What’s in a number? Well, actually, a lot can be stated or summarized in a single number! Sometimes, way too much can be stated in a single summary so that you lose the details of how you arrived at that point. That’s how climatology works. Too many times, we say “the average high” or the “average low” for a particular day is this or that. For example, today’s averages at the Birmingham International Airport are 56 for a high temperature, 35 for a low temperature, and according to the books, we should see, on average 0.14” today. The actual weather that we experience will most likely be significantly different than the averages.
Sometimes we call those average highs, lows, and rainfall amounts the climatology data for a certain city on a certain day. It’s useful because it gives us a meter stick to measure extremes by, but that’s about it. Climate data is measured over 30 years, so if you took every single high temperature and low temperature for today and averaged them together, December 14, you would come up with 56 and 35. All rainfall measured is averaged too, and it comes to 0.14.” Yesterday’s weather compared to that meter stick was “below normal” with a high of 52, low of 28, and no rain at all. It was close enough to the average, though, to say it was “a typical December day,” and it reinforces the flawed idea that all forecasts should trend toward climatology.
As meteorologists, sometimes we (or at least I) have a tendency to be conservative with a forecast because I focus too much on the meter stick and not on the entire picture. That’s a dangerous place to live because there are going to be extreme events that get “evened out” when everything gets averaged up. That record high of 77 set back in 1971 and the record low of 14 in 1917 don’t really stand out in the 56 and 35, but they are there! The big Blizzard of ’93 doesn’t show up well in the averages for mid-March, but it is in there. Hurricane Ivan’s rain doesn’t show up well in the September rain averages either! The point is simply this, just because the books say that Birmingham’s average high for today is 56 does not mean we will always be close to it.
If we always stay with climatology and averages, then there is no way we will ever get an idea that something extreme could happen. The atmosphere is a complex ocean of air with many currents moving air around in all directions. Forecast models do an o.k. job of guiding us toward a forecast down the road, but those models are very near-sighted. After 72 hours, they really start moving toward climatology and away from extreme ideas. You can bet your bottom dollar that no forecast model seven days in advance forecasted a low of 2 above zero in Birmingham on the morning of March 14, 1993 after 13 inches of snow had fallen in the two days prior. Climate data is great. We need a good climatology of an area, but to get the full picture of how the weather really is for a region, state, or city, sometimes you have to go beyond just a simple number.
Sometimes we call those average highs, lows, and rainfall amounts the climatology data for a certain city on a certain day. It’s useful because it gives us a meter stick to measure extremes by, but that’s about it. Climate data is measured over 30 years, so if you took every single high temperature and low temperature for today and averaged them together, December 14, you would come up with 56 and 35. All rainfall measured is averaged too, and it comes to 0.14.” Yesterday’s weather compared to that meter stick was “below normal” with a high of 52, low of 28, and no rain at all. It was close enough to the average, though, to say it was “a typical December day,” and it reinforces the flawed idea that all forecasts should trend toward climatology.
As meteorologists, sometimes we (or at least I) have a tendency to be conservative with a forecast because I focus too much on the meter stick and not on the entire picture. That’s a dangerous place to live because there are going to be extreme events that get “evened out” when everything gets averaged up. That record high of 77 set back in 1971 and the record low of 14 in 1917 don’t really stand out in the 56 and 35, but they are there! The big Blizzard of ’93 doesn’t show up well in the averages for mid-March, but it is in there. Hurricane Ivan’s rain doesn’t show up well in the September rain averages either! The point is simply this, just because the books say that Birmingham’s average high for today is 56 does not mean we will always be close to it.
If we always stay with climatology and averages, then there is no way we will ever get an idea that something extreme could happen. The atmosphere is a complex ocean of air with many currents moving air around in all directions. Forecast models do an o.k. job of guiding us toward a forecast down the road, but those models are very near-sighted. After 72 hours, they really start moving toward climatology and away from extreme ideas. You can bet your bottom dollar that no forecast model seven days in advance forecasted a low of 2 above zero in Birmingham on the morning of March 14, 1993 after 13 inches of snow had fallen in the two days prior. Climate data is great. We need a good climatology of an area, but to get the full picture of how the weather really is for a region, state, or city, sometimes you have to go beyond just a simple number.
but all these others are Greek. how about where to begin to learn what the letters for the models stand for. Any suggestions for resources, Web or paper.
on December 14, 2005, 8:37 am
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