The hype is building in the Emerald City for a possible “megastorm”of historic proportions tonight and Wednesday. Snow total forecasts of over one foot are being tossed around. But officially, the National Weather Service (NWS) is calling for 5-10 inches in Seattle and some forecast amounts are falling.
Including media forecasts and bloggers, predicted amounts range from 2-12”+ for the greater Seattle area. Irrespective of exact amounts, the incoming storm promises to have major impacts across the Puget Sound region and nearby mountains.
The combination of heavy wet snow and strong winds may cause power outages in some areas and travel is likely to be difficult, especially during the day Wednesday, when the snow is likely to be heaviest.
In Seattle, a 10-inch snowfall would be the most since 1996 according to the Seattle Times. Seattle’s long-term annual average snowfall is 11.7” but just 5.9” from 1981-2010.
Last night, NWS had forecast 6-14” of snow for Seattle, but has adjusted amounts downward. If somehow the storm overachieves and 14” actually falls, it would be the most snow there in 50 years (14.9” fell on January 27, 1969).
Cliff Mass, a professor of atmospheric science at the University of Washington who blogs about the local Seattle weather, cautions “this is a very difficult forecast.”
“Everything depends on getting the track of the low exactly right...first to decide where the rain/snow changeover will be and secondly to get the amount of precipitation right,” Mass wrote in a blog update this morning.
KOMO News, a Seattle television affiliate, splits the difference between Mass’ and NWS’ forecast, predicting 4-8”. The affiliate KING offers a larger range, forecasting 4-12”. Accuweather calls for an “immobilizing snowstorm” and says more than 12” could fall.
By Thursday, enough warm air is likely to work into Seattle to change snow to rain. (KING 5 forecaster Jim Guy, however, notes “newest guidance suggests that may not happen everywhere.”) In the mountains, AccuWeather cautions “the combination of the excessive snow now and rising temperatures later in the week will increase the risk of avalanches.”