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The most humorous part to me is when it says it's currently raining or snowing and it's clear and sunny. How can a system be so wrong that it can't tell the cur

The most humorous part to me is when it says it's currently raining or snowing and it's clear and sunny. How can a system be so wrong that it can't tell the current state of the weather?

bumby 3y ago
From the article: >”These observations are then fed into numerical prediction models to forecast the weather.” In other words, the forecasts come from models, not necessarily real-time station readings. Those readings are inputs into the model, and the models may not get updated fast enough to reflect current conditions.
- Fomite 3y ago
  Or it might be raining at the station the reading is being made at, but not where you are. Living in the west for example, a lot of weather stations are remarkably broad in the area they're expected to represent.
  - bumby 3y ago
    The point is that the forecasts are often not built from real-time weather station data, but models using various initial conditions.
ako 3y ago
Forecast are usually for a larger area, 5x5 kilometers, or 10x10 kilometers. Even within this area, weather will not be the same everywhere, so they'll give a probability for the entire area. Windy.com lets you compare different models for a specific location, it also includes the size of the area per model: https://www.windy.com/?49.339,5.054,5 https://www.windy.com/?49.339,5.054,5 GFS is area is 22km, ECMWF 9km, ICON-D2 2.2Km, Arome 1.3Km, and UKV is 2Km. Even in a 1.3x1.3Km area it may not rain everywhere at the same time. And then there's also the time element, so it's 1.3Kmx1.3Kmx1Hrs (or 3Hrs). So lot's of variation possible.
- amarcheschi 3y ago
  Yup, a few days ago I made a python script to help me choose whether to get to uni by bike or by moped when it rains (given two coordinates I calculate the angle(bearing?) and checks whether it rains, and the angle from which the wind blows to see if I'll get all wet in the face) and I had a bit of a hard time figuring out why two different providers, windy and openweathermap, gave me 2 different wind results. Eventually, I found out they were using a different model, it took a bit of time tho, because windy only has increments of hours, while the other one was more granular
counters 3y ago
Do you want a snarky answer or a serious answer? The serious answer is that the way you'd try to figure this out is by combining weather radar, satellite imagery, and a nearby surface observation to try to estimate the current conditions. But there can be a latency of up to a few minutes from these sources, and they could disagree with one another. You have to use them to bootstrap your near-term or nowcast product, but enforcing consistency with recent real-time and the nowcast is quite hard. It's a surprisingly nuanced technical challenge. Most of the time, it works out just fine (e.g. if there is no weather). But people are awfully good at remembering when these sorts of analyses end up being wrong!
- jrockway 3y ago
  Yeah. Like you would think you could just look at reflectivity data to determine whether or not it's currently raining, but at most places you are far from a radar site and even the 0.5 degree tilt is scanning a mile above your head. There might be rain there, but is it reaching the ground? All you can really do is guess. If you're interested in providing on-the-ground condition reports, install mPING: https://mping.nssl.noaa.gov/ https://mping.nssl.noaa.gov/ I keep this app on my homescreen and try to report when very light rain starts, since it's not always obvious from the reflectivity data. Ultimately the user reports get fed into things like improving the model, and more data is always good.
- avar 3y ago
  Apple devices are constantly phoning home every time they see a random AirTag out in the world. You'd think that if their users are accepting that level of communications with the mothership that they could ship some AI model to hear rainfall in the wild, and thus improve their live weather data.
  - counters 3y ago
    Surprisingly low signal-to-noise ratio for most of the common, creative ways people come up with to detect rain. Windshield wipers on cars are another example. The thing is, even if you did have a super reliable in situ "rain detector", how do you combine it with the existing datasets like weather radar, which is a gridded product? This is actually a really, really difficult sensor fusion problem when you then super-impose product requirements like the general location real-time detection map and the inputs necessary for whatever internal nowcasting system they use.
Etheryte 3y ago
I can't even begin to count how many times I've had this conversation with Siri. "Hey Siri, is it going to rain?" "It doesn't look like it's going to rain today." "It's raining right now." "It isn't raining right now."
- lotsofpulp 3y ago
  Why would you expect Siri to know if it is raining at your specific location? Surely there exists an edge where on one side it is raining and on the other it is not raining. So unless you are sitting next to the the weather station that Siri is getting data from, I would not expect it to know 100% of the time.
  - Etheryte 3y ago
    I live in the Netherlands. The local weather apps tell me when it's going to rain with nearly minute precision, along with cloud maps with scrollable time, graphs of how heavy the rain will be at what time, etc. It's pure nonsense to claim this is a technical limitation when other apps do it with ease. No one is expecting it to be right 100% of the time, but Apple Weather is wrong about rain most of the time, even on a crude scale of say, a city.
    - deleted 3y ago
      [deleted]
  - ceejayoz 3y ago
    > Why would you expect Siri to know if it is raining at your specific location? I don't, but as a result, I expect it not to guess.
    - Filligree 3y ago
      But you’re asking it to guess, and it’s usually right. Surely that’s better than having it refuse to offer a suggestion.
- 3y ago
NikkiA 3y ago
Because the 'current' weather isn't, it'll be whatever the last update of your chosen weather station reported. Often people choose a generic station that can be quite far from where they actually are - my default if I allow weather sites to 'guess' tends to be the airport 14 km away and 200m higher than me. A lot of weather can pass me by and still not have gotten to the airport in the 40 minutes since the last update.

