As scripted by the consensus of the seasonal outlooks, the winter got off to a cold start. In Philadelphia December snapped a nine-month warm streak.
Officially, the Philadelphia last month's temperature came in at 32.7, or 4.7 degrees below normal, making it the coldest December since 2000, more reminiscent of the Decembers in the chilly 1960s.
The outlooks relied heavily on the strong La Nina, the unusual cooling of surface waters in the equatorial Pacific, which is expected to persist through the winter.
Based largely on that La Nina, the aformentioned consensus foresaw a warm-up after December, and as if on cue, the first two days of January felt suspiciously like March.
However, that warm-up is over, and it appears that cold will persist at least into next week, with a snow threat toward the weekend.
This may sound annoyingly familiar, but the European computer model sees a possible snowstorm that others don't. For now, the National Weather Service is listing a generic 30 percent chance of snow for Friday and Saturday.
We can predict only that various scenarios will gain computer favor during the next few days, so don't worry about the supply inventory until at least Wednesday.
In the meantime, almost in defiance of La Nina, the cold will persist.
Before this year, Philadelphia had never recorded a 10-plus inch snowfall during a strong La Nina at least since 1950. Last month was the coldest December during a strong La Nina since 1955.
During the next few weeks, either La Nina will rout the cold or we'll all re-learn that the atmosphere is a complicated place.