Let me grab more examples, I could come up with more, but that would probably bore some of you to death, and after a while you should see the pattern, if anything getting a shortwave to crash into California is probably very beneficial for most of the board to score big. In a La Nina pattern like we have now with plenty of cold air and a very extensive, persistent vortex in SE Canada and the Great Lakes and dominant northern stream, and no blocking over north-central Canada or Greenland to create an atmospheric traffic jam over east-central North America, we have to get shortwaves to crash into California and cut-off from the northern stream to give us any chance whatsoever for a major board-wide winter storm. Sure, it could get milder in advance of the s/w but you do realize we have absolutely no chance of a big board wide event with the pattern we have now right? Just to reiterate, putting a shortwave into California would allow us to finally tap into the rich Gulf of Mexico and central-eastern Pacific moisture and amplify the southern branch of the jet. Without this critical piece of the pattern, a big, board wide storm is probably not happening, as we've observed with the last 3 busted threats which have all originated from shortwaves entering the Pacific NW or Northern Rockies...
Here's a 500 hpa geopotential height (contours), wind (wind barbs), and vorticity (shaded) animation via ECMWF's 20th century Reanalysis for the February 1973 snowstorm. Notice in the beginning a shortwave embedded within the subtropical jet, enters the North American continent through southern California & the Baja Peninsula of Mexico. The strong El Nino at the time likely gave a major boost to this shortwave and contributed to this s/w remaining very intense so far south.
Earlier that same year, another major winter storm in early January, which produced a historic ice storm in the Atlanta metro area and resulted in several inches of snow in portions of NC & upstate SC. The shortwave which triggered this event crashed into California on January 5th, and a piece cut off from the mean flow and merged with another s/w over the east-central subtropical Pacific and lifted northeastward into the southern Plains and lower MS valley on the 7th, producing a lot of snow & ice from GA to the Carolinas in the process. This 500 hPa geopotential height, wind, and vorticity animation, like the one above, is also from ECMWF's 20th Century Reanalysis dataset.
February 28, 1980, immediately before a major blizzard broke out in eastern NC (which dropped more than 1-2 feet of snow for a majority in the eastern part of the state), the shortwave that triggered the event enters the US through central California
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January 11, 1982, immediately preceding the infamous "snow jam" event in Atlanta, the shortwave that eventually produces the big storm is entering the US from southern California, the Baja of NW Mexico, and Arizona.
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March 23, 1983, the shortwave that would set off a major early spring snowstorm in NC which dumped up to 10" of snow in Lumberton, NC enters the US through California a few days prior to the storm.
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January 5, 1988, immediately preceding the huge/infamous overrunning event from Texas and Oklahoma to the Carolinas, the s/w which eventually results in a winter storm over the SE US is entering the US from California and there's a big vortex over SE Canada.
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The shortwave that immediately preceded the March 1993 Superstorm which produced blizzard conditions from southern Alabama to the Canadian border, is entering the US stage left through California on March 10th w/ a healthy vortex over the Great Lakes
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December 31, 2001 preceding a big board wide event on January 1-3 2002, the shortwave which eventually led to a big winter storm in the SE US is entering the US thru California and Nevada and there's a big vortex over SE Canada
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Immediately preceding the February 12-13 2010 event which led to a big snowstorm from Texas to North Carolina, the shortwave which accompanied this storm entered south-central California on February 10th.
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January 7, 2011, the shortwave that helped kick off the amazing winter storm that would come a few days later is entering the contiguous US through southern California.
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