I have been watching Northwest weather for a long time and I have never seen anything like what we have experienced during the last month:
An extended and intense minimum temperature heat wave.
Something amazing has been going on this fall, and for some reason the Ebola-crazed media hasn't picked up on it. But that is why we have blogs. Gardeners know something weird is happening. Vegetable plants are not dying. Tomatoes are still ripening.
There are movies about this issue.
Here are the temperatures at Seattle-Tacoma Airport during the past 4 weeks, with the average high (red) and lows (blue) shown. Only ONE day in that entire period has seen the temperature dropping to the average low. For most days, our minimum temperatures have been 5-10 degrees above normal. Our minimum temperatures last night were close to the average maximum for the date!
And this is not Seattle alone, here is the same trace for Bellingham. Same thing. Bellingham cooled to 59F last night!
A close-up over Washington State shows some areas are 8-10F above normal.
And the latest NOAA Climate Prediction Center extended forecasts show no end in sight
to the warmth:
Now why is this happening? This is an important question because one can expect some folks in the media and advocacy groups to start saying this is a "sign" or "consistent with" global warming due to mankind's emissions of greenhouse gases. There is no reason to think that is true.
There are two main reasons for the warmth and they are both associated with the anomalous atmospheric circulations we are having.
Reason #1: a persistent area of low pressure over the eastern Pacific. The figure below shows the sea level pressure anomaly (difference from normal) for the past month. There is an area west of us with pressures well below normal. Such anomalous low pressure is associated with stronger than normal southerly and southwesterly winds over us that blow in warmer than normal air.
This is probably the major cause. Then there is something else, something I have talked about in previous blog: the warm water BLOB off the coast.
Below is the sea surface temperature anomaly map for the past week. You see the orange and red colors off the coast that indicate temperatures 2-4F above normal? The BLOB still lives. So air passing over the eastern Pacific is exposed to warmer than normal water. Me like BLOB, BLOB is good.
As I noted earlier, the BLOB has little to do with global warming but was produced by anomalous high pressure over the Pacific last winter and year.
So our ridiculously warm temperatures this fall are being produced by an unusual combination of high pressure a year ago that produced the blob and low pressure this fall that is bringing up warm air from the south.
There is no reason to think that these circulation anomalies are caused by human greenhouse gas emissions. And remember that the eastern U.S. has been colder than normal.
Well, time for me to go out to my garden to harvest some more red tomatoes.