No Stupid Questions

Weather apps don't do real time analytics, but show you the forecast some nearby weather station has calculated. Whether that's based on current data or a couple hours ago depends on the exact provider they use. And hardly anyone of those are done by actual humans, it's aggregated statistics.

If you look at precipitation maps, you are doing that forecast by yourself based on cloud movements and local knowledge, something no machine-generated forecast can do as good.

Plus, there's usually one weather station covering a large area, so hyperaccurate predictions would have to be made just for you - which simply costs to much.

just because it knows where you are, doesn't mean it has measurement equipment there.

Just stand under the weather station, then it's exact

MinuteCast from AccuWeather does exactly this. It looks at your location, looks at radar data for storm systems approaching your location, and estimates when precipitation will start at your location and how intense it will be. It's generally pretty accurate, with some limitations. It seems to be pretty good for consistent rainstorms but it can get tripped up by pop-up thunderstorms, where the radar track can go suddenly from no rain to downpour. It doesn't make predictions more then 2-3 hours out because past that timeframe it's not easy to predict if weather will continue on its current track or change direction. Even with the limitations, I use it all the time. Mostly to tell if I should take the dogs out right away, or if I should wait an hour or two.

Weather prediction at point locations is extremely challenging to get right because we simply can't observe and make predictions for every single square inch of the earth. Many weather models are run on grids with boxes about the size of a few kilometers at the smallest scale, which means that any physical process in the atmosphere that is the size of that box or smaller won't be represented well by the model.

Specifically on your point about clouds passing over your location, cloud and precipitation formation is even more challenging. Clouds and precipitation form due to atmospheric processes ranging from hundreds of kilometers all the way down to micrometers, which practically means the weather models are making an educated guess (albeit a very good one that is informed by scientific research) about when and where clouds will form. And when a model does predict a cloud, it will cover an entire grid box.

Finally, I saw you made a comment about how machine learning should improve forecasts, and in fact it does! But the weather community is still working on data driven models (as opposed to models that solve physical atmospheric equations), and most of them are run by private companies so their output is not free. As these data driven models get better, it may be possible that they will be able to make predictions at scales less than a kilometer.

Darksky could do it back in the day more or less. you'd get messages that it would rain in about 15 minutes and stop in the next 30.

Thing is, precep maps don't work everywhere. You're probably in a location like me where a thick front rolling through will almost always bring rain. If you get into warmer tropical climates, rainclouds will just poof out of nowhere and drop rain on your ass while other crazy fronts will pass over with nothing but some dark clouds.

But a weather app on my phone has my exact GPS coordinates. Why can’t it tell me exactly when a rain cloud will be passing over my location?

Because they've never been able to do that...

When they say "50% chance of rain", it doesn't meant there's a 50/50 chance it rains where you're located

It's that for the broadcast area, about half is gonna get rain.

Look at a weather map with animated radar overlay. You will often see precipitation approaching and can predict how soon based on its speed and heading.

I know any in my case. I'm in a black hole of info. The nearest weather station is over 30 miles away and it's not remotely accurate for my location because of terrain changes between here and there. There isn't even a weather station in my overly large and oddly shaped county.

We went so far as to contact the people in charge of weather stations to see if we could set one up in our yard and while there was some initial excitement from them they eventually ghosted us.

NOAA sources are usually good in the US, weather.gov for a quick map and search by zip code or city, but they follow the same % system mentioned as most do

The couple apps/widgets I've tried haven't been good for working with VPN unless I want to know the weather halfway around the world.

For one thing, there's two competing weather services providing the data to countless apps in the US and one of them has more money to throw around than the other.

The weather channel has better weather predictions overall than Apple's own weather app, as rated by Forecastadvisor.com, but is not as accurate as Accuweather is although it's used in more apps.

Weather is about tracking and predictions. It's never going to be completely 100% correct. But taking a hodgepodge of information from several prediction services means you're more likely to be less accurate overall despite what people may think.

I went to Amsterdam over the weekend. The weather apps said it was gonna rain, did it fuck. I brought my puffer jacket and was almost dying from the heat until I got to the hotel room. Never had to wear it during the trip.

I just looked at my weather app (Today Weather), and the report of the current temperature varies by 6°F depending on which data set I choose. I go with the National Weather Service (federal govt).

As far as predicting precipitation, the radar seems pretty good for the next few hours. I press play on it, and it tells me what it thinks the radar will look like for the next 7 hours in 15 mins increments.

I think that predicting the weather beyond a day gets pretty difficult because the weather is too chaotic. The best they can do is to gather data from local weather stations and see how often it rained when they had these same data in the past. So basically, it's like saying, "When the temp has been 85°F, humidity 62%, wind from WNW at 5 kts, pressure at 1016 mBar, and the date was July 29, it rained 6 times out of 10."

Weather Underground allows you to filter down to your zip code. Not accurate down to your exact vicinity, but better than the weather forecast for your entire city.

I notice the rain predictions are quite a bit more accurate in the cooler months. You can see a weather front traveling west to east as it comes across the country (I'm in US) and rains can last all day. During the hotter parts in summer rain clouds appear out of nowhere usually in the afternoon and rains are heavy but brief. This happened here in NE Ohio just an hour ago. There was no forecast for rain that I was aware of but suddenly we got doused for twenty minutes.

Because we have tons of ground-level sensors, but not a lot in the upper layers of the atmosphere, I think?

Why is this important? Weather processes are usually modelled as a set of differential equations, and you want to know the border conditions in order to solve them and obtain the state of the entire atmosphere. The atmosphere has two boundaries: the lower, which is the planet's surface, and the upper, which is where the atmosphere ends. And since we don't seem to have a lot of data from the upper layers, it reduces the quality of all predictions.

The hourly forecast is mostly useless because it’s not a chance % but a % of the area that will be raining.

Unless your precise location is a statistical outlier these will be the same thing?