Why it's not snowing here

As we've mentioned in previous posts, snow is a capricious phenomenon that in some winters just doesn't want to fall around here, not that everyone is complaining.

In the period of record, total seasonal snowfall in Philadelphia has finished in the single digits 20 times, with this season, currently at 5.2, making a serious run at 21.

Last winter, locals will recall, Philadelphia was having a southern New England experience, as storm after storm seemed to target the official measuring station.

This winter the big factor has been in the predominant type of storm delivering snow to the Northeast.

The ones that have creamed parts of New England and snubbed this area, including the historic bust of two weeks ago, have been so-called Miller Type-Bs, named for a meteorologist who developed the classification system in the 1940s.

The Type Bs evidently have something to do with the uniqueness of the topography of the East.

Those are storms that swing by from the Ohio Valley, fall apart in the Appalachians, but then redevelop along the coast, somewhere between the Carolinas and New England. They can be forecasting nightmares, since they are virtual concepts until they blow up.

The heaviest snows typically are thrown back well northwest of the storm's center, so the farther north  and east that a storm intensifies, the less snow falls in Philadelphia.

Can you guess what has been happening this season?

By contrast, "Miller Type-A" storms develop more tidily, migrating from the Gulf Coast or forming off the Southeast Coast. The March 1993 blizzard and the Jan. 7-8, 1996, mega-storms come to mind. Not that those storms are challenge-free.

The classification system was the work of James E. Miller, a New York University researcher who published his paper in the journal Meteorology in 1946.

In his paper, Miller noted that the Type-B storm (he didn't call it a "Miller Type-B," by the way; others did that), might be tied to the "peculiar topography" of the East.

In a 10-year study, Miller determined that the Type-B dominated in January and February.  In January, only 25 of 34 coastal storms were of Type B, and 17 of 28 in February. The caveat, of course, is the sample size.

Based on the forecasts, at least two more Miller Bs are on the horizon on Thursday and again on Saturday.

About the only thing to expect with any certainty will be frequent changes to forecasts, and don't be shocked if the snow drought continues.