5 ms·

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

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 and a 50% chance of warmer wetter weather, it's nearly impossible to be wrong. Maybe this is the sort of obfuscatory probabilistic forecast Mr. Meyer is counting as "accurate."

kryogen1c 8y ago
No doubt. That's like saying horoscopes and fortune-tellers are stunningly accurate: "a positive opportunity will present itself to you today - you only have to open the door" "you are holding a secret pain that is preventing you from moving on. Find peace and let go"
maaaats 8y ago
> it gets the 12 hour forecast right about 40% of the time Where are these figures from? Your emotions, or something scientifically rigid? If the former, having this discussion is meaningless.
- deleted 8y ago
  [deleted]
- voyager2 8y ago
  "chance of precipitation is 80%, less than an inch possible" How would you determine, in a scientifically rigid manner, the limits on conditions which would validate that forecast as "right?" Or the inverse. What conditions would invalidate it as "not right?"
  - scott_s 8y ago
    In a top-level comment upthread, jacques_chester posted a link to an overview of forecast verification methods: http://www.cawcr.gov.au/projects/verification/ http://www.cawcr.gov.au/projects/verification/
Majromax 8y ago
> 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.
- voyager2 8y ago
  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?
  - Majromax 8y ago
    In that case, the interpolation includes a vertical component as well. You'll see the effects of the lapse rate (change in temperature with height). That's great for you, but it means that your forecast (of [my elevation, my coordinates]) is not much more accurate than one for ([my elevation, my coordinates plus a few hundred yards]). More technically: "surface" isn't a smooth variable when elevation changes quickly, but interpolation like that performed by weather.gov necessarily works on smooth fields. Applying post-facto elevation is great and worthwhile, but it doesn't improve the accuracy in a technical sense.

kryogen1c 8y ago

No doubt. That's like saying horoscopes and fortune-tellers are stunningly accurate: "a positive opportunity will present itself to you today - you only have to open the door" "you are holding a secret pain that is preventing you from moving on. Find peace and let go"

maaaats 8y ago

> it gets the 12 hour forecast right about 40% of the time Where are these figures from? Your emotions, or something scientifically rigid? If the former, having this discussion is meaningless.

deleted 8y ago
[deleted]
voyager2 8y ago
"chance of precipitation is 80%, less than an inch possible" How would you determine, in a scientifically rigid manner, the limits on conditions which would validate that forecast as "right?" Or the inverse. What conditions would invalidate it as "not right?"
- scott_s 8y ago
  In a top-level comment upthread, jacques_chester posted a link to an overview of forecast verification methods: http://www.cawcr.gov.au/projects/verification/ http://www.cawcr.gov.au/projects/verification/

Majromax 8y ago

> 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.

voyager2 8y ago
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?
- Majromax 8y ago
  In that case, the interpolation includes a vertical component as well. You'll see the effects of the lapse rate (change in temperature with height). That's great for you, but it means that your forecast (of [my elevation, my coordinates]) is not much more accurate than one for ([my elevation, my coordinates plus a few hundred yards]). More technically: "surface" isn't a smooth variable when elevation changes quickly, but interpolation like that performed by weather.gov necessarily works on smooth fields. Applying post-facto elevation is great and worthwhile, but it doesn't improve the accuracy in a technical sense.