Sunday, October 27, 2013

Putting October Chill Into Perspective

The couple of mornings with lows below 40 degrees (Friday and Saturday both dropping to 37) have brought the first suburban frosts and freezes and have brought us our coldest mornings since April. October does this -- we have had lows below 40 on 28 occasions since 2003.

The list on the left shows those October lows, excluding yesterday, that are below 40 degrees. With the exception of 2010, we've been here, done that, each...and every...October. Some years, like 2006, had it happen quite a bit more frequently while others had it happen once or twice.

Getting into the 30's on a few occasions is not going to help determine a cold winter or a cold month. Heck, even frequent cold shots like October 2006's didn't fully drive the bus on the following winter, which featured a very warm first six weeks before the bottom dropped out finally on temperatures in late January. That said, monthly temperatures in October normally do matter on the whole.

You may recall our post from a couple of weeks ago about this -- the warmer the temperature (or colder) for Philadelphia, typically the stronger the correlation in the following winter towards warmer or colder temperatures on the whole. In fact, if temperatures fall into the warmer or colder thirds, the correlation runs at around a 70 percent clip for the following winter.

Temperatures this October will slide into the warmer third of what we have seen since 1940 -- perhaps near top 15 warmest since records were first kept in the 1870's. The historic tendency is warmth in October more often than not yields warmth in winter (and the same with cold).

That said, it can (and does) get chilly occasionally, even in warm months in October, but a few colder mornings themselves don't an October make...nor also provide a true indication of what's to come.