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Will La Niña or Statistics Determine What Happens This Winter?
 
Temperatures were below average during much of the summer (June through August) at Little Rock (Pulaski County). The cool trend continued to begin September, 2017.
In the picture: Temperatures were below average during much of the summer (June through August) at Little Rock (Pulaski County). The cool trend continued to begin September, 2017.
 

While summer (June through August) often brings oppressive heat to Arkansas, this was seldom the case in 2017. The average temperature (77.7°F) was about a degree on the cool side, making it the 25th coolest summer on record (dating back to 1895). It would make sense that the winter ahead (December, 2017 through February, 2018) will be cold, right? Maybe.

Looking back at the ten coolest summers across the state, the winters that followed were cold sometimes and mild other times. In 1976, the 4th coolest summer occurred (tied with 1903). The winter of 1976/1977 was brutal, and the 9th coldest on record. Meanwhile, the 8th and 9th coolest summers were 2004 and 1920. The following winters were the 15th and 11th warmest respectively.

 

Top 10 Cool Summers and Following Winters in Arkansas
Site Summer Avg Temp +/- Winter Avg Temp +/-
1961 75.7° -3.0° 41.3° 0.0°
1992 75.7° -3.0° 40.9° -0.4°
1967 75.9° -2.8° 39.2° -2.1°
1903 76.0° -2.7° 39.7° -1.6°
1976 76.0° -2.7° 36.7° -4.6°
1915 76.1° -2.6° 42.7° +1.4°
1950 76.2° -2.5° 40.6° -0.7°
2004 76.3° -2.4° 44.6° +3.3°
1920 76.5° -2.2° 44.8° +3.5°
1974 76.6° -2.1° 42.3° +1.0°

 

If you are looking for a cold winter, there is good news. The last two winters (2015/2016 and 2016/2017) bordered on toasty, and both are on the Top 10 mild list. If we were to have a similar winter this time around, it would be unprecedented. More specifically, there have not been three straight winters in Arkansas with temperatures at least three degrees above normal. Aside from three in a row, one such winter is rare, and has happened only 17 of 122 times.

Now, there have been sizable streaks of warmer than average winters by at least 0.5 degree. One streak went seven years from 1920/1921 to 1926/1927. There was a six year streak from 1929/1930 to 1934/1935. Records show another five year streak and two four year streaks. The most recent streak lasted from 2004/2005 to 2008/2009. But streaks such as these are fleeting, with most streaks lasting two to three years before the sign changes (from a mild plus to a cold minus). We are in the midst of a two year mild streak, and it may be time for a change.

 

Three in a Row

Arkansas has come close to having three consecutive winters with temperatures at least three degrees above average. In the winters of 1920/1921 to 1922/1923, the three degree threshold was met twice, but the third year was only two degrees warmer than normal. It was a similar situation in the winters of 1997/1998 to 1999/2000. On the flip side, the winters of 1976/1977 to 1978/1979 featured readings more than four degrees subpar! All three winters are on the top 10 cold list.

 

Neutral to weak La Niña conditions are expected this winter into the first half of 2018. The data is courtesy of the International Research Institute for Climate and Society/Columbia University.
In the picture: Neutral to weak La Niña conditions are expected this winter into the first half of 2018. The data is courtesy of the International Research Institute for Climate and Society/Columbia University.
 

From a model perspective, this winter will be somewhat difficult to forecast. One of the most reliable long-range predictors deals with monitoring water temperatures along the equator in the Pacific Ocean. If the water cools, we trend toward La Niña conditions. If warming occurs, we are headed for El Niño. Both variables have a say in how the weather behaves across the country, especially when they become dominant. This winter, while the pendulum will sway toward La Niña, it won't be much of a swing (minor/weak). This will make the forecast more challenging. It will also open the door for less reliable variables or wildcards to factor into the equation.

 

A Textbook Situation

When La Niña becomes the primary variable in winter, the expected outcome is warmer/drier than usual conditions in portions of the southern United States, with colder/wetter than average weather in parts of the north. When El Niño is in charge, the opposite is often anticipated.

 

The Arctic Oscillation (AO) index was strongly negative for much of the winter of 2010/2011.
In the picture: The Arctic Oscillation (AO) index was strongly negative for much of the winter of 2010/2011.
 

One such wildcard to keep an eye on is the Arctic Oscillation (AO). The AO is all about pressure differences between the North Pole and the mid-latitudes (where we live). The AO is negative when the pressure to the north increases, with lower than normal pressure closer to home. In winter, this causes westerlies in Canada to slow down, and cold air is allowed to spill into the United States on a more regular basis. A negative AO was noted during the winter of 2010/2011, with cold temperatures and snow piling up in Arkansas.

 

Is It a Sign?

On the morning of October 28th, Little Rock (Pulaski County) had an early freeze (low temperature of 31 degrees). This was more than two weeks premature of a typical first freeze (November 14th). Locally, it was the first freeze in October since 1993, and the earliest freeze since October 20th, 1989. It froze again the next morning, with a reading of 28 degrees. This was the second coldest October temperature on record (which was 27 degrees on the 30th of 1917), and the first time with multiple October freezes since 1957.

 

The North American Multi-Model Ensemble (NMME) is showing above average temperatures this winter over much of the country, especially east of the Rockies.
In the picture: The North American Multi-Model Ensemble (NMME) is showing above average temperatures this winter over much of the country, especially east of the Rockies.
 

Currently, most long range models are calling for a warmer than average winter across much of the country, including Arkansas. If the models are right, we may be headed for uncharted territory locally. As mentioned, three consecutive very mild winters would be a first. Statistically speaking, and going by the numbers, what the models say just doesn't add up.