Tuesday, September 9, 2014

Did "THE BLOB" cause our warm summer?

This has been an unusually warm summer here in the Pacific Northwest.  But why?

Several people have suggested the cause is a pool of unusually warm water over the northeast Pacific, one my colleague Nick Bond has amusingly  termed "the blob."   How did this blob develop and what are the implications?

As noted above, the blob is a region of unusually warm water off the Northwest coast.  Here is the difference from normal sea surface temperature (the SST anomaly) for this summer (courtesy of NOAA).  Can you see the orange area off our coast, that is the "blob".  It represents an area of water about 2-3 C warmer than normal.

The blob developed last fall and early winter, as illustrated by the sea surface temperature anomaly maps for September 26, 2013 and January 23, 2014, shown below.

But why?

The warm blob developed last winter as a result of the unusual persistence of high pressure over the eastern Pacific.  Here is difference from normal for sea level pressure for Sept to December 2013.  WOW!   A huge anomaly with the pressure over the northeast Pacific being over 6 millibars (aka hPa) above normal.  Folks, that is a big anomaly.  And it was associated with our dry fall and early winter last year.
Nick has analyzed the impacts of this high pressure area; one associated with far less storminess than normal (storms are generally associated with low pressure regions).  With less storminess, there were fewer waves and less mixing of the upper Pacific, mixing that tends to bring up colder water from beneath the surface.   Thus, the surface layer of the ocean ended up several degrees warmer than normal and this anomaly persisted into the spring and summer.

So now you know the origin of the blob: the impact of unusual fall high pressure.  But how does that warm the air over us?

During the summer, the East Pacific High builds northward in the eastern Pacific and the air that reaches us on the typical summer day comes off the Pacific.  To prove this, here is the trajectory of air ending over Seattle on August 29th.  It was over the blob a few days earlier!

The temperature of the low-level air is greatly influenced by the sea surface temperature and thus warmer water tends to cause the air reaching us to warm.    The temperature anomaly of the blog is 2-3C (roughly 4-5F) , which is quite similar to the degree of warming above normal this summer over much of the Northwest (see graphic)

A number of you have complained about the humidity being unusually high this summer.  Blame the blob.  Warmer air can acquire more water vapor than cooler air and the amount of water vapor air can hold increases VERY rapidly with temperature.

There is, of course, a lot of interest in whether the warm temperatures this summer were associated with global warming.   It does not appear so.  The warming was caused by anomalous high pressure over the eastern Pacific last fall and there is no reason to believe that has anything to do with warming the planet from the greenhouse gases mankind emits.

One final note:  the persistent warm air was a bonanza for extended range weather forecasters.   With the warm water holding in place, our long-range computer models, such as the Climate Forecast System (CFS) accurately predicted the warm summer months earlier.  Don't believe me?  Here is the proof: the June-July-August surface temperature anomaly forecast made in March!  The reds are 1-2 C warmer than normal.  Impressive skill.


JewelyaZ said...

So, Cliff, when is something going to come "eat" the Blob? Are we going to have another fall/winter with it, or will it break up/dissipate allowing us to have more normal conditions this year? I'm hoping for rain rain rain rain here all the way down through California... not because it's fun, but because like our green beans, it's good for us. :-)

Unknown said...

I was also wondering if the "blob" will persist and how it might affect this Fall and Winter.

rsktkr said...

That's a good question.....is that blob gone or is it going to impact this fall/winter season again? If it's going to stay is it warmer or cooler than last year?

Dele said...

So, my question is why the High Pressure Anomaly and how / why did it develop?

Ansel said...

How does the "blob" relate to the PDO? Is this a shift back to the warm phase of the PDO? If I am correct we are talking about the same piece of ocean.

I went on a cruise to Desolation Sound in mid-August. The SST there was about 70 F. You can actually go swimming! But that is, I am told, normal there because there isn't much mixing.

Dan said...

I'm just glad that our dewpoints are back down in the 30s. Blob or no blob, it seems that the reduced insolation has finally broken the back of our humid streak.

caveat emptor said...

Is the warm blob going to kill the ski season this winter?

AnneScott said...

Don't our warmest days in summer come during offshore flow with a continental air mass coming over the Cascades? Also storms feed off of warmer water so would that mean that storms moving across the Pacific (once the Westerlies get active) would strengthen when they pass over the "blob"?

Rex Block said...

Sorry, but I have to disagree. In the mid latitudes, the atmosphere forces the ocean, not the other way around. As you correctly point out, the positive SST anomaly was caused by the lack of mixing from storms. But the feedback of the ocean to the atmosphere is small. This is still cold water (about 65F), just not as cold as normal.

Take a look at the 300mb, 500mb, and 500mb anomalies for July and august. Large positive anomaly over the northwest. I don't think a positive SST anomaly in the mid latitudes could cause this. To me, the ridge aloft caused our warm summer. The SST is a result of the lack of storms, not the cause of the warming. Just my opinion.

Dean said...

While I can accept the idea that a warm anomaly off the coast can warm nighttime temps, I have a hard time believing that water that is in the mid-60s has anything to do with higher daytime temps.

Every time a marine push develops shows that.

Unknown said...

Hey, looking at picture from September and the new one, looks like a trail from fukushima. is it related?

Sarah Cassway said...

Many articles that I have read expressed how the "Blob" was not created by climate change. Do you believe this, or do you think that the"Blob" came out of no where.

johnhilton said...

There is a theory that some of the anomalies, like much longer than normal standing weather patterns and maybe the blob, are being caused by the radically decreased temperature differential between the equator and the North Pole. The equator hasn't heated up that much but the North Pole is heating up fast. That temperature differential used to keep things like the jet stream in a tighter pattern, but now that the differential is less, there are wild swings and these more exaggerated patterns get locked into place for longer. There are analogies for this. If the theory is true, the blob may have everything to do with temperature change (climate change).

Unknown said...

"There is a theory that some of the anomalies, like much longer than normal standing weather patterns and maybe the blob, are being caused by the radically decreased temperature differential between the equator and the North Pole."

Except the North Atlantic has a cold anomaly - the tale of two extremes.

Since the Pacific and the Atlantic oceans communicate via the North Pole maybe it's the missing heat from the North Atlantic :).