Snow!!!
During the last week, we’ve seen some of the only snowfall to grace the western Washington lowlands this year. While people obsessively check the forecast, it is appropriate to look into the why and how of local snow.
First, why don’t we get much snow? The greater Seattle area has a fair amount of precipitation and moisture every year, with an annual average of 149 wet days and 37 inches of rain. We are also at a high latitude. Still, we only get about 5–6 inches of snow on average.
Well, the answer has to do with geography. Both freezing or close to freezing temperatures all the way from the clouds to the ground and lots of moisture are required to create a good, sticking layer of snow. The weather systems that bring in moist air are also usually the ones that bring in warm air, since they are coming off the Pacific. One prominent example is the atmospheric river called the “Pineapple Express”, which brings warmth and moisture from the Tropical Pacific to the North American west coast, fueling large amounts of precipitation. Meanwhile, weather systems that bring cold air in are usually dry and come in from north of the region. These cold fronts are regulated by the winds from the Pacific so that the area does not get to freezing temperatures for most of the winter.
Most snow in the Puget Sound region is formed by a warm, moist front from the Pacific colliding with a cold front from Canada in a specific way. This means that occasionally you get a Snowpocalyse-like result, but more often than not, there’s only a tiny amount of snow per year.
Another effect is that dangerous phenomena like sleet, freezing rain, and ice are common. Since temperatures are cold, but not super cold, a cycle of precipitation melting and freezing again can be sustained for a while.
Unfortunately, this has apparently created a situation where snow is not uncommon per se, but happens just infrequently enough that various local governments don’t attribute very many resources to snow and ice control. For example, Seattle doesn’t have dedicated snow plows; they just outfit trucks with plowing equipment and rely on civilians to clear non-arterial streets.
Snowstorms can be very dangerous, especially combined with the local steep topography. Obviously, snow and other freezing weather can create very dicey conditions for even short trips. Power outages can happen. For people without support and/or shelter, like the elderly and the homeless, it can be much harder to find relief from these dangers.
Of course, snow is fun in some ways. Getting surprise time off from school and work -at least in pre-pandemic times- is great. Winter activities like sledding are possible without going all the way to the mountains. It’s like an impromptu holiday.
With that in mind, I hope everyone enjoys the winter weather while it lasts. Just be careful and remember it’s not all fun and games.
Sources
http://www.seattleweatherblog.com/rain-stats/
http://www.seattleweatherblog.com/rain-stats/
https://oceanservice.noaa.gov/facts/pineapple-express.html
https://www.bbc.com/news/world-us-canada-47189161
http://www.seattle.gov/emergency-management/hazards/snow-ice-and-extreme-cold
https://forecast.weather.gov/product.php?site=NWS&issuedby=sew&product=AFD&format=CI&glossary=1
