Polar vortex to drive more Arctic air south

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WEST MICHIGAN — I know the term polar vortex was used, abused, and over-used last year with a nasty, prolonged Arctic outbreak. Frankly, it seems these days everybody blames the polar vortex. That said, blame it again as reinforcing Arctic air will plunge south from Canada in to the Great Lakes Tuesday night through Thursday night.

While the polar vortex itself is a semi-permanent circulation at/around the north pole, lobes of Arctic air can break off and drop south in the the United States. The vortex itself is comprised of a huge cyclonic, counter-clockwise circulation that is clearly evident on 500 millibar weather maps about 18,000 feet above the surface. Take a look at that map below. Note the huge low and circulation of the vortex over James Bay in Canada. This forecast snapshot is valid for Wednesday morning.

Wed 12z

On the next snapshot valid Thursday morning, the vortex and low are quite prevalent dropping further south and entrenching all of the Great Lakes and Northeast with an Arctic blast. See below.

Thu 12Z

As I told our other FOX 17 Meteorologists…I have not in 14 years of forecasting West Michigan weather ever seen atmospheric thicknesses of 488 meters. Recall that as the atmosphere heats up…like many other things, it gets thicker and hence thicknesses increase. As Arctic air plunges in, atmospheric thicknesses decrease. I’ve seen thicknesses around 492 to 498 (which is still very cold), but 488 is indeed rare. So yes…there is a relationship between temperature and atmospheric thickness. That said, meteorologists also examine temperatures about 5,000 feet above the surface. That would be called the 850 millibar level for you weather geeks. I also have not seen those temperatures at -26 to -28 degrees Celsius here in Michigan. For clarification, upper air charts/maps are always in degrees Celsius. To translate, -28 degrees Celsius would equal 18 degrees below zero Fahrenheit. At the surface, we likely wouldn’t get above zero! Take a look at the forecast model snapshot of 850 temperatures valid Thursday morning.

GFS Temps

The above map also shows the wind direction…northwest to west/northwest over Michigan too. Since our forecast models are showing little/no temperature inversion on Wednesday/Thursday, the Arctic blast and waves of energy pivoting around the vortex may generate several inches of lake-effect snow, especially along/west of U.S. 131. In fact, I envision the possibility that some areas may see a foot or more from Tuesday night through Thursday night until the vortex, deep upper level trough, and core of Arctic air lift out of the region. It would be a very light, fluffy, small-grained snow. An FYI…a temperature inversion is where temperatures warm as you move upward in the atmosphere. With a high inversion around 10,000 feet or no inversion in place, snow/clouds can build upward and produce higher accumulations than inversions around 5,000 feet or less. Low temperature inversions actually help keep a lid on snow production and accumulation amounts.

I should also mention that the image attached to this story shows the polar vortex in place on Wednesday morning (upper level pattern), and the colors represent the air masses. Again, it’s rare that we see a light pink or white over the area. Note also that the Arctic air, polar vortex, unsettled weather, and increased snow chances are all associated with an upper level trough over the area. That trough allows the colder air to sink southward. The opposite of a trough is a ridge. Both are the same premise as a trough-ridge radio wave pattern. Troughs typically equal colder/unsettled weather, while ridges are typically quiet, uneventful weather.

Bottom line? Get ready for a potentially brutal week if these forecasts model verify! I expect accumulating lake-effect snow and even more brutally cold Arctic air for us this week. Get the complete forecast including temperatures, wind chills, satellite, and radar at www.fox17online.com/weather.

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