Over the past week or so, I have been thinking a lot about the December 2018 to January 2019 snowfall and what it has meant for me as a recent transplant and homeowner living in the town of Los Alamos, New Mexico. I certainly didn’t feel prepared for this event, even though I spent years living in Fairbanks, Alaska! So, I decided to take a closer look at the records to see how this event stood up in terms of past snowfall events.
To examine snow events over the historical record, I looked at the 7-day and 14-day cumulative snowfall in inches at the National Climate Data Center (NCDC)-National Weather Service (NWS) Los Alamos climate station, which began operating in 1910. Events were counted starting from January 2nd to include January 1st in the last part of the year. The top events, as discussed below, are ranked according to size, with events +/- 0.5 inch in magnitude being classed in the same size and rank.
Looking at the 7-day snowfall, 2018/2019 was certainly a big one! About 22 inches fell in total from the day after Christmas to New Year’s Day. Although, this snowfall was not the largest event that has occurred over the past ~110 years in Los Alamos. In particular, 1984 and 1987 were both big years, with not just one but multiple large (in the top ten) snowfall events on record. Between 1960 and 1990, 62% of the top 7-day snowfall events occurred. Since that time, we have had much smaller 7-day events, with several years that were in the 95th percentile of events (orange line in figure). The 2018/2019 snow fall comes in a little below the 99th percentile of 7-day snowfall events (~24 inches), and is the 9th largest 7-day snowfall event on record, tying with the 1948, 1978, 1987 and 2001 events. Perhaps most importantly, it has been 18 years since the last 7-day snowfall event of a similar magnitude, which occurred in 2001.
The 14-day snowfall events tell a different story. Looking at these events, we see that 1987 is the largest snowfall year, followed by 1984, with these years having 6 of the top ten 14-day snowfall magnitude events on record. The years 1961, 1982, 1975, 1967, and 1960 are also in the top five of 14-day magnitude snowfall events. There are also several large events that occurred after 2001, which was tied with 1975 and 1967 as the 4th largest 14-day snowfall event on record. These include the snowfall of December 2006, January 2004 and March 2005 (which is tied with 2018/2019 snowfall in magnitude). Thus, we’ve had multiple 14-day snowfall events in the past few years, although it has still been about 10 years since a similar magnitude 14-day snowfall event has occurred in Los Alamos.
Thinking about this in terms of return levels (or the amount of time between events), based on the historical data, the 7-day and 14-day snowfall event we received starting on December 26th, 2018 is anticipated to occur about every 3.5 to 5.6 years. Why haven’t we seen these events in the past 10-18 years? Well, if you look at the plot to the left, I show temperature differences from the 30-year time period that we did get a lot of snow (1961-1990s). The temperature differences show us that since the late 1990s, temperatures have been getting warmer on average due to climate change. The warming we have seen in the Southwest has been linked to drought, and has many different impacts, including changes in snowpack, which has consequences for river systems, ecosystems and fire around Los Alamos.
Some caveats of this analysis, snowfall might not be the best metric to look at it, but unfortunately it is only snow value that has been consistently recorded since the early 1900s at the NCDC-NWS climate station. There are several other records of snow water equivalent (Quemazon SNOTEL), and snow depth (also NCDC, and LANL stations), but those records and stations do not go back as far the NCDC-NWS snowfall observations. Also, the date of the first day of record matters, so if you did this analysis using slightly different 7-day and 14-day windows, you would get a slightly different answer.