The oddly warm PDX Winter of 2012, and some historical notes.

We're now in Winter, but some trees still have their leaves!  I've also learned that, when maple and pear trees shed their leaves late, they don't show any red or orange; they turn yellow and brown.

Just as odd, this weekend will be the first below-freezing temperatures in Portland, since last Winter!

I thought it worth grabbing some NOAA climate data from PDX airport (records go back to October 1940), of extreme low cold snaps.

Lows of 32º F or less:

• 38 days Jan. 1-Feb 7, 1949
• 25 Dec 9-Jan 2, 1985-86
• 20 Dec. 24-Jan 12, 1978-79
• 17 Jan. 14-30, 1957
• 15 Jan. 22-Feb 5, 1985
• 15 Jan. 23-Feb 6, 1950

Lows of 20º F or less:

• 9 days Jan. 27-Feb. 4, 1950
• 7 Dec. 19-25, 1990
• 7 Dec. 7-13, 1972
• 7 Jan. 24-30, 1957
• 7 Jan. 13-19, 1950

Lows of 10º F or less:

• 7 days Jan. 28-Feb. 3, 1950
• 3 Jan. 26-28, 1957
• 2 Dec 30-31, 1968
• 2 Dec 16-17, 1964
• 2 Jan. 16-17, 1950
• 2 Jan. 23-24, 1943

Lows of 0º F or less:

• 1 Feb.2, 1950
• 1 Jan 31, 1950

Notice something?  The colder the cold snap, the less often it has occurred in the last 36 years (last 36 years highlighted in orange), compared to the previous 36 years (for comparison, I divided the total years of records at PDX airport in half).  Not a single cold snap in over 20 years, as a matter of fact.

One last thing: PDX Airport Heating Degree Days.  In the previous century it (in conjunction with Cooling Degree Days) was used a great deal to compare the heating and cooling needs for different climates.  Now however, we can use it to peek at climate change, and see if there are any long-term trends.  The Heating Degree Day is the mean daily temperature, subtracted from the baseline of 65 degrees; negative numbers are simply discarded. For an entire season, you add up each day's degree days; the higher the number, the cooler the season is.

It has been getting warmer over the last 70 years, as you can see by the trend line (dashed green).