Weather forecasters can only physically measure conditions for the current day. How can today's conditions be used to predict tomorrows chances of precipitation? The forecasters will be able to physically count the total number of days in the past that had the same or very similar conditions as today. Then they would look at what weather actually occurred for the following day (in the past). If they chose to look at the last 100 days that had the same conditions as today, then they could determine very easily whether or not it rained the next day. They now have the required data to calculate the chances of precipitation. So if the rain occurred on 60 of those days, then there will be a 60% chance of rain tomorrow.
Bill Berry - 14 years ago
The correct answer is a combination of two factors - confidence and area; confidence being what the forecasters believe and area of concern. As a forecaster I never by definition forecasted 100 percent; mostly 80 and 90 percent and of course summer anything from 40 percent up was a sure thing!
Bill Berry - 14 years ago
Courtesy of the NWS - Explanation of Probability of Precipitation
Forecasts issued by the National Weather Service routinely include a "PoP" (probability of precipitation) statement, which is often expressed as the "chance of rain" or "chance of precipitation".
EXAMPLE
ZONE FORECASTS FOR NORTH AND CENTRAL GEORGIA
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
119 PM EDT THU MAY 8 2008
GAZ021-022-032034-044046-055-057-090815-
CHEROKEE-CLAYTON-COBB-DEKALB-FORSYTH-GWINNETT-HENRY-NORTH FULTON-
ROCKDALE-SOUTH FULTON-
INCLUDING THE CITIES OF...ATLANTA...CONYERS...DECATUR...
EAST POINT...LAWRENCEVILLE...MARIETTA
119 PM EDT THU MAY x 2008
.THIS AFTERNOON...MOSTLY CLOUDY WITH A 40 PERCENT CHANCE OF
SHOWERS AND THUNDERSTORMS. WINDY. HIGHS IN THE LOWER 80S. NEAR
STEADY TEMPERATURE IN THE LOWER 80S. SOUTH WINDS 15 TO 25 MPH.
.TONIGHT...MOSTLY CLOUDY WITH A CHANCE OF SHOWERS AND
THUNDERSTORMS IN THE EVENING...THEN A SLIGHT CHANCE OF SHOWERS
AND THUNDERSTORMS AFTER MIDNIGHT. LOWS IN THE MID 60S. SOUTHWEST
WINDS 5 TO 15 MPH. CHANCE OF RAIN 40 PERCENT.
What does this "40 percent" mean? ...will it rain 40 percent of of the time? ...will it rain over 40 percent of the area?
The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point you select in the area.
How do forecasters arrive at this value?
Mathematically, PoP is defined as follows:
PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measureable precipitation, if it occurs at all.
So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)
But, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. )
In either event, the correct way to interpret the forecast is: there is a 40 percent chance that rain will occur at any given point in the area.
Sue - 14 years ago
It means that on a day like tomorrow, it has shown to have rained 60% of the time. The first answer is incorrect no matter how many votes there are. That is the rule of probability. Just like the word reasonable. Someone is reasonable if most reasonable people behaved in the same way.
Mark - 14 years ago
I am sticking with my post of "other" because of the math done on this.
In math it would need to be other, but maybe in weather it doesn't.
LeeW7351 - 14 years ago
As several other posters have pointed out, this survey is invalid because it does not include the most logical answer (which is - the probability of any ONE spot getting precip on the given day) in the list of choices.
greg in homewood - 14 years ago
choice 1 is ridiculous. that implies that it WILL rain. that would equal 100%! this is meteorology 101 folks. measure the atmospheric conditions. on 10 days with similar (nearly exact) conditions it will 6 days and not rain on 4. very basic stuff.
Swami - 14 years ago
OK - I'm now going with OTHER. I still say that 60% probability of any 1 point in the forecast area is correct, but the response selection doesn't seem to include ONLY that answer. There is now a 100% probability that I'm going to take a nap and forget I ever got into this.
Jack Riley - 14 years ago
60% of the time when conditions like this were present in a geographical area in the past, it rained. That explains why when there is an 80% chance, sometimes it doesn't rain, and when there is a 20% chance, sometimes it rains. Choice 3 is clearly the closest to that.
Swami - 14 years ago
It's Probability 101: Since a forecast is for a specified geographical area, that forecast applies equally, by definition, to any point within the area for the specified time period. Hence, #1 is correct. Also, this has been a standard "boilerplate" statement professional meteorologists have included for years in most of their on-air presentations. We "elderly" guys likely recognize that more readily than others because we had to figure out what happened to the probability definition whenever it changed over the years.
alabamapamela - 14 years ago
how can the answer be #3?!!!!!????? "60% chance of rain on days like tomorrow" how many days are like tomorrow, and what's that got to do with it anyway!///? none of them are right. It's a numbers game, a forcast of chance and probability.
