Comments on: Why doesn’t the weather forecast have a confidence interval?

By: Steve

Steve — Wed, 24 Jun 2009 18:00:50 +0000

http://en.wikipedia.org/wiki/Weather_Rock

I also think that the National Weather Service should enlist the predictions of retired grandfathers for local regions throughout the country. I’d pay more attention to the forecast if it included statements like: “warm out today” or “squall’s a comin, I can feel it in me bones”

By: Charlie

Charlie — Tue, 23 Jun 2009 22:36:12 +0000

What a ferociously commented post. Tom Waits was right when he said “strangers talk only ’bout the weather; All over the world, it’s the same, it’s the same.”
Will, you have assembled a set of expert conversationalists.

By: 300baud

300baud — Tue, 23 Jun 2009 20:55:12 +0000

How is “looking” accurate or not relevant?

By: Franklin Evans

Franklin Evans — Tue, 23 Jun 2009 16:21:50 +0000

I am not a meteorologist, and with respect to those who are and who’ve posted so far, this is what I was told by a meteorologist years ago:

“Percentage chance” refers not to the event, but to the likely outcome of the conditions expected for the forecast period. (Over)Simplified, the basis for the calculation is the historical data for all days in the past that had closely similar conditions to those expected to occur, and the percentage value is the proportion of those days that actually had that outcome.

Personally, before any confidence adjustments, I’d rather see weather broadcasts remind the audience that forecasts are for fairly large geographical regions, well beyond the scope of most weather systems to affect in a manner consistent with the regional forecast. People will be less apt to conclude that meteorologists are incompetent if they understand that not every square mile of the region will experience the same things.

By: pyeager

pyeager — Tue, 23 Jun 2009 14:11:56 +0000

They probably convert the output directly from the computer models to make the tv graphics. These things are just as you said—too precise looking (but not literal) when traditional maps showing precipitation would give the public a better feel for the forecast.

By: pllatreille

pllatreille — Tue, 23 Jun 2009 13:34:20 +0000

You should try looking at the maps they use on the BBC TV weather forecasts these days – ’spurious accuracy’ if ever I saw it. Kind of like reporting a result to 3 decimal places – it may be wrong, but at least it’s *precisely* wrong (when approximately right would be better, certainly in a maritime climate)!! Lol.

By: pyeager

pyeager — Tue, 23 Jun 2009 12:29:11 +0000

I’m a meteorologist, with over 20 years of experience (my blog is cloudyandcool.com), and I’ve always believed that meteorologists should use fewer percentages, and a confidence level would only make the forecast more confusing–and make forecasters look even less accurate.

The government’s hurricane forecast (http://cloudyandcool.com/2009/06/18/2009-hurricane-season-forecast/) adds a confidence percentage to the forecast, with the result being a forecast of a 70% chance of 9-14 named storms. The range of storms already indicates uncertainty and adding a percentage to the forecast adds another level of uncertainty. They even apply the confidence level to their ACE, which is already a percentage estimate of the intensity of the season. The result is a forecast of a 70% chance of an intensity rating of 65%-130%. Tell me what that means–I have no idea how that could be useful.

I think people understand that a forecast is just that–a prediction of the future, with intrinsic uncertainty–so forecasters are better off taking a stand and issuing a more direct forecast rather than deliberately adding more uncertainty to the equation.

Paul Yeager (cloudyandcool.com)

By: Greg Laden

Greg Laden — Tue, 23 Jun 2009 11:29:38 +0000

This is not exactly true, but you COULD think of it this way and thus get to sleep at night.

The percentage given IS the confidence interval. The forcast is “It will rain” or “there will be a thunderstorm”

A near 100 percent ‘chance’ of a thunderstorm means “There will be a thunderstorm. Confidience interval = .02 p of being wrong (with a near 100 percent chance).” Or, “40% chance of rain today” means “It will rain today, p=0.6″

Again, this is NOT statisticaly what is happening, but it help you to feel better about it.

By the way, weather prediction as it is practices is not about chaos at all. Over meso- and macro-scales, weather may act in a chaotic way, but weather prediction is more about linear processes such as air movement and temperature, pressure, and humidity gradients.

By: Gus

Gus — Tue, 23 Jun 2009 10:23:11 +0000

The South African Weather Service shows the confidence % for each of there daily forecasts.

http://www.weathersa.co.za

By: Matt Silb

Matt Silb — Tue, 23 Jun 2009 04:59:02 +0000

Weather reports are for the general public. It is very uncommon to see confidence intervals presented in any reports to the general public.

By: Bob

Bob — Tue, 23 Jun 2009 04:41:54 +0000

Humans are too stupid and worthless to grab confidence indexes. The proof is how many females (emphasis on mothers) with say “theeey say that if you don’t eat your greens…”. The common issue is that many females, unlike males, dont look for the truth, females can be regularly caught looking for facts that support their agenda. Every read women’s magazines? Try it. You will be amazed at what they claim the whole US thinks based on a survey of 100 (sometimes up to 900) people. Little problem, there are 400 million people in the US. No matter, when an emotional female is flailing about because the world is catering to her agenda she will whip out all these things that “they” say. Next time our in this situation, ask to see the source document on look for the standard deviation (The probability the people doing the survey is wrong). If there is no list of what the error is, its probably so far off from reality, they didnt want to put that fact in there. To the point this is EXACTLY why weather forecasters dont put an error reading in their forecasts. If you could actually make sense of it, you would realize they get paid $150,000 a year to work for 15 minutes and be completely wrong.

By: Jerry

Jerry — Tue, 23 Jun 2009 02:51:53 +0000

I also wish they would add a variance for average temperature. Seems like we never get the average temperature — maybe it’s 60 on June 1 one year, 80 the next, and so the average is a normal-sounding 70. Yet it’s never 70 degrees on June 1.

Adding variance to the reporting could help make the weather forecast less ridiculous.

By: Tyrone

Tyrone — Tue, 23 Jun 2009 02:39:26 +0000

One fascinating weather theory is the Lezak Recurring Cycle.

By: kezerd

kezerd — Tue, 23 Jun 2009 02:00:23 +0000

here in the northeast part of Wisconsin, USA, you can be pretty confident any forecast for a period more than twelve hours in the future will be 100% wrong.

By: Ben

Ben — Tue, 23 Jun 2009 01:03:27 +0000

It does here bro http://www.eldersweather.com.au/