Wednesday, October 17, 2012

Cold Outbreak Rounding Out Next 10 Days; Cool Halloween Ahead?

The 12z ECMWF is slamming down on the nation with an absolutely brutal cold snap coming to the northern Plains an eventually the central and eastern parts of the nation in the next 10 days.

Above are two images dealing with the 850mb level, commonly used to identify areas of warm and cold air. The ECWMF is taking a major storm in Canada and having it sweep brutally cold sir south into the US. The bottom image is 850mb temperature anomalies, of which are bottoming out as low as 19 degrees below normal!

Many locations will be at risk for some flakes flying. If there will be any accumulation remains to be determined, but this cold snap could lead the way for a bang to start November in the East- and possibly a very chilly Halloween.


Warming Temperatures Accompany Next Week

This temperature graph from the GFS Ensembles is showing a very defined warm up over the Plains and Midwest, among other regions, going into the beginning of the upcoming work week. Let's take a look into what this is all about.

This is a picture of the average temperature anomalies that the 12z GFS Ensembles are showing for Monday, October 22nd. The ensembles are displaying temperature anomalies as much as 12 to 15 degrees above normal- quite a feat for late fall. This warm up comes as a deep negative PNA signature takes over. When you get that cold over western Canada and the Northwest US, such a stormy and cold pattern in those regions commonly leads to a warm up in the central and eastern regions of the States.

This warm up looks to be fairly progressive, with positive temperature anomalies lasting only a few days before another big release of cold air hits the nation.

It looks like the weekend and beginning of the upcoming work week may allow the heavy jackets to go into a short hibernation!


Northern Hemisphere Snow Cover Above Normal

Latest indications from Florida State University (of all places to track snow) are showing the first above-normal marking of North Hemisphere snow cover in months.

The top graphic is the 7 day snow cover change over the northern Hemisphere, with the bottom image depicting a graph of snow cover anomalies over the same region. It appears a recent burst of snow over Canada and Russia is contributing to this above normal marking.

I expect the Canadian snowfall to diminish over the next week or two, as a massive ridge covers most of the nation, thereby reducing chances for sustained snow cover in the region. However, the continuous building of the Siberian snowpack tells me that snow will likely return for Canada this winter, as well as much of the Eastern US.

Expect my new thoughts on this winter to come out late October-early November.


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.