Talk:Probability of precipitation

Aug 2011
The definitions in this article do not adequately explain the way public weather services, such as weather.com, report POP. They typically assign a POP to a date, and also assign a POP to each individual hour. You might think the former uses a 24 hour period and the latter a 1 hour period, but the values reported make that implausible. Often one or more hourly POPs are the same as the 24 hour POP. This would imply unnatural correlations among the hours. 184.96.5.102 (talk) 14:22, 14 August 2011 (UTC)

Still some confusion about the definition
Looking at the current text, it says:


 * So, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. The NWS explains this as follows: "Chance of rain 40 percent" means there is a 40 percent chance that rain will occur at any given point in the area. Another way to express "Chance of rain 40 percent" is that on average for all of the points in the area during the specified time period (usually 12 hour periods), chance that rain will occur (on average) is 40%.

Perhaps what it should say is this (chnages in bold):


 * So, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. The NWS explains this as follows: "Chance of rain 40 percent" means there is a 40 percent chance that rain will occur at any given point in the area at any given time. Another way to express "Chance of rain 40 percent" is that on average for all of the points in the area during the specified time period (usually 12 hour periods), chance that rain will occur it will be raining at any given moment (on average) is 40%.

But it would be good if someone could confirm that. Also, since the article says that there are alternative competing semantics in use, the article should be clear about all of them. -- pde (talk) 18:02, 10 September 2011 (UTC)


 * This explanation makes little sense, logical or practical. "For instance, if there is a 100% probability of rain covering one side of a city, and a 0% probability of rain on the other side of the city, the POP would be 50%."


 * Hello? A person about to be precipitated on has to be on one side of the city or the other. You therefore cannot average the rainfall probabilities according to position (unless he was small enough to be under the influence of quantum mechanics).


 * A "40% chance of rain" should mean that, whenever the current set of meteorological conditions occurs, it will rain 40% of the time. What else should it mean? WilliamSommerwerck (talk) 13:28, 9 June 2013 (UTC)


 * Hi William -- it does make sense, because although the walking individual certainly knows which side of the city they are in, the metereologist making the forecast does not. If the meteorologist were literally making a forecast tailored to the single individual in question, then you would have a good point. But that isn't the case -- there is a practical limit to how small an area the meteorologist can make predictions about. For that matter, suppose you are reading a forecast today for tomorrow and you yourself are not sure which part of the city you will be in tomorrow. Probability is all based around the information that is known by the individual making the prediction at the time they are making the prediction, NOT any information that is known by anybody else or becomes known at any time after. D. G. 03:52, 21 December 2013 (UTC)

Ok so, THE PERCENT OF PRECIPITATION IS THE CHANCE OF IT RAINING, HAILING, SLEETING OR SNOWING! so, a 95% chance of precipitation means you should prbably bring along an umbrella. Edona23456 (talk) 01:46, 2 March 2017 (UTC)

May 2012
The following relateds to a comment placed in thre article by an IP editor. Melcombe (talk) 21:15, 11 May 2012 (UTC)

After ...

The mathematical definition of Probability of Precipitation is defined as:


 * $$\text{PoP} = C \times A$$


 * C = the confidence that precipitation will occur somewhere in the forecast area.
 * A = the percent of the area that will receive measurable precipitation, if it occurs at all.

...the editor put the following comment...

(Should this not include some consideration of the time period? I often see a daily forecast indicating e.g. 30% chance of precipitation, yet when I look at the hour by hour forecast they all say 30% too.  If the chance of rain in each hour of the day is 30% then the chance of no rain over the 24 period is 0.7^24, that's 0.0002.  i.e. it's almost certain to rain.  This would not appear to be the message that the forecaster is trying to get across).
 * Both are incorrect. The article is poor, the definitions ignore the correlation problems. — Preceding unsigned comment added by 109.186.244.207 (talk) 08:34, 18 February 2021 (UTC)

Dead Link
the link for http://www.nws.noaa.gov/forecasts/graphical/definitions/definePoP12.html is dead. I found a new link to the same content at http://www.srh.noaa.gov/jax/?n=probability_of_precipitation — Preceding unsigned comment added by 129.33.49.252 (talk) 19:34, 3 July 2012 (UTC)

Drizzle or Flood
I really miss some indication of how heavy rainfall might be - a drizzle or should I start building an ark?24.5.61.77 (talk) 02:01, 6 March 2016 (UTC)

I just want the general public to understand the Percentage of percentage.
Meteorologist/Weatherman: "The chance of Precipitation is 95% today in Phoenix, AZ so bring an Umbrella and Good Luck!"

General public: "Pfft, everyone knows that Idiot!" (Meanwhile you are on wikipedia for a reason.)

Ok so all of these people are acting so smart and adding so much more to this than there actually is, let me put this simple and to the point for you. The chance of Precipitation is the Chance of Rain, Snow, Hail or sleet.. Nothing to do with Location or the fact that you are on one side of the city, and they are on the other so they wont be rained on. Now that that is out of the way, Is the Weatherman so smart now? - Edona Edona23456 (talk) 01:55, 2 March 2017 (UTC)

Removed claim about independence of hourly presence of thunderstorms
I have removed a part of the article that claimed that the hourly presence of thunderstorms is independent, along with reasoning that relied on this. The claim is clearly false and misleading. (For example, the presence of clouds is highly correlated from one hour to the second, due to how clouds move geospatially. Clouds are a precondition to thunderstorms.) --160.39.13.0 (talk) 22:56, 28 February 2021 (UTC)

Not helpful article for general public
I’m here because I’m reading a PoP of 50% for snow in a situation where snow or not snow really matters. Think “Wikipedia will clear up my confusion”. nope. Could someone please provide a plain English explanation for us idiots? Jennpublic (talk) 04:32, 31 December 2023 (UTC)