The most humorous part to me is when it says it's currently raining or snowing and it's clear and sunny. How can a system be so wrong that it can't tell the current state of the weather?

bumby 3y ago

From the article: >”These observations are then fed into numerical prediction models to forecast the weather.” In other words, the forecasts come from models, not necessarily real-time station readings. Those readings are inputs into the model, and the models may not get updated fast enough to reflect current conditions.

Fomite 3y ago
Or it might be raining at the station the reading is being made at, but not where you are. Living in the west for example, a lot of weather stations are remarkably broad in the area they're expected to represent.
- bumby 3y ago
  The point is that the forecasts are often not built from real-time weather station data, but models using various initial conditions.

ako 3y ago

Forecast are usually for a larger area, 5x5 kilometers, or 10x10 kilometers. Even within this area, weather will not be the same everywhere, so they'll give a probability for the entire area. Windy.com lets you compare different models for a specific location, it also includes the size of the area per model: https://www.windy.com/?49.339,5.054,5 https://www.windy.com/?49.339,5.054,5 GFS is area is 22km, ECMWF 9km, ICON-D2 2.2Km, Arome 1.3Km, and UKV is 2Km. Even in a 1.3x1.3Km area it may not rain everywhere at the same time. And then there's also the time element, so it's 1.3Kmx1.3Kmx1Hrs (or 3Hrs). So lot's of variation possible.

amarcheschi 3y ago
Yup, a few days ago I made a python script to help me choose whether to get to uni by bike or by moped when it rains (given two coordinates I calculate the angle(bearing?) and checks whether it rains, and the angle from which the wind blows to see if I'll get all wet in the face) and I had a bit of a hard time figuring out why two different providers, windy and openweathermap, gave me 2 different wind results. Eventually, I found out they were using a different model, it took a bit of time tho, because windy only has increments of hours, while the other one was more granular

counters 3y ago

Do you want a snarky answer or a serious answer? The serious answer is that the way you'd try to figure this out is by combining weather radar, satellite imagery, and a nearby surface observation to try to estimate the current conditions. But there can be a latency of up to a few minutes from these sources, and they could disagree with one another. You have to use them to bootstrap your near-term or nowcast product, but enforcing consistency with recent real-time and the nowcast is quite hard. It's a surprisingly nuanced technical challenge. Most of the time, it works out just fine (e.g. if there is no weather). But people are awfully good at remembering when these sorts of analyses end up being wrong!

jrockway 3y ago
Yeah. Like you would think you could just look at reflectivity data to determine whether or not it's currently raining, but at most places you are far from a radar site and even the 0.5 degree tilt is scanning a mile above your head. There might be rain there, but is it reaching the ground? All you can really do is guess. If you're interested in providing on-the-ground condition reports, install mPING: https://mping.nssl.noaa.gov/ https://mping.nssl.noaa.gov/ I keep this app on my homescreen and try to report when very light rain starts, since it's not always obvious from the reflectivity data. Ultimately the user reports get fed into things like improving the model, and more data is always good.
avar 3y ago
Apple devices are constantly phoning home every time they see a random AirTag out in the world. You'd think that if their users are accepting that level of communications with the mothership that they could ship some AI model to hear rainfall in the wild, and thus improve their live weather data.
- counters 3y ago
  Surprisingly low signal-to-noise ratio for most of the common, creative ways people come up with to detect rain. Windshield wipers on cars are another example. The thing is, even if you did have a super reliable in situ "rain detector", how do you combine it with the existing datasets like weather radar, which is a gridded product? This is actually a really, really difficult sensor fusion problem when you then super-impose product requirements like the general location real-time detection map and the inputs necessary for whatever internal nowcasting system they use.

Etheryte 3y ago

I can't even begin to count how many times I've had this conversation with Siri. "Hey Siri, is it going to rain?" "It doesn't look like it's going to rain today." "It's raining right now." "It isn't raining right now."

lotsofpulp 3y ago
Why would you expect Siri to know if it is raining at your specific location? Surely there exists an edge where on one side it is raining and on the other it is not raining. So unless you are sitting next to the the weather station that Siri is getting data from, I would not expect it to know 100% of the time.
- Etheryte 3y ago
  I live in the Netherlands. The local weather apps tell me when it's going to rain with nearly minute precision, along with cloud maps with scrollable time, graphs of how heavy the rain will be at what time, etc. It's pure nonsense to claim this is a technical limitation when other apps do it with ease. No one is expecting it to be right 100% of the time, but Apple Weather is wrong about rain most of the time, even on a crude scale of say, a city.
  - deleted 3y ago
    [deleted]
- ceejayoz 3y ago
  > Why would you expect Siri to know if it is raining at your specific location? I don't, but as a result, I expect it not to guess.
  - Filligree 3y ago
    But you’re asking it to guess, and it’s usually right. Surely that’s better than having it refuse to offer a suggestion.
3y ago

NikkiA 3y ago

Because the 'current' weather isn't, it'll be whatever the last update of your chosen weather station reported. Often people choose a generic station that can be quite far from where they actually are - my default if I allow weather sites to 'guess' tends to be the airport 14 km away and 200m higher than me. A lot of weather can pass me by and still not have gotten to the airport in the 40 minutes since the last update.