AccuWeather.com

By Alex Sosnowski, Expert Senior Meteorologist

Jan 17, 2012; 5:46 PM ET

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Ken Cunningham shovels his sidewalk during a snowstorm in Seattle, Sunday, Jan. 15, 2012. More snow is falling on the Emerald City and the storm could make the top 10 list of heaviest snowstorms on record. (AP Photo/Ted S. Warren)

The snow into Thursday could end up being one of Seattle's biggest snowstorms on record.

The storm and its heavy snowfall have the potential to close passes in the Cascades, clog streets at sea level with tons of snow and slush and force flight delays and cancellations.

Near the coast, the snow will be heavy, wet and difficult to shovel. The combination of heavy, wet snow with gusty winds in some areas will down trees, taking power lines with them.

In the mountains, a yard or more of snow will fall in the high country. The combination of the excessive snow now and rising temperatures late in the week will increase the risk of avalanches.

Heavy snow was hitting the swath from Olympia to the southern Seattle metro area today, where the snow could come down at an inch-per-hour pace at times.

Grand Mound, near Olympia, along I-5 in southwestern Washington has received 23 inches of snow from the storm thus far. So as far as record-breaking snowfall, interior southwest Washington seems to be the place with this storm.

RELATED:

Northwest Snowstorms to Reach Midwest, East, California

Mother Nature's turn for the worse in the Northwest should come as no surprise as the stormy weather has been well-advertised.

As temperatures rise and rain falls near sea level later during the series of storms this week and beyond, urban and poor drainage area flooding can occur.

The storms will continue to push across the nation from the Pacific over the next couple of weeks. The pattern will bring rain and mountain snow to much of California before it is all said and done.

A larger version of this map is available on AccuWeather.com's Winter Weather Center.

The same pattern will also treat some northern tier states of the Rockies, Plains, Midwest and Northeast with snow and ice events in the days ahead.

In Seattle, snowfall into Wednesday will rival two storms in November 1985 and others that occurred in the 1970s and 1960s.

While this storm will fall short of the blockbuster storms of 1880, 1916, 1950, 1969 and 1996, a foot of snow could accumulate in part of the Seattle-Tacoma area.

Unlike most storms over the Midwest and East, which drop their load of snow in a matter of hours, storms in the Northwest often last days. In many cases, the biggest snowfalls in Seattle and the Cascades are a series of storms all jammed together.

Being so close to such a large body of water and mean steering winds which drive all of that Pacific Ocean moisture ashore in rapid-fire fashion has a lot to do with the nature of the storms in the Northwest.

According to Western Weather Expert Ken Clark, "Most often the flow off the Pacific Ocean drives the temperature up just past the freezing mark almost immediately, bringing rain instead of snow. However, on rare occasions, such as this, a cold, low-level flow off the land holds out, while tremendous amounts of moisture fly in overhead off the ocean."

We did some research on snowstorms and series of snowfalls that have hit the Seattle area. Records in the region date back to the late 1800s. (Special thanks to AccuWeather.com Forensics and the National Climatic Data Center.)