Friday, January 2, 2015

Tropospheric Polar Vortex May Deliver Record Cold on January 7-9th

Nearly one year to the day after the tropospheric polar vortex was sent into southern Canada to bring record-breaking cold into the United States, model guidance is unleashing another round of record cold to kick off 2015.

Before we get started, please read this infographic from the National Weather Service to understand what the polar vortex is and is not.

*Note: The controversial phrase 'polar vortex' is used in this article for purposes of communication to the public, instead of 'Massive Arctic Semi-Permanent Upper Level Low', which would not only be too long to type over and over again, but is also not as effective at communicating this threat to others. 

Tropical Tidbits
The above image shows the European model ECMWF's forecast of 500mb geopotential height anomalies, for the evening of Wednesday, January 7th. Note how we see strong high pressure forcing its way into the Arctic from the Bering Sea. This dislodges the tropospheric version of the polar vortex, and seemingly splits it into two bodies; one just east of Greenland, and another in the East US. That dark blue area represents the lobe of the polar vortex, and if you closely observe the 500mb height contours on this chart, you can see that the lobe gets as far south as the border of New England and Canada before shooting east. The GFS model agrees on this polar intrusion.

So... what can we expect for this latest cold blast?

Tropical Tidbits

Now switching to the American GFS model, as ECMWF temperature products are pay-to-view and may not be posted on this website, we see the cold really begins to set in on the morning of January 7th. We see temperatures on the surface of -25 degrees Fahrenheit over the Dakotas, with major cities like Des Moines, Chicago, Milwaukee, and Minneapolis all sub-zero. Similar to the Arctic air outbreak last January, this is pure Arctic air. This is dangerous and potentially life threatening, IF current forecasts are correct.

Tropical Tidbits
By Thursday morning, the cold recedes from the Plains to some degree, but hits the Great Lakes hard, as Chicago goes sub-negative-15 degrees on January 8th, with similar fates meeting the Quad Cities, Madison, and even Gary, Indiana. It's very possible that any snow cover put down by the January 3-5 winter storm, as well as the January 5-6 clipper, may intensify this cold blast further than models are predicting.

Although I can not post temperature forecasts of the ECMWF model, here are a few key points that I can paraphrase for you:
- Temperatures by midday Wednesday are sub-zero north of a line from Springfield, IL to North Platte, NE.
- Temperatures on Thursday morning bottom out around -22 degrees F in central Wisconsin, with widespread double-digit sub-zero temperatures around the Midwest and Great Lakes. Madison, Minneapolis, and Chicago all hover around -15 to -20F.

To summarize:

- Model guidance is in agreement on a record-breaking cold blast to hit the United States on January 7th and 8th.
- Temperatures, if forecasts are correct, will plunge below -20 degrees Fahrenheit in the North Plains and Upper Midwest, with double-digit negative temperatures widespread across the Midwest, Plains, and Great Lakes.
- High uncertainty still exists with this event, but confidence is gradually rising.
- Residents across the United States must be watchful of future forecasts, as this will be a deadly cold wave if it comes to fruition.