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Comment by chewz | Hacker News Reader

Just follow few models for a couple of weeks and you will notice how inaccurate the weather forecast is.*

I do follow ECMWF and ICON and a bit of OpenWeather forecast and the differences in forecasted temperatures are often 2-3 degrees C. And everything with a horizon over 72 hours is just numerology. (OpenWeather showed -19C in early days of Feb just 2 days ago, today it is -2C).

Now a model is just a model (I had some experience with industrial and financial models) so they are good at this and not so good at that. And they are recalculated and self-adjusted over time. I can understand.

But from the user perspective there is huge difference between +1C tomorrow and -3C.

Windy app is using 4 models and has nice graphical comparision of forecasts.

* - What I mean here is that meteorologists have good understanding of processes but the numbers that we are getting could be as well random.

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The article discusses a scientific paper that has tried to quantify the accurateness of the forecasts, and you just hand-wave that away with your own anecdotes?

But from the user perspective there is huge difference between +1C tomorrow and -3C.

Really? I'd read those both as "near freezing, going to need a decent coat".

If they're both relatively rare for you you might not notice a difference, but if you encounter them more often you'd notice I think.

+1 means that the packed snow is going to melt on top and then probably re-freeze, making everything super slippery. So I need to remove as much snow from the paths as possible and spread sand, and remind the kids to be careful.

-3 means relax.

The temperatures given are usually air temperatures. If the ground is warm enough -- which it is usually is in the cities -- then it doesn't really matter, the snow will melt in both cases.

Not here mate, not in one day that's for sure.

It is unfortunate for us that even tiny prediction misses around the freezing point have drastic differences in our experience. But it does not change that they are tiny prediction misses. We take for granted how good they have become.

Really. -3C is slippery roads and pavements. It matters if you walk or bike etc. But it is dry and feels warm. +1C is humid and feels cold.

The difference between +1 and 0 is the difference between me making the turn on my bicycle yesterday, and me sliding across the road on my side and then spending 15 minutes trying to fix the chain.

The windy.com site is really useful. It is the only way I know to get the ECMWF forecasts for free. As far as I know all the AccuWeather and similar spyware apps use the freely available but inferior GFS model.

There's a few places you can get ECMWF from, but usually your state meteorology institute will use it, even if it's not clearly advertised. (In Portugal they use ECMWF together with AROME)

weather.us as well, they even have the 50 different ensembles for the Euro. Very surprised it's free but I ain't complaining.

Tropical Tidbits is a more US focused site with an emphasis on tropical storm season (hence the name) but they keep the models running & updating all year.

oh man - you want to know something funny. At my startup we had a guy hacker in a random weather generator to use in our models. I was like WTF Man!

The numbers you are getting are not random. Sure the models are chaotic and non-linear, but still it's giving you hints at potential patterns, especially at long range time scales. People need to understand that wx forecasts, especially 3+ days out, should be read as guidelines for what is LIKELY to happen. Say that GFS predicts two inches of rain for your city over the next week as a wave comes through. What if the next model run shifts that blob of rainfall 25miles north? In the model terms, global terms, 25miles is nothing. But for you that is the difference between dry & soaked , and you think the model sucks.

Do you know where to get historical forecasts easily (to gauge accuracy)?

Windy's NEMS model is awesome for complex alpine terrain.

In Italy forecast are so unreliable they cannot predict rain in the evening from the morning.

I don't know if it's because current climate change is throwing off models but short term forecast accuracy is terrible and I'm recently acutely aware of that since I switched to public transport for my commute.

I know. I had been tending large garden (roses and lawn) in my friends house in Toscana this summer. And I had been looking for a rain everyday :-) and observing the change in forecasts and acctual result.

I've seen similar in California. Forecasts are really not always that accurate even within 24h.

This anecdotal, but I have observed, in my experience in Europe, that short-term forecasts are really inaccurate in countries like Belgium and Italy while, for example, they are really, really spot-on in mainland Poland. So, my guess is that it really depends on the kind of climate and, perhaps, on the impact of climate change in that area.

I would attribute that to the substantial Soviet investment in meteorology.

I would rather to some longer term static patterns especially in summer or winter on large plains in Poland vs more of an unpredictable sea climate in Belgium and Italy.

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