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Comment by magicalhippo | Hacker News Reader

I had been very disappointed with the local weather forecast last summer, and then there was an interview with one of the meteorologists involved and they said they were quite proud of how accurate their predictions had been so far. I was taken aback, as in my mind their "success rate" had been well below 50%.

Then I got my answer: they focused on the temperature forecast, while since I bike to work what I was interested in was "is it gonna rain today?"

I get that it's difficult to predict when and where rain might occur, but I'd much prefer a rough probability scale to nothing. On the bright side, they have a real-time, radar-based 90 minute rain forecast now, so at least if I check it in the afternoon I can jump on my bike and get home before I get wet.

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I think part of the problem is not the accuracy of the forecast, but whether it's useful to you, or not.

As an example, they may forecast that 30% of the areas your city will report rain tomorrow. They may have an high level of confidence in this prediction (and verify it to be correct after the fact). It may still not be very useful to you, since the one outcome is so different to the other.

That said, I agree with your that the predictions should be presented in a more scientific manner. In fact, one irritating pattern is that rain probability and the predicted amount of rain sometimes get combined into a single percentage, which no longer represents neither the probability, nor the amount. It's some kind of weird combination of the two.

Yeah, here they report rain just in mm. They might say 3-7.3mm, or they might say 0-4mm. Now I don't care too much about 2.5mm or 6.1mm, but I definitely care about the chance of more than light rain. For others, people with a gardens etc, the amount of water might matter more.

Just last Thursday they reported zero precipitation for the entire day, not a hint of rain. Yet we got 3 hours of medium-heavy showers in the afternoon... not a very uncommon combination. If I had known there was a 30% chance of showers, I would have packed my rain jacket.

From talking with meteorologists, it seems forecasting actual rain is not very hard if you have enough current data on the state of the atmosphere. What can be difficult is mistiness that is just on the borderline between falling droplets and moisture just hanging in the air. Differences can be extremely local in nature. [I'm not a meteorologist, I program computers, but I'm a pilot so I have a pilot's appreciation of and contact with weather.]

Or even the proportion and impact of ice v. water droplets. The modelling of this in a warming world is making the latest global climate models used in the upcoming IPCC AR6 show a higher equilibrium climate sensitivity than the previous edition [0].

[0] http://www.realclimate.org/index.php/archives/2020/06/sensit...

Hi geoff - seems like you are pretty knowledgeable here. I have to disagree with "seems forecasting actual rain is not very hard if you have enough current data on the state of the atmosphere" ... Who told you that? accuweather meteologists?

Rain is not easy predict, especially long in advance. Just taking things with a grain of salt here. If you truly believe that forecasting actual rain is not very hard, please start a new weather forecasting company and give it all you got! However i'll tell you, it's not that easy. Just because a computer model 'runs' does not mean it correctly modeled the atmosphere. All models are imperfect bud and those imperfections get amplified by 10x when trying to simulate earth+atmosphere systems

No, I'm not especially knowledgeable, not more than others here. As a pilot, I have 42 years of experience flying through weather and helping get the word out w/r/t hurricanes, e.g., relaying info via ham radio in the West Indies from relays in Florida before getting hit by the storms, back in the 1970s when that was the way, so I have long interest in and appreciation of weather. But I do also have appreciation for my colleagues and their meteorological expertise. They have something called MinuteCast which in my experience has been very accurate in telling me when precipitation will begin or end (except when it is misty). Regarding my "forecasting actual rain is not very hard" remark, you are right that a "long in advance" forecast is hard, but I was talking about the short term. Specifically, a commenter had wanted to know if it was going to rain before going out to exercise, and for that example, I meant a forecast of precipitation was easy.

I believe accuracy may have dropped due to the decreased number of flights collecting data, but Dark Sky in years past has been very effective at forecasting rain. I rely heavily on it since I typically go most of the summer without a top on my Jeep.

I think you will like the new app coming out next month better, especially with your use case.

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