December Lite: White Christmas 2012? West Coast “Pineapple Express”

72% Historical chance of a "White Christmas" in the Twin Cities

2011 last "Brown Christmas" in the metro

+10 to +20 degrees vs. average to open December in Minnesota

0" snow cover expected from St. Cloud south by Sunday

"Flake an acre" Little or no snow expected through December 6th

"Pineapple Express" ramping up for stormy West Coast this week

December "Lite"

This is not how the December weather maps used to look.

December 2012 looks to open on an unseasonably mild note Saturday.

As a series of storms slams into the Pacific Northwest, milder southerly breezes will flow into Minnesota form the south.

Image: European Model via Weatherbell

In fact, temperatures could run a full +20F vs. average by next Monday, when highs will likely peak in the 50s over southern Minnesota.

Colder weather will follow the front by Tuesday, but there are already signs of another (brief?) warm-up by next Thursday.

Overall the first week of December looks to start at least +5F to +10F vs. average in Minnesota.

White Christmas: Too early to make the call

Historically there's a 72% chance of a White Christmas (at least 1" snow depth) in the metro. The odds drop to about 56% for Tracy in southwest Minnesota, and are 100% for International Falls and Ely.

Image: MN Climate Working Group

2011 was a "Brown Christmas" in the metro & St. Cloud. Duluth had 3" & International Falls had 4" on the ground Christmas Day.

Here are a few select locations and the historical odds (108 years) of at least 1" snow depth on December 25th.

Tyler 56%

Redwood Falls 61%

Twin Cities 72%

St. Cloud 74%

Fargo/Moorhead 84%

Brainerd & Duluth 97%

International Falls & Ely 100%

The Minnesota Climate Working Group has more.

Will we have a white Christmas? It's an age-old question that occurs to almost everyone this time of year. The chances of having a white Christmas vary even here in Minnesota. Having a white Christmas is loosely defined as having 1 inch of snow on the ground on Christmas Day. The snow depth at most sites is measured once a day, usually in the morning. The best chances of having a white Christmas is almost guaranteed in the Boundary Waters Canoe Area and a good part of the Arrowhead. The chances decrease to the south and west and the best chance for a "brown" Christmas is in far southwest Minnesota where chances are a little better than 60%. Northern Minnesota is one of the few non-alpine climates in the US where a white Christmas is almost a sure bet.

In 108 years of snow depth measurements in Twin Cities, a white Christmas happens about 72% of the time. From 1899 to 2011 there have been 32 years with either a "zero" or a "trace." The last time the Twin Cities has seen a brown Christmas was 2011. The deepest snow cover on December 25th was in 1983 with a hefty 20 inches. It was also a very cold Christmas in 1983, with the high temperature of 1 measly degree F. It was not the coldest Christmas Day in the Twin Cities. That dubious award goes to 1996 with a "high" temperature of 9 below zero F. The warmest Christmas Day in the Twin Cities was 51 degrees in 1922. There was not a white Christmas that year. In fact, the Minneapolis Weather Bureau log book for that day states that the day felt "spring like."

"Pineapple Express" ready to deliver massive rain to the West Coast:

The first salvo of the winter season is aiming at the West Coast. A strong jet stream and moisture plume known as the "Pineapple Express" packing deep tropical moisture.

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Image: NOAA

These "Atmospheric Rivers" can produce as much as 50% of California's annual rainfall.

The series of storms will deliver as much as 6" to 12" of rain from San Francisco north to the Oregon & Washington Coasts in the next few days.

NOAA/HPC

Climate Central's Andrew Freedman has more on these amazing "Atmospheric Rivers" that can deliver massive moisture and rainfall to the West Coast and other regions.

Atmospheric rivers occur when winds draw moisture together into a narrow region ahead of a cold front, in a region of very strong winds. They can be thought of as tropical connectors that feed tropical moisture into more northern latitudes. In California, one type of atmospheric river is also known as the "Pineapple Express," since it transports water vapor-laden air from Hawaii into the U.S. mainland.

Research shows that atmospheric rivers are a key source of water in the West Coast, where 30-to-50 percent of yearly precipitation occurs from a few atmospheric river events, according to the National Oceanic and Atmospheric Administration (NOAA). When atmospheric rivers stall, though -- as one is forecast to do for a period lasting roughly Thursday through Sunday -- major flooding can result. While rivers are not currently running very high in Central California, there is still a risk of some flooding this week

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This moisture plume looks suspiciously like an "El Nino driven event" to me. Though El Nino has not developed (yet) in the Tropical Pacific, SST's are notably warmer than average north of Hawaii.

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Let's see what happened in the next 6 weeks. Will this be the start of a parade of storms to hit the West this winter?

Stay tuned

PH