Heading Toward A “Warm Nights” Record; Warming Summers Too

September 18, 2014

BMAC 60 Degree Nights

The 61 degree low at PDX this morning was the 43rd morning this warm season when the temperature didn’t drop below 60 degrees.  The all-time record of 44 days was set just last summer.  If we have two more 60 degree mornings, we’ll set a new record.

It is important to point out that technically the low temperature records are for the calendar day…from midnight to midnight. For example, if it’s 62 in the morning, but then that evening cooler air pushes in with a 58 at 11:59pm, the low for the day is the 58 and it wouldn’t count in the graphic above.

And yes, Portland metro area nights are getting warmer and warmer aren’t they?  Here’s an updated look at 60 degree nights at PDX over the past 70+ years


Much of this is due to the Urban Heat Island effect…as cities grow they turn warmer.

But are our summers getting warmer? The short answer is YES.

To eliminate most of the urban heat island effects, you can average all stations in NCDC Climate Division 2 in Oregon.  That’s the Willamette Valley (and foothills) stations.  There’s a slow warming since 1950 during the 3 month period June-August. jun-augdiv2temp

Note that from the late 60s to early 80s there was a flattening or even cooling trend in there.

As I noted a year or two ago in this blog, the July-September warming is more significant (summers are hanging on longer?). In fact the only significant change in temperature in the lowlands for the past 30 years has been a cooling in the late spring and warming in the late summer.  Here is the spring chart


and the July-September chart


Winter and fall haven’t seen much of any change. In fact I noticed the Cascades have seen just about NO change in the winter months.  Keep all these numbers in mind when people argue with you one way or another over Global Warming.  Not quite as clear-cut as some would have you believe!

Chief Meteorologist Mark Nelsen