Thursday, October 10, 2013

Paradox Day

October 10th brings two milestones of direct opposites in weather to Philadelphia.  It's one of those few dates on the calendar (along with a couple of dates in April) where one can get snow...or heat...depending on the pattern that's overhead.

First, the earliest measurable snowfall...occurring on this date in 1979.  This rare snowfall brought a couple of inches of accumulation (that didn't last long on the ground) to Philadelphia and the western suburbs, with Wayne picking up three inches of accumulation from the season's first snow.  This snowfall brought coatings to an inch or two of slush to many along the coast and just west, with higher elevations picking up a few inches of accumulation. Some mountainous areas of Virginia and West Virginia picked up over six inches of snow from this event. It even snowed that morning prior to Game 1 of the '79 World Series in Baltimore.

Snowfall distribution -- via Kocin/Uccellini snowstorm book
"Northeast Snowstorms"
October 10th brings our latest 90 degree day on record as well -- happening in 1939 (forty years prior to the October '79 snowfall). The 1939 heat event brought record highs to many locations throughout the Northeast, with mid and upper 80's common in many spots on that date. Central Park also hit 91 on that date in October.

An interesting stat is that the proceeding winter after the latest 90 degree day generated more snowfall (22.3") than the one with the earliest snowfall (20.9"), along with slightly colder temperatures as the winter of 1939-1940 averaged out about a degree colder than the winter of '79-'80. It's another log on the fire against wanting snow in October around here...our track record of winter performance with such early snows is not the greatest.

Warm days can still continue through much of October, along with snow chances. But this date is, along with April 7th, 8th, and 12th in the early half of April, among the precious few where Philadelphia has experienced snow...and heat...just not in the same year, thankfully.