Massive West Coast storm to trigger Midwest thaw

They say a butterfly can flap its wings in China and cause a hurricane in the Caribbean.

That oft used chaos theory paraphrase is a subtle reminder that weather is linked over space and time. What happening on the West Coast this week and the related effects on Minnesota are anything but subtle.

It's more like a 2x4 whack on the side of the head.

The bottom line is when major winter storms batter the left coast, mild Pacific air masses usually follow in Minnesota.

The surface map animation above tells this week's story. A powerful low pressure system drives heavy rainfall into the coast, and pushes a Pacific warm front east of the Rockies toward Minnesota in the next 48 hours. Meanwhile a strong nor'easter dumps coastal rain and heavy snow back east.

Many media outlets in the Bay Area are calling this the biggest storm in decades for Northern California.

The storm hits the Washington state and Oregon coasts later tonight, and batters northern California tomorrow night and Thursday. Rainfall totals with the system look ridiculous, with 3 to 8 inches in northern California. High winds, power outages and heavy mountain snows are just over 24 hours away.

The hardest hit areas for rainfall will be along the Washington state and Oregon coasts. As much as afoot of rain may trigger mudslides and debris flows this week. Here's the seven day rainfall forecast from the National Oceanic and Atmospheric Administration. Several feet of snow will bury the high Sierra and Cascades.

December thaw kicks in

The western storm pushes a gush of Pacific air east into the Midwest by Thursday. Take a look ta the forecast temperature anomalies by Saturday morning in the central United States. Temps 10 to 20 degrees warmer than seasonal averages gush into the Plains.

The weekend numbers continue to come up mild for Minnesota. Temps in the 40s are a lock, and we may push close to 50 degrees in the metro and southern Minnesota by Saturday and Sunday.

Temps above freezing even at night this weekend?

Disappearing snow cover

It's remarkable how much snow cover has dwindled over the US in the past three weeks. On Nov. 18 an impressive 50.2 percent of the lower 48 U.S. was covered with snow. Snow cover extended all the way south to Texas.

Today just 18.8 percent of the U.S. is sporting snow cover.

Obviously when winds shift into the south the air mass will warm more than usual for December as it travels over bare ground to the south.

There are some big holes in snow cover over Minnesota. I expect most all the snow in the southern two-thirds of Minnesota will be history by Sunday.

• 1 inch Snow depth at Minneapolis-St. Paul International Airport today

• 2 inches Snow depth at St. Cloud, Minn.

• Trace snow depth at Fargo, N.D.

• 0 inches snow depth at Sioux Falls, South Dakota

I'd put the odds of a brown Christmas at 50/50 for the metro right now. There are some hints of cooler temps and light snow in the week leading up to Christmas. We could squeak out an inch or more before Dec. 25. There are also signs of another possible warm push by around Christmas Day.

Stay tuned.