Already, La Niña lives up to its reputation
La Niña is certainly living up to its reputation this season.
Winter hasn’t even started, and we’ve already experienced record sub-zero temperatures, and seen more snow in one month, than we saw all last season.
November snowfall records were broken in both Spokane and Coeur d’Alene last month. Spokane officially received 25.9 inches of snow, surpassing the previous record of 24.7 inches of snow set back in November 1955. Coeur d’Alene saw 38.3 inches of snow, surpassing its old record of 31.6 inches set back in November 1973. These amounts are about quadruple what we normally see so early in the season.
It is interesting to note that La Niña sea surface temperature anomalies were observed in both November 1955 and 1973. Now before you panic that another “snowpocalyptic” winter season is inevitable, here are a couple more interesting tidbits about the winters of 1955 and 1973. Using Spokane data, total snowfall for the 1955-’56 season was 83.2 inches, making it the sixth snowiest on record. The 1973-’74 season was not too bad, however, with 56.2 inches, only about 10 inches above normal.
When it comes to snow and its liquid equivalent, we have already seen both ends of the spectrum. The ratio of snow to liquid water varies greatly depending on the temperature. Very cold temperatures lead to fluffy, “dry” snow that may have a snow-to-liquid ratio (SLR) of 30-40 to 1. In other words, 30 to 40 inches of snow, would melt down to only 1 inch of water. When temperatures are warmer, close to freezing, the SLR will be much lower, with only 5 to 10 inches of snow melting to 1 inch of water. The fluffy snow may pile up higher, but is easier to shovel because it contains much less water. The highest SLR usually occurs with temperatures around 15 degrees.
Colder temperatures tend to produce smaller snowflakes, and warmer temperatures (near freezing) tend to produce the giant ones. When temperatures are near freezing, partial melting helps falling snowflakes stick together. During one such event in Spokane a couple of years ago, I joked to my husband that we had snowflakes the size of small children falling out of the sky.
The SLR is very important for a meteorologist to consider when forecasting snowfall. Computer models do not spit out snowfall amounts, but can give us information about the moisture content of a storm, and about how much liquid precipitation there might be. Using that data, we convert the liquid precipitation forecast to a snowfall amount, with ratios based on the temperature profile forecast.