WeatherWatcher: Cold weather, White Christmas Possible

Sunday, December 23, 2012

Shoreline Weather
  • The week ahead - possible slushy or white Christmas
  • Last week's highlights
  • Last week's weather data
For the next week: It's going to get a little interesting. Christmas Eve will be mostly dry but chilly. Clearing in the afternoon and overnight into Christmas morning will allow for the air to drop below freezing. A storm front off the Pacific ocean will move in before dawn, trapping the cold air in place for a start of snow, maybe mixed with rain. We could see a wet, slushy inch or two of snow before it mixes over to rain. Most models agree that the snow level will start at 500 feet and go up, so only places like the Richmond Highlands and North City Business district have the best chance of accumulating snow. It might get a little colder but it is really on the border line with this storm. As of now there are no winter watches or advisories in effect.

The rest of the week looks like it is going to bring rain, however, it will remain chilly with temperatures topping out either in the upper 30's or very low 40's, much the same as we have had this week. Beyond, things may turn a little colder for more possible white stuff.  Keep in mind whenever we have weather patterns promoting temperatures in the 30's it doesn't take much to drop the snow level, so be prepared for at least the threat of winter weather. 

A white Christmas is defined by at least 1 inch of accumulated snow on the ground. The greater Seattle area's normal chance of a white Christmas is less than 10%. Our last White Christmas was in 2008, and before that was 1990.

Last week we received a lot of precipitation. 3.86 inches of rain was measured in the rain gauge, some of it however was probably melted snow, which isn't measured as precipitation until it melts. Tuesday morning there was a brief accumulation of snow before it melted off by around 6-7am. Wednesday morning there was some snow fall making about 1 inch of wet accumulation before it turned over to rain in the afternoon.

Last week's data:
High temperature: 44.2ºF (Monday)
Low temperature: 29.5ºF (Friday)
Rainiest day: 1.5 inches (Wednesday)
Total rainfall: 3.86 inches
Warmest day: 39.3ºF (Monday)
Coldest day: 35.4ºF (Tuesday)
Average temperature: 37.1ºF (0.5ºF below average)
3-Year average temperature: 37.6ºF

Warmest and coldest days are based on average temperature of the entire day, starting at midnight. All other averages are based on the whole week, starting Saturday morning at midnight. All weather data unless otherwise noted is sourced from Carl's Shoreline Weather.

For fall and winter storm updates, check out my weather station web page or follow me on Twitter: @SWeatherWatcher

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