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Modern Weather Forecasts Are Stunningly Accurate

theatlantic.com

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Re: Modern Weather Forecasts Are Stunningly Accurate

#61

Post by Majromax »

nonsequitter wrote: post #47
organsnyder wrote: post #37

Earlier quoted context omitted.

Weather ≠ climate.

right. climate is a more complex system. more variables. more unknowns. exponentially larger prediction area. unknown base states. so it should be much easier to predict right?

> so it should be much easier to predict right?

Yes, because the goals of the forecast are different. A weather forecast seeks to predict a future position within the phase space of the system; a climate forecast seeks to predict the overall shape of that phase space.

"It will be 1C warmer in February on average" is a useless prediction if I'm deciding whether or not to wear a heavy coat tomorrow, since day-by-day variability swamps that average. But it is a very useful prediction if I'm designing infrastructure that needs to last 50 years.

Re: Modern Weather Forecasts Are Stunningly Accurate

#62

Post by Majromax »

voyager2 wrote: post #35

I use the forecast put out by weather.gov that's supposedly tailored to the square mile because it gets the 12 hour forecast right about 40% of the time. The others are worse. Of course, when they say "chance of precipitation is 80%, less than an inch possible" and it doesn't rain, the forecast is semantically "correct." Like the El Nino impact on the SE US, where they forecast a 50% chance of drier colder weather an…

> I use the forecast put out by weather.gov that's supposedly tailored to the square mile because it gets the 12 hour forecast right about 40% of the time.

Unfortunately, this is an example of false precision. The highest resolution numerical forecasts run by NOAA have a grid of about 3km, already coarser than your one-square-mile "tailored" output. The effective resolution of numerical weather models is also 2-3 times coarser than their grid spacing (because of numerical diffusivity and similar effects).

What you're seeing isn't a "tailored" output, but instead an interpolated result from a coarser grid.

Forecasting of very high-resolution effects is the subject of active and ongoing research, but unfortunately popular meteorology does not do a good job of discussing current limitations.

Look at the confusion in this set of comments, for example, about what degree of forecast error is normal/acceptable.

Re: Modern Weather Forecasts Are Stunningly Accurate

#63

Post by voyager2 »

Majromax wrote: post #62
voyager2 wrote: post #35

I use the forecast put out by weather.gov that's supposedly tailored to the square mile because it gets the 12 hour forecast right about 40% of the time. The others are worse. Of course, when they say "chance of precipitation is 80%, less than an inch possible" and it doesn't rain, the forecast is semantically "correct." Like the El Nino impact on the SE US, where they forecast a 50% chance of drier colder weather an…

> I use the forecast put out by weather.gov that's supposedly tailored to the square mile because it gets the 12 hour forecast right about 40% of the time. Unfortunately, this is an example of false precision. The highest resolution numerical forecasts run by NOAA have a grid of about 3km, already coarser than your one-square-mile "tailored" output. The effective resolution of numerical weather models is also 2-3 tim…

If I move my forecast location a few hundred yards, my elevation changes rather drastically, changing the forecast. Elevation isn't a factor most forecasts even consider. Is it false precision to use elevation to tailor the forecast?

Re: Modern Weather Forecasts Are Stunningly Accurate

#64

Post by chaosbutters »

saagarjha wrote: post #4

> In 2009, a back-of-the-envelope study estimated that U.S. adults check the weather forecast about 300 billion times per year. That's every single adult in the United States checking the weather four times a day . A bit more than I would have expected…

December-April, I check a few times a day and different sources for snow/ice since I do not feel comfortable driving and getting caught in it. The number of times increases especially if I'm traveling. So when you time-average this over the year, it makes more sense.

Re: Modern Weather Forecasts Are Stunningly Accurate

#65

Post by grawprog »

jacques_chester wrote: post #46

Many folks, when hearing forecasts have improved, will disagree. They can think of many times when the forecast was wrong, perhaps hilariously or disruptively so. This is textbook availability bias. You overestimate the failure rate because the failures were memorable, especially the major failures. But the far more frequent accurate predictions are not recalled, because they don't leave as much of an emotional impre…

I worked outside every day for 4 years at least. Weather forecasts are so unreliable I stopped listening. I had better luck trying to figure out if i'd need rain gear in a day by just waking up and looking out the window in the morning than looking up or listening to a weather forecast.

You really start to notice how wrong they are when you spend every day outside. I don't notice any more working inside again. But when you rely on weather forecasts everyday to figure out how miserable you're going to be in a day...you really notice..they might as well just be making things up half the time.

Re: Modern Weather Forecasts Are Stunningly Accurate

#66

Post by simonh »

sleepysysadmin wrote: post #55

The recent snow storm in my area, 4 days in advance they were predicting 30cm of snow. 3.5 days in advance were 25cm of now. 3 days in advanced 15cm of snow. 2 days in advanced 5-10cm of snow. 1 day in advance 15cm of snow. We got about 10cm of snow. Sorry but that's stunningly inaccurate.

4 days in advance they correctly predicted you would get snow and that it would be on the order of tens of centimeters thick. That's really good. Over the intervening days they revised their estimate down and the snowfall was eventually lower than the initial estimate so the accuracy improved. Their final estimate was again correct that you did get snow, which is the key prediction, and they even got the depth at your precise location right to within 33%. That's fantastic, and far better than was possible for the vast majority of my lifetime.

Also, the fact that their predictions were all rounded to the nearest 5cm should give you a clue at the expected accuracy and granularity of the final prediction. Missing the target by only one 'unit' of measure is pretty decent.

Re: Modern Weather Forecasts Are Stunningly Accurate

#67

Post by firebird84 »

saagarjha wrote: post #4

> In 2009, a back-of-the-envelope study estimated that U.S. adults check the weather forecast about 300 billion times per year. That's every single adult in the United States checking the weather four times a day . A bit more than I would have expected…

When there's a hurricane incoming during the season, I check more often than that, at least every time the NHC has a new advisory. I imagine severe weather events cause huge surges in activity, it's probably not normally distributed throughout the year.

Re: Modern Weather Forecasts Are Stunningly Accurate

#68

Post by accuranalysis »

jacques_chester wrote: post #46

Many folks, when hearing forecasts have improved, will disagree. They can think of many times when the forecast was wrong, perhaps hilariously or disruptively so. This is textbook availability bias. You overestimate the failure rate because the failures were memorable, especially the major failures. But the far more frequent accurate predictions are not recalled, because they don't leave as much of an emotional impre…

ForecastWatch, a company solely dedicated to analyzing the accuracy of weather forecasts, has a good study available: https://www.forecastwatch.com/wp-content/uploads/High_Temper...

You can also check accuracy for your local zip code (in US) at: https://www.forecastadvisor.com/

tldr: for the best US consumer weather forecasters the mean error on high/low temp for 1-5 day forecasts is around 3F and they hit within 3F within 70% of the time.

7-day has declining accuracy and 10-day is not much better than statistical analysis on historical trends.

Re: Modern Weather Forecasts Are Stunningly Accurate

#69

Post by plopz »

jacques_chester wrote: post #46

Many folks, when hearing forecasts have improved, will disagree. They can think of many times when the forecast was wrong, perhaps hilariously or disruptively so. This is textbook availability bias. You overestimate the failure rate because the failures were memorable, especially the major failures. But the far more frequent accurate predictions are not recalled, because they don't leave as much of an emotional impre…

You can use this site to compare the different models using statistics.

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/

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