In message ,
Scott W writes
After being reminded about this a couple of weeks ago I decided to have
a look at the stats back to 1806 and see what the results are.

If there is a run of cold days (3.3C or less) around mid-month the
chance of an average to colder than average January and February is 94%
and 74% respectively. The chance of an average to colder than average
March is 96%. Also notable is that the chance of a severe spell in
January (4C colder than normal) is 30%.

The full blog post can be found here. http://wp.me/p2VSmb-wO

Those are remarkably high percentages. The biggest surprise is that it
should be such a strong pointer for as far ahead as March, and - oddly -
stronger than for February.
--
I'm not paid to implement the recognition of irony.
(Taken, with the author's permission, from a LiveJournal
post)