5:00 PM CDT | August 17, 2018
Right now, conditions in the Pacific Ocean are considered "ENSO-neutral". ENSO stands for El Nino/Southern Oscillation. As NOAA states, "A prominent aspect of our weather and climate is its variability...At times, the year-to-year changes in weather patterns are linked to specific weather, temperature and rainfall patterns occurring throughout the world due to the naturally occurring phenomena known as El Nino and La Nina." El Nino is the warm phase of the Pacific, and La Nina is the cold phase. When conditions represent neither, it is considered neutral. Neutral conditions often coincide with the transition between El Nino and La Nina events. Current indications and recent model guidance is consistent with El Nino conditions developing this fall, likely in October. The majority of the guidance suggests it peaking as a moderate El Nino with an anomaly in the 1.0 to 1.5°C range.
In *most* cases, El Nino brings wetter and cooler weather to our part of the nation. The cooler conditions are often the result of the increased rainfall, not necessarily as a result of frequent Arctic air intrusions. When the pattern is favorable for Arctic air to push southward during El Nino events, we have seen some decent Winter Storms. Unfortunately, it is too early to say at this point if the pattern will favor frequent Arctic air intrusions.
Let's take a look at some recent El Nino events that followed a La Nina event and what resulted that winter for Dallas-Fort Worth. In 2009-10, we saw a moderate to strong El Nino event with a peak anomaly of 1.6°C in December. It was the 7th coldest winter on record for DFW Airport with an average temperature of 42.9°F. It was a very active winter and one of the snowiest on record. A total of 17.1" of wintry precipitation fell that season! This occurred from December through March.
The previous El Nino that followed a La Nina would have been 2006-07. It had a peak Pacific anomaly of .9°C in November and December. That winter did not rank in the top 10 in temperatures or precipitation. Only .3" of wintry precipitation occurred that season from November through April. The next would be the winter of 1976-77. We saw a weak El Nino that peaked with a temperature anomaly of .9°C in November. It was the 8th coldest winter on record with an average temperature of 43.0°F at DFW. From November through January, 10.4" of wintry precipitation fell, which was well above normal. Then we had the winter of 1971-72, which was influenced by a strong El Nino. It was not a top 10 in temperatures or precipitation but did result in 3.7" of wintry precipitation which is a bit above normal.
Out of these four El Nino events, three produced above normal wintry precipitation. Two of these winters ranked in the top 10 coldest on record for Dallas-Fort Worth. The exception would be 2006-07 which featured below normal wintry precipitation. This quick look would suggest that there will be a tendency for a more active winter than usual. Some of the weather models do suggest this possibility, BUT there is at least one or two that shows a pocket of cooler water off the West Coast late this fall and winter. Unfortunately, if this were to happen, it could throw the forecast. This is because it would influence the position of the ridge and make Arctic air less likely to push into Texas. That is a discussion for another time. I just wanted to discuss what we are seeing now and how it compares to past events.