Estimated current snow depths in the Pacific Northwest. In the higher elevations several additional feet may fall on top of this snow cover and even several inches to a foot in lower elevations around Seattle. (NOAA)

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.

Winter storm warnings are posted for much of western Washington. The high elevations of central Cascades may see several feet of snow. Some spots may see 40” in just 24 hours.

Snow blankets the roof of the famous Pike Place Market in Seattle January 15, 2012, while a ferry floats past West Seattle in the background as snow continues to fall during the Puget Sound region's first major storm of this winter. (ANTHONY BOLANTE/REUTERS)

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.

People push a car uphill next to a bus showing an travel advertisement for skiing in Montana, Sunday, Jan. 15, 2012, in Seattle. Several inches of snow fell quickly Sunday morning, snarling traffic and clogging roadways. (Ted S. Warren/AP)

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.”