November 22: Warmer Today, But Does A Cool November Lead To A Cold Winter?

Weather

WEATHER

We’re going to take a nerdy look ahead to winter later in this post, but first let’s get the short-term forecast out of the way. Today will be cloudy but mild, with highs in the low to mid 60s this afternoon.

A few passing showers will be possible — they’ll be few and far between, with the best chance along the Virginia state line.

The clouds will stick around tonight…despite the atmospheric blanket, temperatures will drop to the mid 40s as winds turn to the northeast.

Saturday will a gray, cool, wet day overall. I think we’ll start the day dry, but rain showers will become more likely by midday, with the heaviest rain falling in the evening and overnight. The North American Model’s radar simulation from 7:00am Saturday through 7:00am Sunday shows that the last of the rain will be gone by sunrise.

If you’re heading to the Raleigh Christmas parade tomorrow morning, bring the umbrella and rain jacket — rain chances will increase every hour you’re out there, and it won’t be warm.

Dry weather will prevail for the first few days of Thanksgiving week. We’ll climb back to the upper 50s on Sunday, then reach back into the low 60s Monday and Tuesday.

A cold front on Wednesday won’t have much moisture to work with around here, so I don’t think we’re looking at much of a rain chance for that very busy travel day. Thanksgiving itself looks dry, with near-normal temperatures.

COLD WINTER? SNOWY WINTER?

Wes’ winter preview story aired on CBS 17 last night, but I’m going to take a longer look at something very specific: whether there’s any connection between this month’s cooler-than-average temperatures and what we can expect this winter. We’re going to get nerdy here, so I’ll use some Ron Swanson GIFs to keep your attention.

Too late, here we go! First, let’s establish that this month HAS been substantially cooler than normal. If today was the last day of November, this would go into the books as the 9th-coldest November on record in the Triangle! But of course, we’ve got another week to go…near-normal temperatures in the forecast through the end of the month will affect that ranking. We’ll still end up in the top 25 for the coldest Novembers on record — that’s significant, considering that record-keeping goes back to 1887.

So, does a colder-than-normal November increase the odds that we’re going to endure a colder-than-normal winter? It might seem logical, but my experience a meteorologist tells me that short-term weather patterns are rarely reliable indicators of long-term climate trend.

That said, any halfway-decent scientist wants proof. So, I dove into the record books to look for answers. If you want to definitively state that there is a direct correlation between November temperatures and following-winter temperatures, you have to look at all the data, and plot every November temperature against every winter temperature.  If there’s a direct relationship, the chart would look like this…

Here’s what the chart really looks like for November vs. Winter temperatures.

Quickly glance at that, and you probably notice the line through the dots — that’s the “best-fit” line that attempts to summarize all the data points in a straight line. “AHA!” you say, “that line goes UP! Therefore, a cooler November equals a colder winter, and a hotter November equals a warmer winter!”

There’s a way to measure the accuracy of that “best-fit” line…it’s called the “Coefficient of Determination,” and it’s abbreviated as R-squared. (Why is it R-squared instead of CD? Why isn’t it called something simpler? These are questions I asked my statistics professor in graduate school, and the answers were…unenlightening.)

Anyway…that “Coefficient of Determination” tells us whether the best-fit line does a good job of summarizing the data, or whether it’s just the software doing it’s best to pound a square peg into a round hole. An R-squared value of exactly 1 means that it’s a perfect fit, while values closer to zero mean that there’s really no relationship between the two things you’re trying to compare.

For November temperatures vs. Winter temperatures, the R-squared value is 0.09. That’s low, indicating an at-best slight correlation. Basically, it tells us that with over 130 years of data, there is very little predictive relationship between temperatures in November and temperatures the following winter. I wouldn’t be comfortable basing a cold winter forecast on such flimsy correlation.

Just one more question…what about snow? Again, it seems logical that an early arrival of colder air would boost our snow chances later on. Here’s the chart of November temperatures compared to snowfall the following winter.

That’s even more of a mess! The R-squared value is really really low, barely above zero. So I can confidently say, there is NO relationship between temperatures in November and snowfall the subsequent winter.

Bottom line: whatever the weather is going to do this winter, this month’s chilly temperatures don’t have anything to do with it.

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