Thunder in Winter
Snow in 7 Days

Last week we looked at the science behind a red sky. This week we won't be looking, rather, we'll be listening for the sound of thunder in the sky. As the saying alleges, roughly 7 days after a thunderstorm, snow is said to start falling. I've heard it a couple times this winter and it's a 'lore that has been prevalent here in the east. That being said, let's do some investigating and see how the folklore holds up to actual observations.

The Data
The National Weather Service has a sensor that will indicate when a thunderstorm is in the vicinity. As mentioned in the video, when thunder is heard by the sensor the number 3 is placed in the day's weather report. So to test this folklore it would make sense to find the days where thunder was reported and see what weather was observed 7 days after that fact. Pretty simple, but very revealing. How do you think the folklore held up?

Results
Like most folklores, if you stick to the exact wording, it will prove to be rather, well, unscientific. In fact, this folklore failed completely by not recording one snowfall event seven days after a thunderstorm. The data set started in February of 2007 and included the months of December, January and February. Going by the numbers, the folklore never accurately predicted snowfall.
But! like any good folklore, we can't take it too literally. Rather we have to let it breathe a little and then look for some forecasting qualities. For example, if we expand the number of days to, say, 8 or 9 and change the word "snow" to "cold temperatures" then, the folklore actually holds up to the percentages. Of the events found, 50% of the time cold air (highs in the 30s) came through roughly 7-10 days after a thunder report.

I guess a more appropriate saying would be:
"Thunder in Winter, Cold Temperatures in About a Week"
but that just doesn't have the same feel as the original folklore.

While it may not predict a snowstorm, it does a decent job forecasting at the very least cold air. Check out the video to see what I mean.

Remeber:
A new set of 'lores will be up for voting on Sunday morning. Join us at 7:30am on WITN to cast your vote for the next World of Weather folklore topic.