Is it most likely to rain with a 30% chance?

Question

I'm gonna be going to an amusement park this saturday and the weather forcast says that there is a 30% chance of thunder storms? Will this ruin my weekend?

Answer 1

This is a common misconception to the average American and something that everyone needs to be educated on since weather affects EVERYONE. This 30% chance of thunderstorms is for the forecast area. For example...I'm from Louisville, KY and a National Weather Service office is located there. The forecast area or area of responsibility (AOR) covers north central KY and south central Indiana. If you have an atlas handy, basically draw a 100 mile ring from Louisville and that's their AOR. Lots of counties are included. This 30% means that the forecaster anticipates that 30% of the AOR to receive thunderstorms. Even though this equates to a 30% for the entire AOR, the risk for thunderstorms is averaged. Thunderstorms may be more likely in certain areas of your area...i.e a cold front is slowly pushing west to east. Those in western counties could easily get the thunderstorms and your area be completely dry. The forecaster can then go back and easily verify his/her forecast as a good forecast as 30% of the area actually did receive these thunderstorms. Typically during the warm months in the southeast U.S. though, a threat for afternoon/evening thunderstorms is very common and pinpointing exact locations of thunderstorms is very difficult. The reason for these thunderstorms is simply the Bermuda High. The Bermuda High fuels thunderstorm development in the southeast as the western half of the high is unstable. Rotation around a high is clockwise, so Atlantic and Gulf moisture is advected into the region. The polar front jet stream is well off to the north during this time (in Canada), and winds throughout the troposphere are not nearly as strong as the winter. Add all those together (instability, high moisture content, weak winds throughout the vertical column), and daytime heating as slow moving thunderstorms are a result. Like I mentioned before, with these thunderstorms being so hit and miss (and now slow movers, typically), 30% is commonplace. No one praises the weatherman for being right, it's when they are wrong that the weatherman gets blamed. Being a weatherman myself, when I get approached by these people, I encourage them to get their degree in Geosciences, etc. and do it yourself since they don't like it so much. Truth is, meteorology is NOT an exact science. It's mainly based on probabilities of certain phenomena to occur/not occur. Most of the time the are actually correct, uncommon to popular belief.

Answer 2

Thunderstorms will most likely occur in the forecast area. The storms are restricted by the size of the cloud producing them. You could have a storm a kilometre away that doesn't affect you.

A 30% chance means that three times out of ten, thunderstorms will occur. I would take a fold-up umbrella with me just in case but go to the park. If a storm develops and gets close, go to an indoor area until it passes. It is unlikely to last more than 30 minutes.

Answer 3

When we say 30% chance of rain, that usually means that there will definitely be a threat of rain and it will either hit your area, pass to one side, or pass to the other. However, any rain will be relatively short, it won't be a wash out. Go to your thing, enjoy the nice autumn outdoors, but pack an umbrella or rain jacket just in case.

Answer 4

if it says that there is a thirty percent chance of rin, then that means that if you replayed the weekend 100 times, it would rain thirty of those times. the chances of rain are fairly low, and (asuming that there is a 70 percent chance of sun) not likely to ruin your weekend. a good way to think of this is if you flip a coin, there is a beter chance of it landing on heads than there is of it raining.

Answer 5

30% ruin, 70% not, take umbrellas in case. Sounds like short, spotty showers.

Answer 6

Id say there is a 30% chance..

ha.. but weathermen dont know what they are talking about.. ever