What Drove Tropical and North Pacific and North America Climate Anomalies in 2014/15 Winter?

From October 2014 to March 2015, the Niño3.4 index, referred to as sea surface temperature (SST) anomaly averaged over 170W-120W, 5S-5N, was in a 0.5C to 0.9C range. At the same time, except for the February 2015, the southern oscillation index (SOI), defined as the standardized surface pressure difference between Tahiti and Darwin (former minus later), was in a range of -0.6 to -0.9. The values of the both indices exceeded the thresholds for a weak El Niño conditions (Trenberth 1998). However, the atmospheric anomalies over the same time did not reflect typical ENSO like conditions, leading to the question why atmospheric circulation did not show a response typical to what is generally observed during El Niño conditions?