Krisitn - 14 years ago
I totally agree with Josh!
greg in homewood - 14 years ago
this isn't even a difficult question. choice three weather geeks! to put it simply- a 60% chance means: if you had 10 days with atmospheric conditions just like a chosen day, then it would rain on 6 of them and not rain on 4 of them. hence a 60% chance of rain! aaaahhhahahahhhh!!!! julie is way off!
Jane - 14 years ago
Julie said it best. There is a 60% chance that any given spot within the forecast area will have rain. There is a 40% chance that any given spot in the area will stay dry. I voted other because I don't think any of the choices were a good answer.
Mark K - 14 years ago
Okay, I used math on probability to figure this one out and I believe it means there is a 60% chance that no matter where in the area you are that there is a 60% chance at some point in the day you will get rain and 40% chance you will not so I am staying with OTHER.
Mark K - 14 years ago
I think I should use Mark K for my name since we have another Mark.
I am the one that voted for other and I am the dumb one. lol
Mark - 14 years ago
I think it should mean there is a 60% probability the areas being forecasts with see rain rather than 60% of the area because there is still only a 60% chance of rain in all areas of the forecast. To say 60% of the area gets rain means there is a 100% chance of rain for 60% of the area and we all know there are days with 60% chance of rain when it does not rain anywhere, or there might be only 20% of the area getting rain.
I am the one that voted for other lol
Mark - 14 years ago
Julie said what I said using a lot fewer words!
Mark...a meteorologist who KNOWS the answer... - 14 years ago
The most correct answer of the ones given is the 3rd choice. The actual definition is a 60% chance that it will rain it any given point within the area covered by the forecast. Forecast probabilities are driven both by uncertainty and also areal coverage. A forecaster can be 100% sure it will rain in the forecast area, but if the precipitation will be scattered, he must determine what percentage of the area will see rain...the entire probability is thus derived from areal coverage. In a different situation, the forecaster may know that if it rains, it will rain over the entire area, but there is some chance that the rain will not make it into the area at all. In this case, the entire probability is based on uncertainty. Most of the time however, the forecast probability covers both uncertainty and areal coverage. The first choice in this poll is only correct some of the time...and that is when areal coverage is the only factor, and not uncertainty. The third choice should always be correct if the forecast is accurate...it should rain at any specific point in the forecast area 6 out of every 10 times the forecast has a 60% chance of rain.
Greg - 14 years ago
An interesting explanation on the subject:
http://www.crh.noaa.gov/riw/forecast/forcast_def.php
Josh - 14 years ago
LOL, Man how did I copy the wrong selection, ignore my above post, I meant: if I had to choose I would have chosen: ("It will rain on 60% of the days like tomorrow."). The others are definitely wrong to me.
It will rain tomorrow in 60% of the area. I believe is wrong because usually a forecast is for a city or a section of a state, and if you say 60% area of a city or state section will get rain and the other 40% will not, is way too unsure or impossible to know.
It will rain tomorrow for 60% of the time. I believe this is wrong as well because is for the chance of rain, not the time frame or the amount of time it will rain that day. For example It can be a like a 30% or 40% chance of rain and sprinkle or rain most all of the day. Or it can be 60% and only rain hard for 2 hours.
It will rain on 60% of the days like tomorrow. This would be the best answer, though could be confusing, if all the conditions for rain chance that day are 60% then the other days that do not get rain but have the same conditions would be 40% of the time.
60% of weather forecasters believe it will rain tomorrow. This is obviously wrong, its about the chance of rain and not the weather forecasters. :-)
But I still like my other first post:
I put "other", and typed It would be a likely 60% chance of seeing rain that day, and a 40% of not seeing rain that day. That's how I've always looked at it, and I believe it's right. It's a chance, and the higher the percent the better chance you have of seeing at least some rain during that day. It's like spinning a percent pie wheel (60% rain/ 40% no rain), it's a game of probability.
JULIE - 14 years ago
I always thought a 60% chance of rain meant that there was a 6 in 10 chance of it raining in any one place.
Josh - 14 years ago
Although I picked other and typed the above, if I had to choose I would have chosen: ("60% of weather forecasters believe it will rain tomorrow"). The others are definitely wrong to me.
Josh - 14 years ago
I put "other", and typed It would be a likely 60% chance of seeing rain that day, and a 40% of not seeing rain that day. That's how I've always looked at it, and I believe it's right. It's a chance, and the higher the percent the better chance you have of seeing at least some rain during that day.
Brandon in Atlanta - 14 years ago
I have actually heard it been said two different ways in my classes. In fact, some Meteorologist incorrectly use the percentage forecast so much so that other Meteorologist refuse to even use the precentage tool as a means of explaining the expected rain chances. Some Meterologist just use the scattered/isolated terminology and leave it at that.
