A Winter North Atlantic Oscillation Predictor in the North Pacific ONLY during El Nino Events.

Here is a bit of climate research from the summer of 2004. It ONLY works during El Nino years defined with the 1971-2000 base period Oceanic Nino Index. From here we look to the North Pacific Sea Level Pressure status throughout October to be deterministic of the December-March North Atlantic Oscillation (NAO). October SLP's below 1013-hPa indicate a higher likelihood of a -NAO, while SLP's above indicate a higher likelihood of a +NAO or Neutral NAO.

Now, the problem for the winter 2014-2015 is we don't know if we will have an official El Nino event as defined by the ONI (5 trimonthly periods of 0.5C or higher in Nino Region 3.4). Some models are predicting an El Nino, some are not. Right now, according to climatology I have used, the only type of +ENSO events that really can occur is a weak event, with a very outside chance of moderate.

The Experimental Winter DJF 2014-15 NAO Forecast using Zonal Wind indicators from May & September

This is a NAO forecast based on research done in 2011, whereby certain zonal wind anomalies in the Northern Hemisphere during May and September are used as predictors. It has worked decent during 2 of 3 forecasts from the winters of 2011-12 & 2012-2013, but busted rather harsh during the Winter of 2013-2014.

Figure 1. Tropical Northern Hemisphere 500mb Loading Pattern in +Mode (NOAA/CPC)

In my attempt to try to figure out why, I remembered the extreme North Pacific regime and Tropical Northern Hemisphere (TNH) (Figure 1) blocking in the Winter 2013-2014 was dominant to the point where I believe it may have affected some way the expected Atlantic DJF blocking outcome (NAO). I noticed the 2 times the model failed quite badly was during periods of extremely positive TNH values, as a matter of fact the winters of 2008-2009 and 2013-2014 had the highest DJF TNH values since 1948. This meant a very strong Hudson Bay Low anomaly over Canada and above normal 500-hPa heights from the Gulf of Alaska to just of the coast of California. Out of all the winters with a TNH of +1 S.D., 4 out of 6 had inaccuracies, which was the largest cluster of inaccuracy found in the data. The model's R^2 has dropped from 0.79 to 0.69 due to the 2013-14 forecast failure, but still describes 69% of the NAO.

NAO Forecast Graphic

The Winter of 2014-2015 could very much be driven by North Pacific dominate variables, although that is not a guarantee. If that is the case, this forecast could be offset by a +TNH dominant winter, so take it as an "Experimental" tool not a definite. The NAO is essentially being forecasted as neutral with a value of -0.13 but with error -0.13 +/- 0.2 or -0.33 to 0.07.