Well, how does that explain such a warm and mild winter here in the Pacific Northwest?

My question pertains to measurement and utilization of coldness data. How does one take measurements that track coldness over an entire country? Are there, for instance, 1000 thermometers mathematically scattered over each state in the USA, and the mean temperature of each device read, say, 10 times a day? Every day for a year. Then, is somehow the mean temperature for the entire USA calculated by compiling data?

Just having one thermometer per state, or only measuring North Dakota for instance, which everyone knows is frigid in winter, would not accomodate geographic variations. And, of course, time of the day is important.

So, when they are calculating the coldness of the year, what are they really measuring?

Oh gawd. Guess it was to much to hope for an easy question, you know, "Is it the weekend yet?"

Lets see if I can give useful answers.

Earth's climate is a world wide thing. Within that are many, many climate sections. They're influenced by things like mountains, oceans, large bodies of water (Think Great Lakes), and a lot of other things. You can carry that all the way down to the microclimates in your yard. Plants that may normally be more southern by a zone or even 2 than your place might survive if they're planted close to a west facing wall because that wall creates a microclimate that's warmer than the rest of the yard.

Why the Pac NW was warmer and drier than usual this year could take me a month to dig out.

Being global, the number of measuring stations in the US should be a relatively small part of the answer.

What I do know about US stations is this:

They tend to be located near cities - and the heat islands cities create.

There is a web site that has many, many examples of these stations being in places that mean the readings they give are false. For example, one unit is (May have been corrected since last I looked) in the exhaust from an air conditioner. You know, all that heat sucked out of the house is blowing on the thermometer. http://surfacestations.org/

There are a fair number of sites in the US. You can dig out the complete list of the ones the National Climate Prediction Center uses here: http://www.cpc.noaa.gov/products/global_monitoring/temperature/global_temp_accum.shtml

Ground stations are not the only way temp is measured.

Satellites cover much of earth twice daily. Those readings do not agree with the ground temps. This is a pretty good not too technical explanation of the way it's done and the results. About 10 years old but still pretty accurate: http://science.nasa.gov/newhome/headlines/essd06oct97_1.htm

Did I at least get a good start on answering the questions?

COOL topic bound to get HOT comments. I did some research so thanks for presenting it here. I have a few good years left in me supposedly, so I'll just observe what remaining years I have left in this century to see what develops.

Arent global warming and global cooling, 'two sides of the same coin'?

That's as good a way to look at it as any other.

Earth cycles, warm cool, hot, cold. And there are cycles within cycles. For example during this cycle from an ice age to the warm period we've had a mini cycle with The Little Ice Age and the Medieval Climate Optimum (MCO).

It's worth remembering the MCO was warmer than today. And it coincides with a period of great growth for humanity.

I know this will stir up some ... debate... shall we say, but here goes.

*

The winter weather we have experienced this year has been related to, but not strictly controlled by, two major factors. The first is the La Nina cycle in the Pacific Ocean. The second is the early fall snow coverage in Siberia.

*

THE LA NINA

*

One theory is that this La Nina is simply a snap back from the previous longer term El Nino cycle.

The El Nino is a result of build up of warm water in the western Pacific Ocean. The prevailing east to west winds blow the warmer surface water from east to west. The water actually builds up to the point where the sea level in the western Pacific is higher than the sea level in the eastern Pacific.

This can only go on for so long until the wasrm water surges back toward South America. That is when we get an El Nino. The warm water rushes east, pushing the cold water down and west. The warm surface water has huge effects on the weather patterns in North America. Some good, some bad. We get fewer hurricanes, droughts in the southwest and southeast, and really hot weather up here in Wisconsin.

When the El Nino overcorrects, we get a surge of surface water back to the west causing cold water to come up to the surface off of South America. This strongly effects weather patterns in North America just like the El Nino but opposite. The strength and number of hurricanes predicted for this year is still under debate and will depend on the longevity of the La Nina. The cold winter weather over the northern midwest was predicted back in October by NOAA when the La Nina started. They predicted an average increase in heating costs of 10% completely separate from fuel unit prices. I think they were sandbagging myself.

*

SIBERIAN SNOW COVER

*

The amount of snow cover in Siberia early in the winter effects the amount of sunlight absorbed/reflected in this area of the world. High snow coverage reflects more sunlight making much of the artic colder. This in turn strengthens the high pressure phase of the Artic Oscillation. This in turn pushes the northern jet stream farther to the south. This gives us weather like what we are experiencing this weekend. Significant cold and snow as far south as Arkansas as the northern jet stream dives to the south.

Fortunately for the Northwest, you get the nice northern hump in the jet stream that brings that nice warm south wind.

*

As climate change continues to develop, we will see more frequent and stronger swings in the El Nino, La Nina cycle. What it will do to the Siberian Snow Cover variable, we will have to wait to see.

For those of us with teenage children wondering what line of work to go into, I would suggest they learn to design larger and better water reservoirs as we will see larger swings between droughts and floods.