WeatherWatcher: Larger cold outbreak on the way

We have a major weather pattern shift occurring this weekend that is going to make December's cold air bursts look like just a few warning shots.

The National Weather Service in Seattle has even issued a special weather statement regarding the likely snowfall and cold weather taking hold. The good news is, there isn't a large amount of snow in the forecast at this time. The transition to the cold pattern is expected Saturday evening into New Years Day.

Snow: Accumulating snowfall is expected up to one inch or more Saturday evening into Sunday morning. There is still uncertainty as to the amount but it is likely that at least one inch will fall. Temperatures after the snowfall will not break the freezing mark for the forecasted future well into next week Friday. This means any snow that does accumulate will stay around for a while.

Cold: Models short term and long term show no end to this major pattern cycle that is expected to keep us in the ice box for 1-2 weeks or more. This pattern additionally leaves the door wide open for storms to bring us snow events as there is no real blocking high pressure protecting us overhead.

Here's NOAA's 6-10 day temperature probability outlook for January 4th - 9th.

The message is that it will be cold.

The basic set up has a upper level ridge over the Gulf of Alaska, forcing the jet stream in the Western Pacific to move north through Alaska and the Arctic and then southeast just off shore of the North American coast well past the Northwest into California.

This upper level circulation pattern is not unheard of. It has happened many times in past cold winters for our region. Other winters that had this upper level circulation pattern are December 2008, January 1969, and December 1950.

Here's some short statistics from these examples of Seattle winters that experienced this upper level pattern:

• December 2008 had a total snow accumulation of 13.9 inches reported at Sea-Tac. January, February and March that same winter recorded another 9.4 accumulated inches of snowfall in smaller snow events.
• December 1968 - January 1969 Sea-Tac recorded 67.5 inches of total snow accumulation spread across several events. December had 22.1 inches and January had a whopping 45.4 inches.
• January 1950 was known for the Seattle Blizzard of 1950. Friday January 13, 1950, the blizzard moved in from the Pacific with strong winds and temperatures dropping down to 10°F. That month 57.2 inches of snow was recorded at Sea-Tac.

So the challenge with these storm totals listed above is that there weren't very good records kept here in the Shoreline area before recent decades. With any snow event there is always a large variability from Sea-Tac to Shoreline.

Bottom line: This is a serious cold pattern, we are looking for low temperatures to be in the teens and high temperatures to be in the upper 20's for all of next week. We might break past the freezing mark during the peak of the afternoon for a short time one or two days next week. The door is wide open for a major snow event next week. It is just too early to tell what will happen right now, but if this cold and upper level pattern holds true to what models indicate we are wide open for a significant snow event within the next two weeks.

Not to scare anyone of course, but be prepared for the possibility of winter weather that we haven't seen in at least 8 years.

For current weather conditions visit www.shorelineweather.com