4 ms·

I really thought that this was going to be about the weather.

nullindividual 3y ago
Same, but in a human context, are mundane atmospheric events so far off today that error bars would have any practical value and/or potentially introduce confusion?
- NegativeLatency 3y ago
  For this reason I really enjoy reading the text products and area forecast discussion for interesting weather: https://forecast.weather.gov/product.php?site=NWS&issuedby=pqr&product=AFD&format=CI&glossary=1 https://forecast.weather.gov/product.php?site=NWS&issuedby=p...
  - doubled112 3y ago
    Anybody happen to know if there's anything more detailed from Environment Canada than their forecast pages? https://weather.gc.ca/city/pages/on-143_metric_e.html https://weather.gc.ca/city/pages/on-143_metric_e.html I really like that discussion type forecast.
- yakubin 3y ago
  Absolutely. 15 years ago I could reasonably trust forecasts regarding whether it’s going to rain in a given location 2 days in advance. Today I can’t trust forecasts about whether it’s raining currently.
  - Smoosh 3y ago
    It seems unlikely that the modelling and forecasting has become worse, so I guess there is some sort of change happening to the climate making it more unstable and less predictable?
    - lispisok 3y ago
      >I guess there is some sort of change happening to the climate making it more unstable and less predictable? I've been seeing this question come up a lot lately. The answer is no, weather forecasting continues to improve. The rate is about 1 day improvement every 10 years so a 5 day forecast today is as good as a 4 day forecast 10 years ago.
  - LexGray 3y ago
    I think that is a change in definition. 15 years ago it was only rain if you were sure to get drenched. Now rain means 1mm of water hit the ground in your general vicinity. I blame an abundance of data combined people who refuse to get damp and need an umbrella if there is any chance at all.
    - yakubin 3y ago
      No. I mean getting drenched, when forecast predicted no rain. 1mm isn’t really noticeable by humans.
- kqr 3y ago
  Sure -- just a few day outs the forecast is not much better than the climatological average -- see e.g. https://charts.ecmwf.int/products/opencharts_meteogram?base_time=202312041200&epsgram=classical_15d_with_climate&lat=59.3326&lon=18.0649&station_name=Stockholm https://charts.ecmwf.int/products/opencharts_meteogram?base_... Up until that point, error bars increase. At least to me, there's a big difference between "1 mm rain guaranteed" and "90 % chance of no rain but 10 % chance of 10 mm rain" but both have the same average.
  - jsmith45 3y ago
    The other thing is that many forecasts have a large range. So it might be that the left third of the forecast area has like a 99.9% chance of zero precipitation, the right third has a 99.9% chance of some precipitation, and there is some uncertainly about where the border will be, (and near the border might have less precipitation than the edge). The result is that I will be told ~50% chance of precipitation, but the places I care about might well be in the essentially 0% or essentially 100% parts. The single forecast for a decent size city problem impacts other parts like forecasted highs/low. Even without a front, in some cities that have incorporated much of their suburbs, it is not uncommon for the eastmost part and westmost part to differ by 5-6 degrees, and that is ignoring the inherent temperature differences found in the downtown areas.
dguest 3y ago
Me too, and I was looking forward to the thread that talks about error bars in weather models, which is totally a thing! It turns out the ECMWF does do an ensamble model where they run 51 concurrent models, presumably with slightly different initial conditions, or they vary the model parameters within some envelope. From these 51 models you can get a decent confidence interval. But this is a lower resolution model, run less frequently. I assume they don't do this with their "HRES" model (which has twice the spacial resolution) in an ensemble because, well, it's really expensive. [1]: https://en.wikipedia.org/wiki/Integrated_Forecast_System#Variants https://en.wikipedia.org/wiki/Integrated_Forecast_System#Var...
- lispisok 3y ago
  A lot of weather agencies across the world run ensembles including US, Canada, and the UK. Ensembles are the future of weather forecasting but weather models are so computationally heavy models have a resolution/forecast length tradeoff which is even bigger when trying to run 20-50 ensemble members. You can have a high resolution model that runs to 2 days or so or have a longer range model at much coarser resolution. ECMWF recently upgraded their ensemble to run at the same resolution as the HRES. The HRES is basically the ensemble control member at this point [1] [1] https://www.ecmwf.int/en/about/media-centre/news/2023/model-upgrade-increases-skill-and-unifies-medium-range-resolutions https://www.ecmwf.int/en/about/media-centre/news/2023/model-...
  - earthscienceman 3y ago
    I'm someone working in the field with weather modelers/forecasters but not a modeler myself. Reading this discussion has been an absolute treat ... The most fascinating thing about the concept of error in models, including in ensembles, is you can only calculate and propagate error for contributors that you can quantify. There are many unquantifiable sources of error. Imagine a physical process that you are unaware of that propagates as a bias, for example ice nucleation via aerosols. Perhaps you don't even model aerosols. How do you account for error here? What does error even mean? Ensembles only show you intramodel variability. Which is like error, sort of, but only really represents a combination of "real" variability in initial conditions and how that propagates through your physics/parameterizations. "models" the HN commentators make for their businesses surely have parallel concepts, but I don't see anyone talking about them. Only discussion about the errors you know when the ugliest errors are the ones that no one knows.
iruoy 3y ago
I've been using meteoblue for a while now and they tell you how sure they are of their predictions. Right now I can see that they rate their predictability as medium for tomorrow, but high for the day after. https://content.meteoblue.com/en/research-education/specifications/weather-variables/predictability https://content.meteoblue.com/en/research-education/specific...
- kqr 3y ago
  I'll give you one better. The ECMWF publishes their probabilistic ensemble forecasts with boxplots for numeric probabilities: https://charts.ecmwf.int/products/opencharts_meteogram?base_time=202311211200&epsgram=classical_10d&lat=59.3326&lon=18.0649&station_name=Stockholm https://charts.ecmwf.int/products/opencharts_meteogram?base_... They also have one for precipitation type distribution: https://charts.ecmwf.int/products/opencharts_ptype_meteogram?base_time=202312041200&lat=59.3326&lon=18.0649&station_name=Stockholm https://charts.ecmwf.int/products/opencharts_ptype_meteogram...

