Melting Away in the January Thaw

Milwaukee – Is it warm where you are?  If you live in most of the United States and Canada, it probably is. The western United States, western Canada and Alaska are the only locations with below average temperatures on January 18th. After a cold beginning to 2017, the temperature tables have turned and we are looking at a week or more of warm temperatures. And this isn’t slightly above normal warmth. This is potential record warmth for some locations. In other words, this January 2017 thaw has some chops.

We are now moving towards the end of January and the next week to ten days looks warm. This is happening, when we are moving, climatologically, through the coldest part of the year. So, what gives? What is going on?

Define January Thaw

First, we need to define the January thaw.  According to the Farmer’s Almanac, the thaw is very noticeable because it arrives in the last week of January; lasts about a week and temperatures are about 10°F above normal. The almanac isn’t the most scientific organization.  So, what does the National Weather Service (NWS) conclude? The NWS is a part of NOAA and the Department of Commerce. NOAA defines the January thaw as a period of relatively mild temperatures between January 20th and 23rd. A quick look at other sources on the internet shows that most definitions are a blend of these two.

End of January Forecast

Well, for snow lovers living east of western North America, this next image is not promising. This is the temperature forecast through January 27th.

Fig. 1 Temperature Probabilities
Fig. 1 Temperature Probabilities

The area in red and orange is a high confidence forecast for above average temperatures – 70% and higher in the Great Lakes and New England. The blue area shows below average temperatures with a peak of 70% in Nevada and Utah. Again, these are high confidence forecasts that will confirm. If you live in the red and orange area, this means most and maybe all of your snow, if you have snow on the ground, will melt by January 27th. If you live in the blue area, snow will accumulate, especially at higher elevations.

The thaw is already starting. Here are two graphics of the atmosphere for January 18th. Figure 2 is a look at around 16,000 feet above sea level. Note the areas in orange and red over the Great Lakes and Canada.

Fig. 2 500mb Height Anomalies                    Fig. 3 850mb Temperature Anomalies

These areas show significant height rises above long term averages. This is a signature for warmer temperatures – the larger the anomaly, the larger the temperature departure, for the most part. This warm up is confirmed in the Figure 3. Figure 3 shows temperature anomalies around 5,000 feet above sea level. There is a large area of deep red over the central United States and Canada.  Locations in red have temperatures .9°C or warmer at 5,000 feet above sea level as of January 18th. In many areas, the warm air is overhead and in place. This pattern and the warmth will stay in place through next week.

Winter Does Return

Confidence is growing that cold air returns between January 25th and 27th. Multiple forecast models are showing a pattern change the last full week of January. This pattern change gives the western United States a break from intense storms and atmospheric river that has dumped feet of snow and inches of rain from California north to Washington.  It also means that cold air returns to Canada and the United States from the Arctic.

Here are two images for late January. Figure 4 shows anomalies at 500mb and Figure 5 850mb.

 Fig. 4 500mb Anomaly Jan 27th                        Fig. 5 850mb Temp Anomaly Jan 27th

Similar to figures 2 and 3 above, Figure 4 shows above average heights shifting to the high latitudes of Canada with a peak in northwest Canada. The blue areas in Figure 4 show heights below average. The greater the change in heights at 500mb, the more you can expect temperatures to change – positively and negatively. This again is reflected by the 850mb temperature anomalies. In Figure 5, areas of blue shows below average temperatures in degrees Celsius over the Central United States. Black, the most abundant color, is slightly below average. The orange to red areas show above average temperatures in northern Canada. Note how these anomalies in Figure 5 align with Figure 4.

After a week of melt, in the north, or an early spring, in the south, expect the cold to return. Then we can start talking about the next round of snow and ice. Enjoy the break from the intense cold. Winter shall return!

Meteorologist Mark McGinnis is on Facebook, LinkedIn and Twitter @fairskiesconsul