Over the nearly 30 years that I have been working in television giving viewers their daily forecast, a common question that I have received has been ” What does it mean when you say there is a 30% chance of showers on your 7-day?” This question is a legitimate one, considering all weather forecasters tend to be very numbers based. So, if there’s a 30% chance of rain, what does that mean? Basically the odds of you seeing rain is 30%, but a 70% chance you won’t see a drop of rain. Another way to understand it is if someone were to say, “my schedule is busy, so there’s only about a 30% chance I might make it out to dinner with you later tonight.” In addition, the chance of precipitation does not indicate the intensity or for how long the rain might fall. There could be a 20% chance of a pop-up thunderstorm, but yet that thunderstorm could still yield heavy rainfall, and an 80% chance of rain does not mean it will rain 80% of the day. The chance of rain in the summer is low many days, since thunderstorms can be few and far between, and its days like that, we say isolated to scattered showers.

The sun sets behind a windmill, Saturday, Sept. 2, 2006, near Abbott, Texas. North Texas reached the low 90’s and was mostly cloudy with some showers and thunderstorms. (AP Photo/Matt Slocum)

The other one that gets folks, is when we, as on-air talent, verbally state that it will be “partly cloudy”, “variably cloudy” and the like. I always like to say to folks, that imagine the sky is a piece of pie and you want to divide up the pie into different slices. In order to classify the sky as overcast, 100 percent of the sky needs to be covered by clouds. It does not matter which types of clouds are visible, just the amount of the atmosphere they cover. Meteorologists use a scale to define cloud cover, and as I just alluded to, is represented by a pie chart divided into eight slices, with each slice representing a percentage. For an overcast sky, the pie is completely filled and it is cloudy. A “mostly cloudy sky” is classified as 70 to 80 percent cloud cover with a 20 to 30 percent of sunshine. On mostly cloudy days, you will be able to see some sunshine in between the clouds and can also be referred to as “partly sunny”. Bottom-line, “partly sunny” seems a bit less gloomy than “mostly cloudy,” psychologically, even if you think about it from an English perspective where they should technically mean the same thing. If the pizza is “mostly” gone, there is still some pizza “partly” leftover, right? Now that I have hopefully successfully explained some of the weather questions that you have had in the past, here is the official breakdown by the National Weather Service cloud cover definitions, based on our “pie chart”. The sky is considered “sunny” with 1/8 or less of cloud coverage, “mostly sunny” when 1/8 to 3/8 of the sky is obscured by clouds, “partly cloudy/partly sunny” when 3/8 to 5/8 of the sky is covered, “mostly cloudy” when 5/8 to 7/8 of the sky is cloud coverage and “overcast” 7/8 to 8/8.

Photo Credit: NWS

The challenges of weather forecasting are well known, as weather systems can range from small, short lived storms that last a couple hours to large scale rain and snow storms that last for days. Once a meteorologist has created a forecast that they are happy with, their next role is to deliver that forecast to folks that can understand and appropriately respond to. I have given you a bit of insight into how weathercasters approach putting together a local forecast based on the data given, and while our job may come across as easy, it is certainly the furthest from the truth, as we try to predict what has yet to happen. So the next time time you hear your favorite forecaster say there is a 30% chance of rain, its the furthest thing from a washout and you will be able to get in the that walk, jog or run. Well that does it for this weeks podcast, in the mean time, God bless, stay safe, and we’ll see you next week.