active which caused the total precipitation to surpass the normal amount (Fig. 2). Raleigh received 6.07" of rain, which is 3.00" above the norm. Overall, December 2015 ended with the 11th wettest December on record. 

Figure 2. The total precipitation amount during December for Raleigh

Why was it so warm?

There are many natural climate oscillations that have a big impact on our climate. Studies show that the El Nino-Southern Oscillation influences our climate during the winter months. An El Nino enhances the subtropical jet, which directs storms along the southern states. This pattern normally causes above normal precipitation anomalies along the southern states (much like we observed during December). Another climate oscillation that greatly influenced this past December is the Arctic Oscillation (AO). Studies have shown that the AO impacts our wintertime temperatures. A positive AO indicates that the pressure system is strong, which traps the Arctic air in the north. A negative AO means that the pressure system is weaker, which allows the frigid air to move equatorward. Figure 3 shows that the AO was positive for much of December. 

Figure 3. Arctic Oscillation observations and forecasts. Data source: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif 

Additionally, the surface and upper air pattern directed the warm, moist air from the equator up towards the midlatitudes (Fig. 4). Following a record warm autumn, December was far from normal, too. 

Figure 4. Upper air map at 500 mb. Black lines are lines of constant pressure (isobars), dashed red lines are lines of constant temperature (isotherms), and blue flags indicate wind speed and direction in knots. Source: http://www.spc.noaa.gov/cgi-bin-spc/getuadata.pl?MyDate1=151224&Time1=12&MyDate2=&Time2=12&align=V&Levels=500

The remainder of winter

A weather pattern shift occurred in the beginning of January causing Raleigh to experience below normal conditions for both temperature and precipitation thus far. The AO shifted negative, which caused the temperature pattern to be below/around normal. The remainder of January should be below normal for temperature and precipitation. If the storm tracks follow along the southern states and into the Gulf of Mexico, we could see a winter storm. As for February and March, the climate models indicate that the temperature could swing either direction (above or below normal) and the precipitation should be above normal (which is indicative of an El Nino pattern).