(Bloomberg View) — As the snow piles up toward record heights inBoston, San Francisco is going through an extraordinary dry spell —this was the first January in 165 years in which the city recordedno rain at all. As another snowstorm keeps schoolkids home in theSoutheast, flowers are blossoming in the Pacific Northwest, wheretemperatures in February have been above 60 degrees.

Yet this is not as contradictory as it sounds — just theopposite. This kind of winter doesn't happen every year(obviously), but the divergence reflects a weather syndrome longfamiliar to forecasters, borne of climate conditions originatingover the Pacific Ocean.

Scientists view this weather — especially what's happened inFebruary — as the outgrowth of two so-called teleconnectionpatterns. One is the Pacific North American pattern, in which highpressure persists over Hawaii and the mountain West, while lowpressure prevails over the Aleutian Islands and the Great Lakes.The jet stream spools around these pressure zones, rising northwardover the West Coast (drawing warm air up) and dipping southwardthrough the center of the U.S. (pulling arctic air down). Once inplace, this pattern can last weeks. In the winter of 1976-77, a PNAkept going for four months, relentlessly holding the eastern halfof the U.S. in the freezer, and keeping the West warm and dry.