WRAL WeatherCenter Blog

Fishel: Expressing uncertainty in weather forecasts is not being wishy-washy

Posted March 7

Since it is impossible to generate a "perfect" analysis of the current atmospheric state, no computer forecast has a prayer of producing a perfect forecast.

Undoubtedly, many of you are familiar with the chaos theory. Dr. Edward Lorenz published a paper in 1963 in the Journal of Atmospheric Sciences in which he spoke of the chaos theory. As it relates to weather prediction, his point was that in numerical weather prediction, the atmosphere is very sensitive to initial conditions, and that imperceptible differences could lead to large differences in the forecast.

Since it is impossible to generate a "perfect" analysis of the current atmospheric state, no computer forecast has a prayer of producing a perfect forecast. Until recently, meteorologists were restricted to using what we call deterministic forecasts. In other words, a given model was saying to us "here's my solution-take it or leave it!".

Well, with few if any alternatives, we almost had to follow it, although experience and the school of hard knocks would help many forecasters to learn the biases of a given model, and to try to account for them.

Now, with more computing power than at any time in the history of mankind, we can generate what we call ensemble forecasts. One technique used widely is to "perturb" or alter the initial conditions of the model just slightly to 20, 30, or even 50 different extents. By doing this, in a sense, we are accounting for those errors in the analysis, with the goal being to see how sensitive the atmosphere is to these changes in the starting point of the model forecast.

Ensembles allow meteorologists to assess the degree of sensitivity of the model forecast to these small changes, and to quantify the amount of uncertainty in the solution by looking at the variance in the forecasts. This is 21st century technology at its finest!

Now, I can certainly understand how this "new" verbiage could be misinterpreted as "copping out", or taking the "CYA" approach to forecasting. You might have even had this thought: "Gosh, when I was younger, these TV guys and gals used to take a stand and commit to a forecast. Even if they were wrong, I respected them for committing to a forecast".

Well, guess what? We didn't know what we didn't know! Now we have a much better idea as to how, why, and where things could go very wrong. When my colleague Nate Johnson and I took to the road late in the evening on Jan. 6, we experienced rain at the WRAL studios, slushy roads at the Harrison Avenue exit off Interstate 40, and all snow at the Davis Drive exit of I-40.

Those are big differences over a very small distance. Would you rather I, or any meteorologist, "guess" where that transition zone will be, or be honest with you and inform you of the large variety of conditions possible where you live? I would hope the latter.

When a meteorologist tells you they don't know, or they're not sure, it's not that they haven't done their homework, or that they're just not willing to commit. It does mean that they're being honest and forthright with you when they talk of uncertainty. If you hear "Duh, I don't know", that's not good. But if you hear an honest appraisal of a challenging forecast scenario, and the sharing of the 2 or 3 most likely scenarios, you are the recipient of a forecast based on the most advanced science available to the meteorological community.

Our challenge is to continue to strive for better ways to communicate that level of uncertainty, not just on television, but on all the platforms where weather forecasts are disseminated. Apps on your phone, by their very nature, do not provide much context-you see an icon and a number for each day. That has to change, and WRAL, along with TV stations all across the country, are trying to figure out how to do just that. In the meantime, if you have any ideas as to how that forecast certainty or uncertainty can be better communicated, by all means let us know.


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  • Fred Neopolitano Mar 11, 2017
    user avatar

    As Greg said on the air after the Jan. 6 incident, people just need to "get over it." Weather forecasting is an imperfect science. Just be glad Greg and the team are there to warn us of severe weather.

  • Franklin Nanney Mar 10, 2017
    user avatar

    I don't read this article as being defensive. Just explaining how technology is changing the way weather is forecasted, especially to the many "armchair meteorologists" as someone said below.

  • Janice Daugherty Mar 9, 2017
    user avatar

    Stay calm. It's the weather. You report it, you don't control it. No need to be defensive. Easy now.

  • Jeff Franklin Mar 9, 2017
    user avatar

    The problem seems to be simple. For most folks, the advent of more "computing" power have made things more precise. You can get definitive answers quickly, a bank balance, your stock portfolio, any number of things.

    The same does not apply to weather. The increase in computing power has not made predicting it any more precise, but has allowed for more variables to be entered and analyzed, which provides more options and more forecast possibilities.

    In the end, it is still the weather, which is always going to have an element of unpredictability. Pretty sure the Greg and the team are doing all they can do to minimize that, but they are still sometimes at the mercy of things beyond their control.

  • Roy Pine Mar 8, 2017
    user avatar

    View quoted thread

    Given the usual crowd of yahoos and armchair meteorologists that love to chime in when a snow forecast fizzles, I'd say yeah...He apparently *does* need to explain it to people.

  • Andy Holt Mar 8, 2017
    user avatar

    Is it obvious to anyone else that Greg has become a little offended, and just a bit abrasive when explaining the obvious to us mere mortals. It is VERY obvious that anyone knows that the weather can change in a hurry, and you may have rain falling outside of your window, and you go down the road 2 blocks and the pavement is dry. Apparently someone must have commented at some point that he was "wishy-washy", and he feels the need to explain? Calm down Greg, you are still doing a commendable job... we don't expect you to be 100%?

  • Russ Bullock Mar 8, 2017
    user avatar

    Excellent explanation Greg. Now let's just hope the National Weather Service budget is not cut to the point that we have to go back to using only the one model simulation.