Why Are All Snowstorms on Weekends?

UPDATE: NBC-Philadelphia has run a check of all major snowstoms in Philly and says that 77% occurred on weekends (as defined as a range of days that includes the weekend).

This graphic is a gross oversimplification of our snow storms this season, but it does point out something interesting -- this weekend's expected big snow storm in the mid-Atlantic is the third in a row falling on a Saturday.

(This weekend's storm may begin Friday afternoon, a little earlier than the previous two. As the graphic notes, there was another possible storm for Tuesday but the models seem to be losing that one as of this morning.)

Is there anything to this trend? Probably not. Things like air mass thunderstorms which don't involve "synoptic" weather systems moving across the nation can decrease on weekends because of pollution, but this would seem to be just a coincidence. It takes about a week for a storm to move from the West Coast to the East during the winter, so it's not unusual for the days to correspond (but for two months as we have here? who knows, nobody keeps records of this stuff).

I looked back at some radar loops and here's a list of the major storms (rain or snow in the mid-Atlantic) since December 2nd (which was a Wednesday storm). Mathematically, the period Thursday-Sunday represents 57% of the week, so you would expect to see a percentage of storms near that, but as you can see below, 11 of the 12 storms (92%) were in this period. Weird.

Saturday Dec. 5 - Mostly RainTuesday, December 8th - New England SnowstormSunday Dec. 13 - Mostly RainSaturday, December 19th - mid-Atlantic BlizzardFriday Dec. 25 - Mostly RainThursday Dec. 31 - Mostly RainThursday Jan. 7 - Mostly RainSunday Jan. 17 - Mostly RainThursday Jan. 21 - Mostly RainSunday Jan. 24 - Mostly RainSaturday, Jan. 30th - mid-Atlantic Snow StormSaturday, Feb. 6 - Another mid-Atlantic Snow Storm?