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I sometimes wonder about two things: Will it rain in my city? If so, when?

Please teach me the best way to find answers.


Please don't point me to the local weather services' "hourly forecasts". They're too vague for me to completely understand, as detailed in the small print below.

My government's weather service is called Environment Canada. They publish a probability of precipitation (POP) when the likelihood of rain or snow is "maybe". They say it's the "chance that measurable precipitation [...] will fall on 'any random point of the forecast region' during the forecast period". This is confusing. But, taken together with the relevant Wikipedia article, it's understandable.

Some other weather services offer "hourly forecasts" for my city. But I don't understand their stated POPs. I did a Google search which led me to a post by Trigonal Planar. Here's a Trigonal Planar quote which I have modified to reflect my current guess at what hourly POPs mean. "The chance of rain [during] a particular [period] is 20%. But during the [period], certain hours are more or less prone towards producing said rain." This is still too confusing.

So, if you point me to a weather-forecast website, please point me to one where I can find a clear definition of each included element.

(Related question: Will it snow in my city? If so, when, and how much?)

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4 Answers 4

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Use the moisture radar, it's your best tool to see when the rain is coming and when it's going with great detail. If you take the time to familiarize yourself with it you'll start to get a feel for how different types of rain look on the radar and where it's going to hit.

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I agree. If you go to weatheroffice.gc.ca/radar/index_e.html?id=WKR for example, then click on the [>] (play) button top left of the image: you'll see the speed and direction at which rain is moving towards you. –  ChrisW Nov 11 '12 at 13:28
Yeah, if you're interested in the next couple of hours you should look at the radar (use the "loop" version) and see which way the weather is moving. Any "prediction" off the web will be a general one for hundreds of square miles, and won't be specific to your location. –  Daniel R Hicks Nov 11 '12 at 13:36
But: @DanielRHicks: "Terminal aerodrome forecast" on Wikipedia says, "TAFs apply to a 5-mile (8 km) radius from the center of the airport runway complex." Dear all: 1. I live 12 miles (20 km) away from my local airport, so I suspect TAFs are fairly accurate even for me. 2. TAFs are written by experts. 3. I assume the experts look at more data than just a radar image loop. 4. I'm no expert. Given these four points, am I really better off ignoring the experts and predicting the weather myself? –  unforgettableid Nov 14 '12 at 21:12
If you find out how to predict where it's going to rain 16 hours from now you should hurry to the patent office. –  hillsons Nov 14 '12 at 23:06
All a TAF or any other forecast 5-8 hours out will be able to tell you is probabilities. Looking at radar I can estimate pretty well that, say, a band of rain will come through in 20 minutes, last 10, and then there will be dry weather for the next 30. This is the sort of info that's useful if you want to know it it's a good time to leave work, eg. For longer periods -- more than an hour or two out -- you just have to play the probabilities, though. –  Daniel R Hicks Nov 15 '12 at 1:30

If you use an iOS device, I use an app called Aero Weather (there is a free version, but I liked it enough to show support for the developer and paid for the Pro version).

This shows the various feeds available from many airports, runways, aerodromes and other similar sites. You can show the summary of 4-5 airports on an iPhone screen - more than enough to get a quick overview of local conditions.

It shows current readings, but you're able to drill in to their forecasts. As others have said, the airport analyses tend to be written by experts so is credible, but the readings are also frequently updated.

For my commute/training rides, I have a local list of various airports within 20-30 miles of home so I can get an instant picture of how the wind/temperature/cloud and so on is differing in the various directions.

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My city contains a large airport. I've discovered that some weather services provide terminal aerodrome forecasts (TAFs) for that airport, and that TAFs are well-defined. Some websites that provide TAFs include:

  • CheckWX. The easiest to use. (For a demonstration, go here and click the "Forecast" tab.)

  • The US NOAA Aviation Weather Center. My favorite. Enter an aerodrome code, click "Translated", then click "Get TAFs". (For a demonstration, go here.)


  • The demonstration links I provided are for London Heathrow airport. It's very rainy there, so the forecasts can be confusing. Alternatively, try checking the forecast for a less-rainy aerodrome: e.g. KDEN, KBOS, or KORD.

  • A "Temporary" or "Probable" group can modify the group that precedes it.

  • All times mentioned in TAFs are UTC, not local time.

  • Mist is a type of fog, not a type of rain.

  • All the elements in an American TAF are defined in an article entitled "TAF Decoder".

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I personally use Yahoo weather service as I have found it the most reliable for hourly predictions.

Try this.

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Thank you for trying to help. But like I said in my question, hourly forecasts confuse me. I don't quite understand their stated POPs. That's why I switched to using terminal aerodrome forecasts in the first place. Please don't just point me to yet another hourly-forecast site. -1. –  unforgettableid Nov 14 '12 at 18:46
In my experience, hourly forecasts are surprisingly accurate considering they are predicting the future. Sorry for trying to be helpful. –  jamiethepiper Nov 14 '12 at 19:31
Please read my question again. I wrote, "Where can I find a detailed weather forecast for my area, plus a clear definition of each included element?" The site you mention in your answer does provide a detailed forecast. But it does not provide any definition of any included element. –  unforgettableid Nov 14 '12 at 20:41
I take your point, just offering my opinion. –  jamiethepiper Nov 14 '12 at 23:45

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