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Winter Outlook Part 1

The first part of my winter outlook will start off with some definitions and clarifications. I want to emphasize that both climatology and long-range forecasts are extremely complex topics. In fact, even the most seasoned meteorologist will make a mistake by saying that day-to-day weather is "normal" or "seasonal". Here is some data from this month to show you what I'm talking about.

These are the measured high temperatures in San Diego, CA and Richmond, VA for the past ten days:


San Diego
Oct 17...86
Oct 18...88
Oct 19...85
Oct 20...80
Oct 21...81
Oct 22...85
Oct 23...90
Oct 24...79
Oct 25...62
Oct 26...66


Richmond
Oct 17...82
Oct 18...81
Oct 19...70
Oct 20...63
Oct 21...66
Oct 22...64
Oct 23...66
Oct 24...70
Oct 25...70
Oct 26...77

The 30-year average high for San Diego in late October is 72 while in Richmond it is 68. Notice that none of the measured high temperatures match the average high (each day is above or below the average).

So if you are a meteorologist who lived in San Diego, why would you describe Oct 24 as "unseasonably warm" if every October you see highs reaching the upper 70s? Similarly, if you lived in Richmond, why would you describe October 26 as "unusually warm" if every autumn temps rise to this level? I had a professor who said it best: "The most normal thing about weather is that it is abnormal". This is a great way to describe day-to-day weather. A 30-year average for a specific date is worthless (like when you hear a meteorologist say "Today's normal high is...)

You should only use the average over several days or weeks to describe something "unseasonable". This will be key when I talk about long range outlooks and how they compare to the average.

Ok, I'm now done with my weather vs. climate rant :)

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