Same, but in a human context, are mundane atmospheric events so far off today that error bars would have any practical value and/or potentially introduce confusion?

NegativeLatency 3y ago
For this reason I really enjoy reading the text products and area forecast discussion for interesting weather: https://forecast.weather.gov/product.php?site=NWS&issuedby=pqr&product=AFD&format=CI&glossary=1 https://forecast.weather.gov/product.php?site=NWS&issuedby=p...
- doubled112 3y ago
  Anybody happen to know if there's anything more detailed from Environment Canada than their forecast pages? https://weather.gc.ca/city/pages/on-143_metric_e.html https://weather.gc.ca/city/pages/on-143_metric_e.html I really like that discussion type forecast.
yakubin 3y ago
Absolutely. 15 years ago I could reasonably trust forecasts regarding whether it’s going to rain in a given location 2 days in advance. Today I can’t trust forecasts about whether it’s raining currently.
- Smoosh 3y ago
  It seems unlikely that the modelling and forecasting has become worse, so I guess there is some sort of change happening to the climate making it more unstable and less predictable?
  - lispisok 3y ago
    >I guess there is some sort of change happening to the climate making it more unstable and less predictable? I've been seeing this question come up a lot lately. The answer is no, weather forecasting continues to improve. The rate is about 1 day improvement every 10 years so a 5 day forecast today is as good as a 4 day forecast 10 years ago.
- LexGray 3y ago
  I think that is a change in definition. 15 years ago it was only rain if you were sure to get drenched. Now rain means 1mm of water hit the ground in your general vicinity. I blame an abundance of data combined people who refuse to get damp and need an umbrella if there is any chance at all.
  - yakubin 3y ago
    No. I mean getting drenched, when forecast predicted no rain. 1mm isn’t really noticeable by humans.
kqr 3y ago
Sure -- just a few day outs the forecast is not much better than the climatological average -- see e.g. https://charts.ecmwf.int/products/opencharts_meteogram?base_time=202312041200&epsgram=classical_15d_with_climate&lat=59.3326&lon=18.0649&station_name=Stockholm https://charts.ecmwf.int/products/opencharts_meteogram?base_... Up until that point, error bars increase. At least to me, there's a big difference between "1 mm rain guaranteed" and "90 % chance of no rain but 10 % chance of 10 mm rain" but both have the same average.
- jsmith45 3y ago
  The other thing is that many forecasts have a large range. So it might be that the left third of the forecast area has like a 99.9% chance of zero precipitation, the right third has a 99.9% chance of some precipitation, and there is some uncertainly about where the border will be, (and near the border might have less precipitation than the edge). The result is that I will be told ~50% chance of precipitation, but the places I care about might well be in the essentially 0% or essentially 100% parts. The single forecast for a decent size city problem impacts other parts like forecasted highs/low. Even without a front, in some cities that have incorporated much of their suburbs, it is not uncommon for the eastmost part and westmost part to differ by 5-6 degrees, and that is ignoring the inherent temperature differences found in the downtown areas.

