Monday, December 10, 2012

The Most Common Winter Temperatures

December, January, and February make up the months of meteorological winter...they are the three coldest months on average regarding temperature for almost everyone in the US.  In Philadelphia, the 140 years of daily climate data that we have means there's a lot of information about the most common high temperature ranges and low temperature ranges in the city.

It's rare to get real, true, arctic cold air in our region.  We've only had 64 days since 1872 where the high for the day didn't break 15 degrees.  In many cases, arctic air gets modified as it approaches us thanks either to a lack of snow cover over us, increasing strength of the sun at our relatively lower latitude, the Great Lakes, or any number of other factors.  It's rare to have the cold that's more common with Minnesota or farther north in Upstate New York.

The most common high temperature range is in the 41-45 range, with 19.7 percent of all winter days featuring highs in that range.  Including the 36-40 range, nearly 39 percent of winter days feature highs in this ten degree range.

Low temperatures typically average out to the temperature range near freezing -- from 26 to 35.   Over 42 percent of all winter days are in that ten degree swath of real estate.  Going back to the arctic point I made earlier, we've only had 45 nights since 1872 where the low in Philadelphia went to 0 or below and only 179 nights all time where the low has dropped below 5.

Even with our warmer stretch of winters of late and with the influence of the urban heat island, getting overly warm overnight lows has been a pretty rare occurrence.  Low temperatures over 51 degrees have occurred just 61 times all time in Philadelphia, with no night warmer than 60 (January 9th, 1998) in Philadelphia's winter weather history.