Wednesday, February 1, 2017

Winter? What Winter?

Today marks the start of the last third of winter, climatologically speaking. The winter statistics will be calculated over the months of December through February, even though in many areas winter weather can continue through March and into April. So, where are we at with a month go go in official winter?

One quick way to look at the status of the winter season is to look at a map of the Accumulated Winter Season Severity Index (AWSSI). The AWSSI (pronounced "aww-see") is an index that scores the impact of cold and snow (both snowfall and snow depth) occurring during the winter season. The index was developed by Barbara Mayes-Boustead with the National Weather Service in Omaha, NE, and yours truly. Scores fall into one of five categories ranging from Mild to Extreme. Here is the map as of January 31 showing how winter is progressing across the country.

The categories of the Accumulated Winter Season Severity Index as of January 31, 2017

As you can see from this map, this winter has been particularly severe in the northwestern quarter of the nation from the Pacific Northwest down through the northern Rockies and into the Northern Plains. Over the rest of the country, winter so far has been mild.

Here are the temperature departures for the period from December 1 through January 31. The areas of the country that have experienced warmer than normal temperatures also tend to have below normal snowfall.


Snowfall, as you no doubt have heard, is heavy across the western U.S. More snow is expected over the next several days as another storm slams into the coast.


As of this morning, snow cover is extensive over the western U.S. and across the northern tier of states into New England.





We can look at the progress of the AWSSI though the season by plotting the score for each day through thee season. Individual storms or snowy periods and cold periods can be seen by the sharp changes in the AWSSI plot, The shading on the chart shows the envelope of all AWSSI scores for that location and the five categories for that station. For example, here is the plot for Redmond, OR.



Redmond's normal seasonal snowfall is around 16 inches and annual precipitation is 8.90 inches. Oregon State CoCoRaHS Co-Coordinator Jim Jones, who lives in Redmond, reports that he has measured a total of 47.9 inches of snow since December 1, and 4.39 inches of precipitation, about half the annual total..

In contrast to the extreme winter weather in Redmond, let's take a look at the AWSSI this winter in Utqiaġvik (formerly Barrow), Alaska. The AWSSI is at a record mild level in Utqiaġvik. As of today the score was 1570, and the previous record low on February 1 was 1965. At the rate the winter is going it is not likely to climb out of record mild territory.



You an follow the AWSSI through the rest of the winter and learn more about it at the Midwestern Regional Climate Center's AWSSI page.

Tuesday is Groundhog Day, so Punxsutawney Phil will allegedly tell us how much winter is left (but you get a better forecast just flipping a coin). Four to six weeks more of potential winter weather (i.e. until the beginning or middle of March) is a pretty good bet in almost any year. Sorry, Phil.