Regime Change – San Jose

I was looking at the cold and wet in San Jose and wondering just how out of the ordinary is this weather pattern?

I’ve “only” lived here about 35 years, and that’s just barely over 1/2 of a PDO “cycle”. So is this really “odd”, or is it just 1/2 of “normal”? I started by asking someone who first moved here about 50 years ago. They said it reminded them of what it was like when they first moved here… So, any objective evidence?

Now

First off, here is a chart of the last year leading up to “now”:

San Jose May 2010 2011 Wunder

Original GIF image

There are a couple of things to note about this chart. First off, the black lines are the “normal range”. I was a tiny bit surprised when looking at other years on Wunderground to find that the “normal range” changes over the years. I have no idea how they calculate it, but it is something to watch for when comparing old to new charts. Look at the scales to know what “normal” is…

Next up, notice how all summer long the average temperature does not go near the “upper normal” line? It just hangs about 65 F. (That’s the “average mean” I think… I know that daily MAX has been higher).

Winters and Dec / early Jan in particular, tend to about the 45 F line, while in late Jan / February there is a brief warm “bump” to the upper “normal” line. Then in Mar Apr and May we get oh so brief “bumps” up to the upper “normal” line but they then slump back down to about the same as December, well below the 60 F line.

So, is that “normal”?

Now look at the bottom box. Wind direction. Looks like it’s scattered all over. Above it, wind speed, has nice dots for “gusts” showing up regularly in the 25 MPH / 35 KPH range. Very gusty. (I’ve mentioned before how the wind has seemed more “bursty” or “gusty” to me… any truth to that, or are these gusts “normal”?) Typical wind running between 6 and 10 mph or 10 – 18 kph.

Lets compare this with 1995 – 1996 era data, back when we had “Global Warming” and were warm and comfortable, shall we?

San Jose May 1995 1996 Wunder

Original GIF image

Gee… all of 4 wind gust dots. Wind is very consistent at a north northwest direction most of the year at “5 or less” MPH (nearly no winds) only getting that “scatter plot” look to the wind direction during the middle of winter.

Summer temps hanging closer to that “normal high” line in the 65 F to 75 F range (with spikes to 80 F) and winter tracking right along the “normal high” line at about 60 F. A brief “dip” at the end of February, but generally nice warm springs.

I’ve downloaded (and saved) every Wunderground chart for every year they have (from 1948 forward) both on a “May to May” and calendar year basis. This general pattern holds. So yes, this example is a slight cherry pick in that I did choose (semi-randomly) one that illustrated the effect reasonably well. But there are a LOAD more with the same general evidence and conclusion. Some examples (that were randomly chosen by “click”):

San Jose May 1991 1992 Wunder

San Jose May 1993 1994 Wunder

Not exactly as clean an example, but similar. How about years after the Great Climate Shift of 1998?

Notice how much larger the range is now on the scale for “gusts”. We had some 100 mph+ gusts in some of those years.

San Jose May 2004 2005 Wunder

San Jose May 2005 2006 Wunder

Before the Shift of 1975

So, if we look back before the “cold shift” of about 1975, what pattern can we find? Well, the very old data in the ’40, ’50s and ’60s has no wind recorded at Wunderground. For them we can only compare temperatures. But in the ’70s they did save the wind data. Lets look at a couple.

One of the very first charts with “gusts” on it (and I’m not sure how good they were about recording all the gusts then) does have rather nice strong gusts:

San Jose May 1973 1974 Wunder

Wind direction a bit “scattered” then too.

It looks to me like the “normal” lines run a bit hotter, or perhaps just wider ranging, but otherwise temperatures are about like they are “now”.

Even in 1975-76 we’ve still got the “scattered” winds effect.

San Jose May 1975 1976 Wunder

but by a decade later it’s resolved nicely:

San Jose May 1984 1985 Wunder

Wayback

If we look further back in time, we have no wind data. The temperature curves are interesting, though. For these graphs I’m using the Jan-Dec time period. Yes, you will need to ‘visually shift’ them to match the ones up above. (Wunderground choked on some of the ‘cross year’ graphs – I think it was when the “normals” changed and / or when they had data dropouts, such as 1963 when JFK was shot and the don’t have several months of temperature data.)

San Jose Jan 1949 Dec 1949

San Jose Jan 1965 Dec 1965

For these two, I think you can still see pretty clearly that as we fell off the peak of heat of the mid ’30s the temperatures then were not that much different from what they are now. About 7 C mid winter (though a bit more cold in ’65) and summers about 65 to 70 F. That “summer flat” in ’49 is very oddly similar to the one we had this last year…

In Conclusion

I don’t see “climate change” in these detailed graphs. I do see a normal long cycle pattern playing out, and I see hints of some UHI as the airport grew to acres of tarmac surrounded by miles of cars and winter heaters.

It looks, to me, like there are clear “hot PDO” vs “cold PDO” indicia; where the hot phase has soft warm summer breezes, while the cold phase as gusty stormy events all year long. I suspect similar graphs could be made for most of the coastal cities of North America ( and likely something similar for other geographies as well, such as Chile or Peru). For Europe, the AMO shift often happens about 10 years after the PDO shift, so a ten year offset to the 1975 date would likely be more interesting.

A random spot check of 2 graphs from Portland Oregon would seem to confirm it:

Portland Jan Dec 1994

Notice that it is much cooler, even using a lower scale, in the “now” graph of 2010 compared to the “then” graph of 1994. There has clearly been a cold shift. At the right hand side, it has Dec lows near the -1 C in 2010, but about the 4 C line in 1994. The high peaks in summer hit the 24 C line now, it was 27 C in 1994. The gustiness has changed to more gusty too, though the wind direction effect is somewhat different. Less clear. Summers more stable in the “hot phase” while winters look a bit more stable, and from a different direction, in the current cold phase.

Portland Jan Dec 2010

So I would count that as a “Giant Dig Here!”.

There is clearly something dramatic that happens with winds (that are known to affect the degree to which the Airport Heat Island effect is registered) and a significant temperature shift that happens with the PDO. As of about 1998, it has shifted to the decidedly cool side. This is not just “recent weather” going away next year; this is a 30 year shift to the cold side.

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