I think I have heard it been said more than once though that the answer is actually number 1 (first choice). I can understand the confusion but I still think suggesting a percentage in forecasting precipitation is very important.
Melba - 14 years ago
It's scary to see how people can read all these different scenarios and still can't come up with the correct answer using COMMON SENSE!!! I should have been a meteorologist! The correct answer is option #3!
Weather forecasters can only physically measure conditions for the current day. How can today's conditions be used to predict tomorrows chances of precipitation? The forecasters will be able to physically count the total number of days in the past that had the same or very similar conditions as today. Then they would look at what weather actually occurred for the following day (in the past). If they chose to look at the last 100 days that had the same conditions as today, then they could determine very easily whether or not it rained the next day. They now have the required data to calculate the chances of precipitation. So if the rain occurred on 60 of those days, then there will be a 60% chance of rain tomorrow.
The correct answer is a combination of two factors - confidence and area; confidence being what the forecasters believe and area of concern. As a forecaster I never by definition forecasted 100 percent; mostly 80 and 90 percent and of course summer anything from 40 percent up was a sure thing!
Courtesy of the NWS - Explanation of Probability of Precipitation
Forecasts issued by the National Weather Service routinely include a "PoP" (probability of precipitation) statement, which is often expressed as the "chance of rain" or "chance of precipitation".
EXAMPLE
ZONE FORECASTS FOR NORTH AND CENTRAL GEORGIA
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
119 PM EDT THU MAY 8 2008
GAZ021-022-032034-044046-055-057-090815-
CHEROKEE-CLAYTON-COBB-DEKALB-FORSYTH-GWINNETT-HENRY-NORTH FULTON-
ROCKDALE-SOUTH FULTON-
INCLUDING THE CITIES OF...ATLANTA...CONYERS...DECATUR...
EAST POINT...LAWRENCEVILLE...MARIETTA
119 PM EDT THU MAY x 2008
.THIS AFTERNOON...MOSTLY CLOUDY WITH A 40 PERCENT CHANCE OF
SHOWERS AND THUNDERSTORMS. WINDY. HIGHS IN THE LOWER 80S. NEAR
STEADY TEMPERATURE IN THE LOWER 80S. SOUTH WINDS 15 TO 25 MPH.
.TONIGHT...MOSTLY CLOUDY WITH A CHANCE OF SHOWERS AND
THUNDERSTORMS IN THE EVENING...THEN A SLIGHT CHANCE OF SHOWERS
AND THUNDERSTORMS AFTER MIDNIGHT. LOWS IN THE MID 60S. SOUTHWEST
WINDS 5 TO 15 MPH. CHANCE OF RAIN 40 PERCENT.
What does this "40 percent" mean? ...will it rain 40 percent of of the time? ...will it rain over 40 percent of the area?
The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point you select in the area.
How do forecasters arrive at this value?
Mathematically, PoP is defined as follows:
PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measureable precipitation, if it occurs at all.
So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)
But, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. )
In either event, the correct way to interpret the forecast is: there is a 40 percent chance that rain will occur at any given point in the area.
It means that on a day like tomorrow, it has shown to have rained 60% of the time. The first answer is incorrect no matter how many votes there are. That is the rule of probability. Just like the word reasonable. Someone is reasonable if most reasonable people behaved in the same way.
I am sticking with my post of "other" because of the math done on this.
In math it would need to be other, but maybe in weather it doesn't.
As several other posters have pointed out, this survey is invalid because it does not include the most logical answer (which is - the probability of any ONE spot getting precip on the given day) in the list of choices.
choice 1 is ridiculous. that implies that it WILL rain. that would equal 100%! this is meteorology 101 folks. measure the atmospheric conditions. on 10 days with similar (nearly exact) conditions it will 6 days and not rain on 4. very basic stuff.
OK - I'm now going with OTHER. I still say that 60% probability of any 1 point in the forecast area is correct, but the response selection doesn't seem to include ONLY that answer. There is now a 100% probability that I'm going to take a nap and forget I ever got into this.
60% of the time when conditions like this were present in a geographical area in the past, it rained. That explains why when there is an 80% chance, sometimes it doesn't rain, and when there is a 20% chance, sometimes it rains. Choice 3 is clearly the closest to that.
It's Probability 101: Since a forecast is for a specified geographical area, that forecast applies equally, by definition, to any point within the area for the specified time period. Hence, #1 is correct. Also, this has been a standard "boilerplate" statement professional meteorologists have included for years in most of their on-air presentations. We "elderly" guys likely recognize that more readily than others because we had to figure out what happened to the probability definition whenever it changed over the years.
how can the answer be #3?!!!!!????? "60% chance of rain on days like tomorrow" how many days are like tomorrow, and what's that got to do with it anyway!///? none of them are right. It's a numbers game, a forcast of chance and probability.