dguest 3y ago

Me too, and I was looking forward to the thread that talks about error bars in weather models, which is totally a thing! It turns out the ECMWF does do an ensamble model where they run 51 concurrent models, presumably with slightly different initial conditions, or they vary the model parameters within some envelope. From these 51 models you can get a decent confidence interval. But this is a lower resolution model, run less frequently. I assume they don't do this with their "HRES" model (which has twice the spacial resolution) in an ensemble because, well, it's really expensive. [1]: https://en.wikipedia.org/wiki/Integrated_Forecast_System#Variants https://en.wikipedia.org/wiki/Integrated_Forecast_System#Var...

lispisok 3y ago
A lot of weather agencies across the world run ensembles including US, Canada, and the UK. Ensembles are the future of weather forecasting but weather models are so computationally heavy models have a resolution/forecast length tradeoff which is even bigger when trying to run 20-50 ensemble members. You can have a high resolution model that runs to 2 days or so or have a longer range model at much coarser resolution. ECMWF recently upgraded their ensemble to run at the same resolution as the HRES. The HRES is basically the ensemble control member at this point [1] [1] https://www.ecmwf.int/en/about/media-centre/news/2023/model-upgrade-increases-skill-and-unifies-medium-range-resolutions https://www.ecmwf.int/en/about/media-centre/news/2023/model-...
- earthscienceman 3y ago
  I'm someone working in the field with weather modelers/forecasters but not a modeler myself. Reading this discussion has been an absolute treat ... The most fascinating thing about the concept of error in models, including in ensembles, is you can only calculate and propagate error for contributors that you can quantify. There are many unquantifiable sources of error. Imagine a physical process that you are unaware of that propagates as a bias, for example ice nucleation via aerosols. Perhaps you don't even model aerosols. How do you account for error here? What does error even mean? Ensembles only show you intramodel variability. Which is like error, sort of, but only really represents a combination of "real" variability in initial conditions and how that propagates through your physics/parameterizations. "models" the HN commentators make for their businesses surely have parallel concepts, but I don't see anyone talking about them. Only discussion about the errors you know when the ugliest errors are the ones that no one knows.

iruoy 3y ago

I've been using meteoblue for a while now and they tell you how sure they are of their predictions. Right now I can see that they rate their predictability as medium for tomorrow, but high for the day after. https://content.meteoblue.com/en/research-education/specifications/weather-variables/predictability https://content.meteoblue.com/en/research-education/specific...

kqr 3y ago
I'll give you one better. The ECMWF publishes their probabilistic ensemble forecasts with boxplots for numeric probabilities: https://charts.ecmwf.int/products/opencharts_meteogram?base_time=202311211200&epsgram=classical_10d&lat=59.3326&lon=18.0649&station_name=Stockholm https://charts.ecmwf.int/products/opencharts_meteogram?base_... They also have one for precipitation type distribution: https://charts.ecmwf.int/products/opencharts_ptype_meteogram?base_time=202312041200&lat=59.3326&lon=18.0649&station_name=Stockholm https://charts.ecmwf.int/products/opencharts_ptype_meteogram...