predicting the weather..

[thatguy]

I have a possibly stupid question. I want some help understanding weather predictions.

lets say we have a 30% chance of rain/snow - Does that mean it will rain/snow for 30% of the day or just we about 1/3 chance of rain/snow?

I am guessing the percentage has nothing to do with the length of the time it rains or snow.. Just the chance that it will rain/snow..

thanks

Brian

 

[Bird]

Brian, I don't really know for sure myself, but I used to think 50% chance of rain meant it was even odds that it would or would not. However, I have been told that it means 50% of the forecast area will receive rain.

And right now, the forecast is for a 10% chance we'll get a light snow tomorrow.

 

[CharlieTR]

I heard a weather man mention this many years ago and I was sort of suprised to hear what "chance of ..." actually means.

Example: 65% chance of rain means in the last recorded 100 days with the exact weather conditions it rained 65 days of those 100 days.

 

[avorancher]

I thought your question was interesting so I did a lot of internet searching. Turns out that there are many different opinions on this. The link below seems to be the one supported most by "weather-related" postings and not just people in discussion groups.

Listener Question-Forecasting Percentage

I think the "% chance" terminology they use today started when computer-forecasting became popular. I also thought it was weird when I first heard it being used. To me, it seems like 100% chance means that there IS a chance.

 

[Amontilado]

Folks,

The way the NWS defines a "chance of precipitation" is the possibility of a measurable amount of precipitation being recorded, whether it is rain (0.01"+), snow(0.1"+), ice(0.1"+), etc. A lot of the guidance we use is statistical in nature, in that, when a computer model had these conditions over an area, this is the average temperature, high or low temperature, rain coverage, etc that was recorded at a measuring point (usually an airport) that records the weather (these conditions gave a measurable amount of precip xx% of the time, on average).

Steve

 

[johnk]

Thats the only Occupation that you can use all the subjunctives of possible, partly, Potential, mostly, could, and have all the bases covered. If an eartquake occured they would say the potential was there and it could possibly happen again tomorrow. If it doesn't everyones relieved. If it does the weatherman is a hero..........How much they Make???? $$$$$$$$. If I used all the phrases they use in my occupation I'd be fired. Whaen the boss asks if I did it a certain way and I said possibly, could have etc I'd be looking for another job...

 

[Bird]

Thats the only Occupation that you can use all the subjunctives of possible, partly, Potential, mostly, could, and have all the bases covered.

Well, you could be a doctor or lawyer, charge big fees, give absolutely no guarantees, be wrong at least as often as the weatherman, and make even more money.

 

[Amontilado]

Our phaseology is dictated by a stack of binders one to two feet thick. Since I'm so used to using specific wording, it irritates the heck out of me when I hear some of the "weather talent" mix their phrases, usually with the effect of trying to cover all the bases, "in case". JMHO.

Steve

 

[mikim]

yeah Steve --- but we won't get into the old met vs. et "who has to be right what % of the time" debate .....I'll let Brian handle that for me. (I'm assuming here that you're at HUN) ....

 

[the_sandman_454]

The only real forecast that can be relied upon is as follows: Statistically there's roughly a 50% chance the weatherman will be right.

If I was a weatherman I'd simply suffice it to say "There is a 100% chance of between 0 and 10 feet of precipitation today". I'd be a hero, being right 99% of the time...