The image below depicts the average height of the atmosphere at 500 mb of pressure (approximately 18,000 feet above mean sea level) for January 2015 and January 2014. These lines of equal height can also be used to visualize the wind flow in the upper-atmosphere by following the lines.
With just a quick glance both graphics look similar. A trough (dip) in the mean upper-level wind flow centered over Hudson Bay with the flow over North Dakota and Minnesota coming in from the northwest. Yet, on closer examination the trough in January 2014 was sharper and the average height of the 500 mb pressure in the upper Midwest was lower than it was this year. That lower average height equates to lower temperatures. Plus, the flow over eastern North Dakota into Minnesota was more north-northwesterly bringing air from the Arctic directly into the region.
Whereas this year, the flow was more west-northwesterly bringing in a flow with a origin over the north Pacific Ocean, a much warmer air mass source region than the Arctic. With a source region over the north Pacific, in combination with a lack of snow cover this year has meant much warmer temperatures. Below is the average temperature anomaly for January 2015. Temperatures across much of the area finished 5 to 8 degrees above average last month.
With a sharper trough and the upper-level wind flow bringing in more direct air from the Arctic (and often in turn Siberia) January 2014 recorded much colder temperatures than January 2015. Yet western North Dakota with a lack of snow cover did still manage above average temperatures last year. But eastern North Dakota, especially the Red River Valley recorded temperatures 5-7 degrees below average and maintained a snow pack the entire month. That made for a difference of 10 degrees from last January to this year in many locations in eastern North Dakota and northwestern Minnesota.
Probably forgotten in the past year by most was that January was warmest of the three principal months per temperature anomalies during the winter of 2013-2014. Both December (2013) and February (2014) recorded temperatures around 10 degrees below average.
With our flow this winter having subtle differences in the storm track has meant either the fast moving “storms” coming through the northwest flow have either gone through southern Canada and brought snow along and north of Highway 2 per the example below:
The other principal track as tended to be south of the Highway 10/Interstate 94 corridor per the example below.
The reality is a vast majority of the Northern Plains have recorded below average precipitation this winter. It is just those two tracks of lighter snows have been the most persistent for the past couple of month. With Fargo Moorhead situated in between those two dominate scenarios is why the metro has yet to record a 1 inch snow from any one singular event this season. That could easily change tomorrow as a storm takes a track through the middle (I94 corridor) of those two tracks tomorrow and therefore looks to be the best opportunity for more than a dusting of snow in and around Fargo Moorhead.