March 29, 2015

Will This Summer Be Warmer Than Normal?

I believe the probability of a warm summer in the Pacific Northwest is quite high.

Let me tell you why.

During the summer, high pressure builds offshore (the East Pacific High) and marine air from off the eastern Pacific Ocean slowly moves into the Pacific Northwest.  The temperature of the ocean surface is an important factor in controlling our surface air temperature (and dew point).

For many months, the sea surface temperature (SST)  of the eastern Pacific has been above normal and that is certainly true today.  Here is the sea surface temperature anomaly (difference from normal) for the past week.  You can see a huge area of warm water off the west coast of North America, with the water temperatures being 3-3.5 C  (5-6F) above normal.  There is no reason to suspect this warm water anomaly won't persist into the summer, and as the air moves over the warm water its temperaturs will be enhanced.

In fact, the latest runs of the NOAA Climate Forecast System (CFS) model suggests a continuation of the warm water off our coast into the summer.
Interestingly, if one plots the departure from normal of the Seattle temperatures for the last year one finds that nearly every day has been above normal (see below), with an average departure from normal of about 2C (3.6F), which is roughly the value of the sea surface temperature warming off our coast.  Really amazing how consistently warmer than normal we have been.

So the existence of the warm water alone suggests a warmer than normal summer.

But what does the NOAA CFS forecast for summer air temperatures look like?  Here is the answer for June-July and August.   Substantially warmer than normal!
But why depend on one seasonal forecasting system?   There is an International Multi-Model Ensemble (IMME) that combines the seasonal forecasts of the U.S. (NCEP), MeteoFrance, the European Center and the UKMET Office.   Here is the surface temperature anomaly forecast for the same period for IMME.  You guessed it....warmer than normal summer in our area.

The official NOAA seasonal  temperature probability forecast?  Warmer than normal over the Northwest, of course.

Seasonal forecasts have an imperfect track record, with some major busts in recent memory.  But making use of all the tools my profession has available, it does appear that the probabilities are strongly weighted towards another warm summer here in the Pacific Northwest.  I haven't discussed precipitation , but similar guidance does not suggest an usually wet or dry warm season.

What are the implications of the upcoming warm summer?  A longer hiking season for sure.  Increased chances of wildfires.  Higher summer humidity. A better beach season than normal. Another great tomato growing season.  Less chance of spring freezes in eastern Washington. And much more.  I enjoy a warmer summer even though it may not be politically correct to say it.


  1. I notice the projected warming along the equator all the way to South America, typical of an El NiƱo year, which this is projected to be, but I don't see any evidence of it yet in the Pacific sea surface temperature map above it. I'll be watching to see if it actually happens . . .

  2. Is there a URL for the ensemble seasonal forecast? Sorry if this is a duplicate comment...

  3. Cliff, even though the increase in average temperature tracking, more or less, with sea temperature seems rational, nevertheless, seeing the data support that mental construct is a nice dovetail of science and street guy thinking.


  4. Sorry to double up on your blog, but I noted this morning, and neglected to mention in previous post, that the NWS forecast for the week has temperatures cooling and the snow level falling to 2,500 to 3,000 feet. I like that while temperatures on average are warmer, and the prediction for the summer as well, the atmosphere is stockpiling a little more snow in the mountains for water in our reservoirs, which, apparently, we'll need.

  5. Hi Cliff,
    I agree with your assessment based on your data, however, I would caution you in regards to the SEA temperature data. As you show in your graph, the mean temperature deviation is around 2 degrees C. I am within two NW miles of the airport at pretty much the same elevation. My thermometers read 3 to 5 degrees cooler on a regular basis, including Max temps. As you know, I have been a professional weather observer for nearly 4 decades, so I know what I am talking about. There is a problem with SEA's ASOS temps. I believe it has to do with proximity to the runways and heat island effect. That being said, your 2 degrees C deviation falls within that error margin. Just some food for thought my friend. Take Care, Randy Cryer

  6. Is there any way to generally estimate what effect the warm water (and/or resulting air-temp modification) may have on high pressure systems, ridges, or fronts during our summer months? Or are these synoptic-scale phenomena too dominated by upper-atmospheric movements to be disrupted by surface-level temperature modification?

  7. Dear Dr Mass,

    Why/how do you predict higher summer humidity in your conclusion above? Does it have something to do with the air coming across the warmer water?

    Thanks for your insightful musings.


  8. For the moment, we seem to be back to normal.

    Cliff, I have notice that for several years at least, there seems to be a cold spell every year about the first week of April. This year seems to be following suit... Do your data bear this out? Or am I looking too short-term?

  9. Bring it on! I have a higher melt point than most folks in Western Washington! I thrive between 75 and 90 degrees F.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

The Snow has Arrived and Much More is on the Way

This afternoon I biked home in light snow and it was magical.   And the Northwest will enjoy a lot of snowflake magic during the next week. ...