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A strong El Nino is brewing in the Pacific Ocean, the waters off of the western coast of the United States remain warm (positive Pacific Decadal Oscillation) and October Siberian snowfall is currently running a bit above normal. How much snow can the Washington Area expect this Winter?
This is a very tough winter forecast as strong El Nino winters in the past have produced either very wet or very snowy conditions in the Mid-Atlantic.
The key will be the behavior of the Arctic Oscillation (AO) and whether or not it can go into its negative phase which would allow cold air to infiltrate the eastern United States from Canada.
The arguments for above normal snowfall:
Siberian snowfall in October is currently off to a healthy start: there is a fairly strong correlation with colder temperatures during winter occurring in the eastern United States following above normal Siberian snowfall in October.
While the current Siberian snowfall is not off the charts, it is at least a bit above the seasonal average and that may bode well for some cold shots moving into the eastern United States during the upcoming winter.
The Pacific Decadal Oscillation remains in its warm (or positive) phase: Just like last year, warm water is parked along the southern coast of Alaska and continuing southward along the Pacific northwest coast of the United States. This should favor more ridging off of the west coast of North America and if these warmer waters hold, could allow shots of colder air to infiltrate the eastern half of the nation.
El Nino is forecasted to weaken during the second half of winter: Winter may very well start off milder than average in December with very little cold air to work with through mid January. As El Nino begins to weaken during the second half of winter, colder air may begin to infiltrate the eastern half of the nation increasing the prospects of several good snow storms.
Let’s take a look at temperature and precipitation trends based on the analogs from previous strong to moderate El Nino winters with a Positive PDO:
Upcoming Winter Forecast for Midwest, Mid-Atlantic and New England:
Winter may start out milder than average continuing through January but as El Nino begins to weaken, colder air may become entrenched in the eastern half of the nation from mid/late January through early March.
The forecast is extremely tricky this year because previous strong El Nino winters have produced wild swings in snowfall totals from very little (1997-98) to above average (1957-58, 1982-83, 1986-87).
The behavior of the NAO (North Atlantic Oscillation) and Arctic Oscillation (AO) can’t be predicted more than about 2 weeks out and will dictate whether precipitation falls mainly as rain or snow this winter.
According to the analogs that I chose, temperatures in DC should run near to slightly below average and precipitation should be above average.