Does it really snow 10 days after we hear thunder in the winter?

RALEIGH (WTVD) -- Any time a storm brings thunder to the South, the rumors will start: "Get your milk and bread. Snow is on the way."

On Twitter, Facebook, and through email, people are already asking the ABC11 First Alert Weather Team, "I heard thunder. Does that mean it's going to snow 10 days from now?"

This is a question I've been asked every year since I've been here, and I wondered if there was any truth to this weather lore or is just hokum. So, I decided to do some research.

I looked the hourly weather records for the past 50 years at RDU.

I know, you might be saying, "Why RDU? That's not in my neighborhood!"

Well, RDU has one of the most complete sets of weather records in the viewing area, and I knew I would find the data there.

Next, I logged on to the NCDC to find the data I needed.

Finally, they sent me the data.

By the way, to get the hourly data, and accompanying hourly remarks, you need to download a PDF file with 33,388 pages. Whew, that's a big PDF!

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Then the crack ABC11 Weather Research team (my wife & I) combed through the data.
First, we found every day snow was reported at RDU, with at least a trace or more.

The approximate total was 382 days.

I say approximate because my eyes were starting to cross looking at that PDF file.

Out of those 382 days, just under half of them (176) had some type of precipitation fall 10 days before.

Then I went back to the weather observations and looked to see if thunderstorms were reported on those days.

Only 11 times did it thunder 10 days before the snowflakes flew.
To put that in a percentage, 97.1 percent of the time when we get snow, it did NOT thunder 10 days before.

As you look at that number, some of you might be thinking 2.9 percent of the time it DOES snow 10 days later! And you would be right.

As Lloyd said in 'Dumb, & Dumber', "So you're telling me there's a chance!"

Then I decided to look at how many days it thundered in the winter,and go forward 10 days, and see if it snowed.

Well, here is what I found...

I logged on to the NC State Climatologist's office and looked at the last 50 years of weather reports from RDU, 1966-2016. The total number of weather reports totaled 411,596! It took me a few days to go through that, even with a fast computer.

I looked for every hourly report that thunder was noted in at RDU in the months of December, January, and February (those three are winter months in Meteorology). I also added in March because winter doesn't end on the calendar until then, and we do see snow.

There were 129 times it thundered in those months. 5 times it snowed 10 days later. That means it snowed 3.9 percent of the time, just 1 percent more than my original findings. But a funny thing happened on the way to those numbers.

I was discussing this with one of behind the scenes folks, AnnMarie, and she said, "I thought it was supposed to snow sometime in the next 10 days, not exactly 10 days out."

Well, that's a horse of a different color. So I went back to the numbers (more research can be done).
Here's what they showed.

Out of the 129 times it thundered in those months, it snowed 25 times within 10 days. That upped the percentage to 19.4 percent of the time. I was a bit surprised at that many, but it does make sense.

For thunder to happen you have to have all kinds of active weather in the atmosphere, and with precipitation averaging every 3 days in our area during the winter, thatt seems about right.

So, the next time it thunders in the winter in our area, there's almost a 20 percent chance we will have snow in the next 10 days. I know more research can still be done: looking at different stations, looking to see if freezing rain or sleet also falls, etc., but I'm done for now.

It's funny. Those old weather sayings have had to have some truth in them, or they wouldn't have stuck around so long.
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