Saturday, September 20, 2014

JAMSTEC Model Predicting Harsh Winter Ahead

A popular weather model, the JAMSTEC climate model, is forecasting a harsh winter ahead... but will it verify?

The image above shows the December-January-February temperature anomaly forecast for the winter of 2014-2015, with the forecast made in August 2014. This forecast is made up of 27 ensemble members, which can enhance its credibility, so long as the forecast is within reason.

In this image, we can see strong below-normal temperature anomalies across nearly the entire United States. Canada and Alaska look to see above to well-above normal temperature anomalies, with the anomalies maximized over the far northern reaches of the country. Last winter, the core of the cold was displaced in the north-central US, but if this model is correct, it would be shifted into the Southern Plains.

On the precipitation side, the JAMSTEC model is forecasting a swath of above-normal anomalies to affect the Southeast US, even stretching west into the Texas/New Mexico region. These wet conditions look to extend up the East Coast, almost in typical El Nino fashion. The Pacific Northwest would see a rather dry winter if this solution were to verify, while the Southwest would see slightly below-normal to average precipitation anomalies.

Even though this model certainly is painting an ominous picture, is it a realistic one?

The graphic above once again shows an outlook for the December-January-February period, but now depicts sea surface temperature (SST) anomalies . In this image, I can identify two areas of concern, as far the forecast potentially not verifying.

First off, we see a moderate to borderline-strong El Nino evolving in the Pacific. SST anomalies of 1.2 to 1.5 degrees Celsius above normal might be a bit too strong for this winter, as I'm currently expecting only a weak to possibly-moderate El Nino. It would be quite a stretch for a strong El Nino to hit this winter.

Second, we see a pool of deep negative SST anomalies in the waters just south and west of Greenland, while well above-normal anomalies flourish on either side of the land mass just north of the cold pool. There isn't as much reasoning behind this one as there is a gut feeling; the alignment of SST anomalies looks odd to me, and I'm not so sure I would put stock in this forecast.

To summarize, the JAMSTEC model is indeed forecasting a very ominous winter to once again hit the United States. However, concerns with the sea surface temperature anomaly forecast for the coming winter could mean the forecast may be flawed.