Autumn Starts Today Following the Driest and Warmest in Seattle Records

Autumn started today at 1:02 PM, with night and day being equal; thus it is given the name autumnal equinox.   The other neat thing about today is that the border between day and night, called the terminator, is oriented exactly north-south, as seen in the following visible satellite image:

As suggested in my previous blog, this is a summer for the record books.    As shown by a table prepared by the Seattle National Weather Service forecast office, Seattle-Tacoma Airport had the driest summer on record, with only .52 inches.    This table has an issue...they combine the downtown Seattle and Sea-Tac records (Sea Tac only goes to 1945), which is really a problem since the precipitation climatology of the two is different.  As shown in my previous blog, the lowest previous summer precipitation at Sea-Tac was 1.28 inches, making this years record even more impressive.

The summer was also very warm, and we tied the record for average summer high with 78.6F.

Really quite an amazing year, with the wettest winter on record and the driest summer on record.  Both were due to persistent upper atmospheric flow anomalies (differences from climatology).  This summer a persistent ridge of high pressure was parked over us, with a trough of low pressure over the eastern U.S.  They were unusually cold and wet, we were unusually warm and dry.  

Why such anomalies?   We don't know.   Could be typical chaotic behavior of the atmosphere.  At this point, there is no reason to believe such patterns are associated with global warming--climate models forced by increasing greenhouse gases don't produce them.  

Our feathered friends know the season is turning, with a massive southward migration going on.  How do I know. Weather radar!

Here is the radar image from 11:03 PDT last night.  Lots of echo..but no rain.  Those are birds.  How can I be sure?  There was no echo before sunset and then the radar let up as it got dark.  Lots of birds prefer to fly after dark.  Probably safer for them (predators can't see them well) and perhaps they use the stars for navigation.

Weather radar even tell us which direction the birds are flying using the Doppler velocity output. Here is the Doppler Velocity at roughly the same time using the Camano Island radar.  It tells you the component of motion towards or away from the radar.  Cold colors (like blue) indicate incoming, warm colors (orange/yellow) for outgoing.   Clearly, our feathered friends are heading south.

from Cliff Mass Weather and Climate Blog http://ift.tt/2yjrSou