So many variables … even the “official” temps can vary by 10 or 12 degrees depending on which authority is making the report.
So far as I’m concerned a 20 or 30 year moving average is not what I want to look at–I want the records since 1887 (or whatever year they go back to in a given town).
As I posted on another thread, we’ve been on the edge of z.7 in zone 6 some 60 years ago, and and back there now after being in z. 5 for several years. I’d rather have the 130 year minimums and maximums rather than the 30 year set.
Somerset KY had -29 in 1960, -28 in 1963, -31 in 1977, -31 1985, and -32 in 1994 for an all time low since anyone had a thermometer. (Yet -32 is what the local newspaper printed, but -20 was what the national weatehr service had for 1-19-1994.
And since Lake Cumberland was impounded in 1950, only 1977 and 1978 did it ice completely over. January 1977 was and is the all time record cold month for Somerset, KY…with 21 days going below zero.
On the high side…Somerset had highs of 104 in 1980 and 2007…for the record.
London had 105 in 2012 for the record.
Morehead and Henderson KY had their all time record highs in 1936.
Some other towns, including Mt. Vernon in 1952.
We had a spell in the 1930’s of temperatures being hot.
We had a spell from 1960 through about 1985 with very low winter temps.
From 1997 to about 2016 we have had a warm spell. Last 4 years we’ve had lower than average summer highs and higher than average winter low’s.
If you throw out the old records and go with 30 years only…1994 was the coldest and we appear to be in a warming trend. And with 2007, 2008 and 2012 setting some all time highs, we appear to have peaked and be on a cooling trend.
So, I still think the 130 year highs and lows are more apt to tell me if a tender plant will likely make it in the long term.