Chill in perspective

As John Bolaris posted Monday morning, a very big chill is on the way after the rain stops, and for this time of year, it might reach historic proportions.

The National Weather Service is forecasting a low of 20 for Wednesday morning at Philadelphia International Airport, which would tie the record.

But we are more impressed with just how cold the rest of the day is going to be.

Even if the overnight low misses the record by a degree or even two, with a forecast high of freezing, Wednesday is poised to set a record for the lowest daily average temperature for a Nov. 19.

The reigning standard is 28, set in 1936. Should the forecast a low of 20 and a high of 32 work out, the  daily average would come in at 26 on Wednesday.

It is almost certain to finish in the top three in the period of temperature record, which starts in 1874.

After 1936 come the pretenders – 30.5 in 1951, and two others tied at 31.

The record-low maximum for a Nov. 19 is 35, set in 1951, and that one looks to be in serious trouble.

While 140 years represents one of the nation's deepest climate archives, the daily records have a certain non-linear quality that likely would smooth out if the dataset were more extensive.

For example, the record-low daily maximum and average temperature for a Nov. 15 – 31 and 25.5, respectively, set  in 1933 – is lower than the one for Nov. 19.

On Nov. 15, 1933, during a nasty four-day cold outbreak, 0.2 inches of snow fell officially in Philadelphia.

In 1989, 4.6 inches of snow fell on Thanksgiving eve, Nov. 22, and during the early morning hours of Thanksgiving, crowning a four-day cold snap.

Nothing like that is in the forecast this time around; just a taste of January.

Incidentally, based on the forecast, Wednesday would be the coldest day since March 4, when the high didn't get past 29.