After a modest round of wintry weather over the weekend, more snow, including a potentially historic winter storm will target the Pacific Northwest this week, with heavy accumulations expected, even in Seattle.
In the Cascades of Washington and Oregon, snow will be measured in feet and along some western-facing slopes, it could take multiple yard sticks to total up the powder!
A cold Arctic outbreak thanks to frigid high pressure centered over southwestern Canada is providing the cold air for the snow, while an onshore flow from the Pacific is adding in the moisture.
With several rounds of moisture poised to move ashore, the snow will continue to come in phases as indicated by Edwards. The first round delivered more than 2 inches of snow to Seattle on Sunday, marking the first measurable snow of the season.
Another round will continue through today, with much of western Washington and Oregon poised to experience accumulating snow. In the Portland area, the snow will mix with rain, while plain snow is on tap again for Seattle and Bellingham.
By tonight, at least 3 to 6 fresh inches of the white stuff will be on the ground around the Emerald City, with heavier amounts along the hills to the east.
The snow map above is available in a larger version at the AccuWeather.com Winter Weather Center.
The worst conditions will arrive across the Northwest later tonight and Wednesday as a moisture-laden and powerful storm slams ashore.
There are still some questions concerning how much warm air the storm will push inland, but the potential exists for an historic amount of snow in some areas, including the greater Seattle area, where more than a foot is a strong possibility. Eventually, a changeover to rain is expected on Wednesday.
Warming air should spare Portland and Eugene of significant snow totals altogether.
Characteristically, snow totals will be much higher in the Cascades and will threaten travel through major passes. As Ken Clark points out in his blog, several feet of snow is possible even at pass levels.
Snoqualmie and Sherman passes are at a relatively high risk of being closed during these snow events, especially with the storm expected to hit early on Wednesday.
Heavy snow amounts will also extend across inland and mountainous areas of eastern Oregon, Washington, Idaho and western Montana by midweek.
Back along the I-5 corridor from Portland to Bellingham, travel will be treacherous this week, and could turn out to be dangerous for a time midweek.
Though heavy snow is relatively rare, Seattle is not immune to significant snowstorms.
"Single day snowfall of 6 inches or greater has occurred on only 15 days since 1950, none since 1996," said Climatologist Jim Rourke.
"The top Seattle snowstorm was Feb. 1, 1916 when 21.5 inches piled up," added Rourke.
Senior Meteorologist Kristina Pydynowski points out another potential threat: major flooding.
"Despite the exact outcome of the snow in the middle of the week, a parade of warmer storms late next week that follow will deliver heavy rain, putting the Seattle area at risk for major flooding," says Pydnowski.
Roads turned into rivers in parts of the mid-Atlantic on Saturday due to flooding downpours.
Rounds of drenching showers and heavy thunderstorms will heighten the risk of flash flooding across the northeastern United States through the final weekend of July.
After unloading flooding rain across the Philippines into Monday, Typhoon Nida will take aim at China early this week.
A tropical wave approaching the Caribbean Sea will attempt to reactivate the Atlantic Basin during the first week of August.
As several large fires continue to rage across the western United States, weather conditions will gradually improve for firefighting efforts this week.
Additional downpours are likely to roll across northern New Jersey and further suspend play during the late rounds at the 98th PGA Championship at Baltusrol Golf Club this weekend.
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No 90 degree reading in Central Park in all of June and July - the first time on record this has happened.
Kanata, Ontario, Canada (1996)
A severe thunderstorm downed electrical wires and trapped people in their cars and a bus for 1-2 hours. Amazingly, nobody was injured.
Scituate, MA (1769)
Hail fell 12" deep and remained on the ground for 30 hours.