Hurricane's Blog: Let's Talk About Cold (Now That It's Getting Warmer) - NBC 10 Philadelphia

Hurricane's Blog: Let's Talk About Cold (Now That It's Getting Warmer)

The warm weather we're experiencing is about to change



    Hurricane's Blog: Let's Talk About Cold (Now That It's Getting Warmer)
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    We have quite a warm 7-day forecast, considering we’re in January. A day or two could even reach 60+ degrees this weekend. But at the end of the 7-day, there will be major changes coming.

    I’ve been saying for days that Arctic air is not that far away, and all it will take is a slight change in the weather pattern to get a LOT colder around here. There are now signs of that change.

    Take a look at the map for this weekend:

    Look at it as a kind of map of pressures close to 20,000 feet up. It’s a crucial area for meteorologists. Winds run parallel to the lines. So our winds are coming from Texas-a warm flow. See where the low is in Canada…far north. This is called the “Polar Vortex”.

    Now the same map for next Thursday:

    The Polar Vortex has shifted WAAAAY south, which will drag the arctic air closer to us. Our upper-air winds will be coming from Canada instead of Texas. (These maps are from the European model-the most accurate in the world overall). This is the type of pattern that can eventually give us some snow and/or ice.

    But will this pattern last, or just change back after a week or so? In order for an extreme pattern to persist, we need to see a “blocking pattern” in the upper atmosphere. In this case, HIGH pressure near Greenland can be a key. We call it a “Negative NAO”, which many of you know is associated with cold and snow around here.

    The current upper-air map shows the HIGH centered over northern Europe, but starting to move to the west:

    Now look at the forecast for exactly one week from now:

    The LOW (“Polar Vortex”) has moved far south, leading to a strong flow from Central Canada toward us. And it has the HIGH right over Greenland-the Negative NAO. That’s an impressive blocking pattern, which should keep the cold air in for a while. How long? It’s not clear yet, but the next couple of weeks could be the key to what will happen for the rest of winter.

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