Wednesday, October 17, 2012

Long Range Lookout: Pattern About To Get Dicey

This is the October 17, 2012 edition of Long Range Lookout.

This weather pattern is about to get a whole lot... warmer. Yes, warmer. Above, you can see the 500mb height anomalies on the left, and the GFS Ensemble 'spaghetti' forecast on the right for approximately 6 days away.

The right image is composed of 500mb height forecasts from each member of the GFS Ensembles. When you combine them into one image like the one seen above, the result is a very messy picture (especially in the long range). These twisting, turning lines are what gives the right image the nickname 'spaghetti model' forecast. On the left is the 500mb height anomalies from the ensembles on the right. The 500mb layer is considered the best to look for high and low pressure systems. Blue areas are stormy areas, and red spots are composed of high pressure anomalies. The darker each color is, the stronger its respective apparatus is.

This forecast is showing a strong high pressure stretching across the heavy majority of Canada, including near Greenland, the focus point of the North Atlantic Oscillation (NAO). When you get a ridge like this near Greenland, a negative NAO develops, which can bring cold and snow to the East US in the wintertime. However, check out that deep blue area over the northeast Pacific and western US. That is a very strong negative PNA pattern. In a negative PNA, a deep disturbance locks up the West Coast, and a ridge of high pressure develops in the East US in response. This, in turn, hampers cold and snow efforts to reach the US.

So, over the next week or two, expect a warm up to enter the playing field. This warm up looks to be short-lived before a big cool down enters the States, but that will be on a separate post.

Remember, you can catch Long Range Lookout every Wednesday, here on The Weather Centre.


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