Tuesday, May 27, 2014

What Are The Models Saying This Winter? - CMC1 Model

This is a continuation of this series of posts, where we are analyzing long range climate model projections for the beginning of the winter of 2014-2015. This post will feature the CMC1 model.

The temperature forecast from the CMC1 model, valid for December 2014, shows a very chilly winter for many in this country. This model suggests we will see an abundance of warm air overspreading Alaska and the west coast of North America. This is likely the result of high pressure, which then forces mid-level troughing to the east. This mid-level troughing, which will be discussed more later in this post, results in below normal temperature anomalies over the Central and East US, extending as far north as upper Canada. If you follow the weather closely, you may recognize this pattern as a positive Pacific-North American (PNA) index pattern. Like last winter, the Pacific pattern looks to have a grip on the downstream weather here in the US, resulting in a cold start to the winter.

The precipitation forecast from the CMC1 model shows a pattern almost identical to a traditional El Nino winter precipitation pattern. We first see anomalously wet conditions along the West Coast, a telltale El Nino signal due to the subtropical jet stream's natural enhancement due to the aforementioned El Nino. This enhanced subtropical jet stream then leads to more storm systems hitting the West Coast, and then more precipitation. We then see significantly below normal precipitation across the Central US, hitting the Ohio Valley the hardest. Once again, this is an El Nino signature. The El Nino is evident yet again in the CMC1 model's forecast for a very wet start to winter on the East Coast. This all strikes me as odd, since the temperature forecast does not reflect an El Nino temperature pattern, but given how this past winter went, you really have to expect the unexpected.

Lastly, we see the forecast of z200 anomalies for December 2014 from the CMC1 model. We're going to focus on the contour lines over the northern Hemisphere. In this forecast, we see the contour lines arching northward over the west coast of North America, signifying ridging/high pressure in that area. We discussed the likely presence of high pressure along the west coast earlier in the temperature forecast, and now we are seeing that theory come to fruition. We then see the contour lines plummet south over the Central US, which is how we got that cold December forecast at the top of this post. Oddly enough, we then see ridging in the Southeast US, which would typically divert storm systems north through the Ohio Valley. However, the precipitation forecast for the Ohio Valley is very dry, as shown above. This is likely the long range model up to its antics, which means confidence is similarly low.

Additional models will be discussed in coming days.