2015-2016 Winter outlook

El Niño 

The current El Niño is on track to be one of the largest on record (since 1950). This past week's sea surface temperature (SST) anomalies (figure 1) were much above normal with some peaking at 3°C above normal. Although these values are unprecedented, it is not indicative of the events strength. The Climate Prediction Center compares historical El Niño episodes based off of their 3-month SST anomaly mean. The latest Oceanic Niño Index was a 3-month mean over August, September, and October. For this current episode, it was 1.7°C above normal. For comparison, the 1997/1998 El Niño (strongest on record) was 2.0°C above the norm.

FIG 1. Sea Surface Temperatures over the equatorial pacific. source: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstweek_c.gif

Every El Niño episode is slightly different. They reach peak intensity at different times and cause various deviations from climatic norms. With that said, the current El Niño has the potential to surpass the 1997/1998 event. Most climate models are in agreement that this episode will peak during the winter and transition to neutral conditions in the spring/summer of 2016.

Southeast Winter Outlook

So, what does this mean for North Carolina? Normally, an El Niño enhances the subtropical jet stream causing storms to track along the southern states of the US. As a consequence, above average precipitation is expected across the Southeast and North Carolina (figure 2).

FIG 2. Climate Prediction Center 3-month precipitation outlook. source: http://www.cpc.ncep.noaa.gov/products/predictions/long_range/lead01/off01_prcp.gif

 As for temperature, that's a little bit more tricky. Sometimes an El Niño can cause above average temperature, while other episodes cause below normal. This winter season was no exception of a tricky outlook. Most of North Carolina could experience either above or below normal temperatures, while the northern tier will likely experience above normal temperatures within the next three months (figure 3).

FIG 3. Climate Prediction Center 3-month temperature outlook. source: http://www.cpc.ncep.noaa.gov/products/predictions/long_range/lead01/off01_temp.gif

My Take:

This El Niño is rivaling the 1997/1998 El Niño in strength. With that said, 1998 was one of the warmest years on record globally and 2015 is on track to be the warmest year on record. I expect December to be above average for both temperature and precipitation. Going into 2016, it is a bit more difficult to say what the temperature deviation will be. As many of you may remember the past two winters, the Arctic Oscillation (AO) plays a strong role for our temperatures. The AO is also difficult to predict well in advance (it switches phases in weeks or sometimes days). If the AO weakens, we will expect to have cold temperatures in our area like the past two winters. Also, because El Niño causes storms to track along the southern states, if the temperatures are in place, we could see a storm or two. However, I do not expect this winter to receive above normal snowfall. For most of the winter, I believe it will be above normal for temperature and precipitation.