Long Range Outlook: January 1, 2014

ECMWF (left), GFS (center) and CMC Long Range 500mb anomaly forecast

Long Range Discussion
January 1 2014

Multi-model guidance above for the 8-10 day period shown is in average agreement, with highest disagreement area over northern Canada into Greenland, leading to additional disagreement over the Northeast United States. Model confusion revolves around whether to allow development of strong low pressure over Greenland, which would then help chances for ridging out towards the Northeast and East Coast. ECMWF and GFS are in the "best" agreement of the three model suite, with the ECMWF centering the anomalous low pressure west of Greenland and the GFS strengthening said low pressure system and placing it south and east of Greenland. The difference in location will affect the large-scale weather pattern, with a more compact solution with that upper-latitude low pressure system as exhibited by the ECMWF leading to stronger ridging along the East Coast. On the other hand, if the system is to be placed east of Greenland, the low pressure would be elongated from the Bering Sea out to the waters east of that land mass, and that would temper ridging prospects in the East US.

Model guidance is in good agreement on ridging keeping a chokehold on the Arctic Circle, which will prohibit reformation of the polar vortex across that area, and thus will keep the risk for cold weather across lower latitudes rather high. All modeling systems are also in agreement on ridging appearing over the southern Gulf of Alaska and into the north central Pacific, and we also find a consensus among the guidance with deep low pressure over the Bering Sea into Alaska. Now, for the long range that we are watching over for this time period (8-10 days out), this means we will be seeing a pattern that will most likely keep out extreme cold weather like we will see to kick off the upcoming workweek. In the long-long range, this somewhat-anti-cold pattern will flip over.

This map from Michael Ventrice shows 200 hPa velocity potential anomalies over a time-longitude graph. Blues and dashed ovals indicate the presence of enhanced convection (and thus a Madden-Julian Oscillation / MJO wave), while solid ovals and warmer colors signify a suppressed MJO wave. Taking a look at past, present and future conditions, we see how the MJO wave has been progressing across the Indian Ocean and towards the central Pacific for some time, oscillating through the various phases of the MJO. Some dynamical models were giving off a false "dead MJO" signal, where the guidance indicated the MJO was too weak to track. In reality, this was another body of enhanced convection firing over South America. This dual-placement of tropical convection is referred to as a "Wave 2" pattern, due to the two waves of active convection. In reality, the MJO signal was always oscillating around the phase space, as the progression of the MJO wave in the graph above shows. Now, as we look ahead, the GFS projects the MJO wave to continue pushing east, to be centered at the ~170E longitude mark around January 10th. This is a classic forecast of the MJO pushing through Phase 6 (centered around 160E), and Phase 7 (centered around 180). Model guidance should see an intensification of either the zonal flow across the US or ridging on the East Coast, as ridging in the US is common in a January Phase 6 event. A January Phase 7 event results in significant ridging in the West that will then transition us into the mid/late January cold blast that I began discussing earlier today.

Teleconnection forecasts from the ESRL agency appear to be handling the upcoming pattern decently well, with a few spots that may be refined in future forecasts. The Pacific North American (PNA) index is projected to be deeply negative in the short term, meaning deep troughing across the West US. I expect we see this deep negative forecast moderate to more neutral territory, as the MJO does not really support such a huge -PNA event. I find it more likely that this strong troughing will be more displaced to the east, as ensemble guidance supports. From then on, we see another negative PNA spell before spiking positive. I have good confidence in that +PNA spike in the long range, with some decent confidence in relatively neutral PNA values in the medium/long range. For the North Atlantic Oscillation (NAO), the index is projected to remain positive throughout the forecast period. I figure we will see a slight negative trend in the long range +NAO values, as an MJO Phase 7 supports more negative NAO values. However, other than that, I feel confident in the prolonged +NAO forecast. The West Pacific Oscillation should stay positive for much of the forecast period before a reduction to neutral or negative territory comes about in the long range in response to the transitioning MJO. I disagree with this WPO forecast. The East Pacific Oscillation (EPO) looks to me like it will be more negative than positive. The medium and long range EPO is projected to be positive, but ensemble guidance disagrees and places the EPO at a more neutral or slightly negative stance. I expect we will see some correction in that direction for future teleconnection forecasts.

To summarize, I anticipate some warmer weather arriving in the wake of brutal cold for the second week of January, before we see a trend towards colder conditions in time for the end of that second week and into the third week of January.

Andrew