The warming causes convection in one of the world's most-sensitive weather regions, disrupting patterns all over the planet.
Typically, one by-product is an energized southern branch of jet stream winds, which translates to an active, juicy storm track across the southern United States.
In some years, that results in strong coastal storms, and if they are able to interact with cold air to the north, expect a 100 percent chance of empty supermarket shelves.
A strong El Niño, combined with a persistent blocking pattern that supplied cold air to the region, contributed to the wintry harvest of the 2009-10 winter, the snowiest on record in Philadelphia.
A few caveats are worth mentioning.
Some El Niño winters have been snow duds, including the 1997-98 season, when less than an inch was recorded officially in Philadelphia, and 1972-73, the only winter without measurable snow.
And, as we all know by now, the seasonal-forecasting limb is a tenuous one.
Accu-Weather's 2011-12 winter forecast is one the company wishes would go away. It saw a tough winter for much of the nation. "Accu-Weather's long-range experts agree that the Midwest and Great Lakes region will be dealt the worst of winter this year," it said in its October release.
The Midwest had its second-warmest winter in the period of record, dating to 1880; in the upper Great Lakes region it was No. 3.
The summer outlook fared better. Accu-Weather was on the case for heat in the Rockies and Plains, but it also said that Philly, New York, and Washington would have near-normal temperatures with "a lack of prolonged heat."
In Philadelphia, this is about to become one of the 10 hottest summers ever, even though the rest of the month may be relatively 90s-free.
In the meantime, you should have plenty of time to make your winter preparations. The earliest measurable snow in Philadelphia occurred on Oct. 10, 1979.
Contact Anthony R. Wood at 610-313-8210 or firstname.lastname@example.org