I totally agree with Josh!
this isn't even a difficult question. choice three weather geeks! to put it simply- a 60% chance means: if you had 10 days with atmospheric conditions just like a chosen day, then it would rain on 6 of them and not rain on 4 of them. hence a 60% chance of rain! aaaahhhahahahhhh!!!! julie is way off!
Julie said it best. There is a 60% chance that any given spot within the forecast area will have rain. There is a 40% chance that any given spot in the area will stay dry. I voted other because I don't think any of the choices were a good answer.
Okay, I used math on probability to figure this one out and I believe it means there is a 60% chance that no matter where in the area you are that there is a 60% chance at some point in the day you will get rain and 40% chance you will not so I am staying with OTHER.
I think I should use Mark K for my name since we have another Mark.
I am the one that voted for other and I am the dumb one. lol
I think it should mean there is a 60% probability the areas being forecasts with see rain rather than 60% of the area because there is still only a 60% chance of rain in all areas of the forecast. To say 60% of the area gets rain means there is a 100% chance of rain for 60% of the area and we all know there are days with 60% chance of rain when it does not rain anywhere, or there might be only 20% of the area getting rain.
I am the one that voted for other lol
Julie said what I said using a lot fewer words!
The most correct answer of the ones given is the 3rd choice. The actual definition is a 60% chance that it will rain it any given point within the area covered by the forecast. Forecast probabilities are driven both by uncertainty and also areal coverage. A forecaster can be 100% sure it will rain in the forecast area, but if the precipitation will be scattered, he must determine what percentage of the area will see rain...the entire probability is thus derived from areal coverage. In a different situation, the forecaster may know that if it rains, it will rain over the entire area, but there is some chance that the rain will not make it into the area at all. In this case, the entire probability is based on uncertainty. Most of the time however, the forecast probability covers both uncertainty and areal coverage. The first choice in this poll is only correct some of the time...and that is when areal coverage is the only factor, and not uncertainty. The third choice should always be correct if the forecast is accurate...it should rain at any specific point in the forecast area 6 out of every 10 times the forecast has a 60% chance of rain.
An interesting explanation on the subject:
http://www.crh.noaa.gov/riw/forecast/forcast_def.php
LOL, Man how did I copy the wrong selection, ignore my above post, I meant: if I had to choose I would have chosen: ("It will rain on 60% of the days like tomorrow."). The others are definitely wrong to me.
It will rain tomorrow in 60% of the area. I believe is wrong because usually a forecast is for a city or a section of a state, and if you say 60% area of a city or state section will get rain and the other 40% will not, is way too unsure or impossible to know.
It will rain tomorrow for 60% of the time. I believe this is wrong as well because is for the chance of rain, not the time frame or the amount of time it will rain that day. For example It can be a like a 30% or 40% chance of rain and sprinkle or rain most all of the day. Or it can be 60% and only rain hard for 2 hours.
It will rain on 60% of the days like tomorrow. This would be the best answer, though could be confusing, if all the conditions for rain chance that day are 60% then the other days that do not get rain but have the same conditions would be 40% of the time.
60% of weather forecasters believe it will rain tomorrow. This is obviously wrong, its about the chance of rain and not the weather forecasters. :-)
But I still like my other first post:
I put "other", and typed It would be a likely 60% chance of seeing rain that day, and a 40% of not seeing rain that day. That's how I've always looked at it, and I believe it's right. It's a chance, and the higher the percent the better chance you have of seeing at least some rain during that day. It's like spinning a percent pie wheel (60% rain/ 40% no rain), it's a game of probability.
I always thought a 60% chance of rain meant that there was a 6 in 10 chance of it raining in any one place.
Although I picked other and typed the above, if I had to choose I would have chosen: ("60% of weather forecasters believe it will rain tomorrow"). The others are definitely wrong to me.
I put "other", and typed It would be a likely 60% chance of seeing rain that day, and a 40% of not seeing rain that day. That's how I've always looked at it, and I believe it's right. It's a chance, and the higher the percent the better chance you have of seeing at least some rain during that day.
I have actually heard it been said two different ways in my classes. In fact, some Meteorologist incorrectly use the percentage forecast so much so that other Meteorologist refuse to even use the precentage tool as a means of explaining the expected rain chances. Some Meterologist just use the scattered/isolated terminology and leave it at that.
I think I have heard it been said more than once though that the answer is actually number 1 (first choice). I can understand the confusion but I still think suggesting a percentage in forecasting precipitation is very important.
It's scary to see how people can read all these different scenarios and still can't come up with the correct answer using COMMON SENSE!!! I should have been a meteorologist! The correct answer is option #3!
I understand the 1st answer to be the correct answer. But i believe that it should be that we should rain 60% of the day.
i can't believe that the first choice is winning!