Temperatures as we hit the halfway mark for March are three tenths of a degree above average. They won't stay there as the next ten days do generally average out to cooler than normal for Philadelphia. We're not talking brutal, arctic, apocalyptic cold for us in Philly or in the Mid Atlantic.
It will, however, be cold across the Plains and across the Midwest. By March standards, a pretty decent round of chill will drop across these areas as temperatures could average 10 to 15 degrees colder than normal between next weekend and the middle of the week preceding Easter. The GFS and Euro support each other in showing the potential for a cold run across the nation's center.
The West is poised to be rather mild, as early season warmth continues to spring forth across California and Nevada. This pattern was already getting established with a mild run the past couple of days. Denver set a record high with 76 degrees yesterday (just a week after getting soccer match postponing snowfall), with Phoenix tying a record at 92 degrees yesterday as well. The warmth stays west of the Continental Divide while the rest of the country gets varied states of chill over the next week or two.
The cause of this is a strong arctic blocking regime (-AO pattern) that is allowing colder air to ooze southward from northern parts of Canada and the Arctic.
March may end up below average for temperature in Philadelphia, which would be the first time since December 2010 and January 2011 where we have had consecutive months of below average temperatures here in the city.