What information does a weather forecast contain?

A colleague of mine said something years ago that struck me as insightful:  every model forecast ever issued was wrong!  Wrong in some way or another, to a greater or lesser extent.  Obviously, some forecasts are better than others, but none of them have ever been absolutely perfect.  His point was to suggest that human forecasters need to avoid basing their forecasts purely on Numerical Weather Prediction (NWP) model output - a notion with which I agree fully.  However, the same can be said of every forecast ever issued by human forecasters, as well!  The reality is that we can never predict the weather with absolute certainty.  I've not the space nor the inclination to go into the details of why this isn't just my opinion (maybe later) - it is, rather, based solidly in our scientific understanding of the atmosphere.  So, put in terms of the information content of a weather forecast of any sort, a weather forecast is not a statement of what definitely and certainly is about to happen in the future, in detail.

Because weather has substantial impact on human society, it's obvious that people want to know what's going to happen weatherwise ahead of time.  I'm fond of saying "Yes, of course, and people in Hell want a glass of ice water!" - which I heard many years ago from a co-worker.  What people want isn't necessarily what they're going to get.  The fact is that we have never been able to provide that sort of information and there is every reason to believe we'll never have that capability.  That notwithstanding, our relationship to our users predominantly has been such as to perpetuate the myth that we can provide that with 100% confidence.  Users want something and we pretend we can give it to them.  Surely our users know by now that such a capability doesn't exist!  Their own empirical evidence is that we can't do it and that evidence is at least a contributor to the widespread notion that weather forecasts are inevitably and totally wrong.

If plausible bounds are put on what constitutes a good forecast (as opposed to a perfect forecast), it should be noted that these days, today's weather forecasts are correct (within those bounds) a high percentage of the time (e.g., for 24-h daily maximum and minimum temperatures within 5 degrees of the observed value, it's about 85% or better).  So our weather forecasts currently contain useful information (despite not being perfect), within some limits, out to about 7-10 days.  What you experience is usually fairly close to what we forecast most of the time.  Beyond that "predictability limit" of 7-10 days, our weather forecasts become no more accurate than what we would see if we simply forecast what climatology (i.e., the long term averages for a particular location, date, and time) says we should expect.  At that limit point, we say our forecasts no longer have any skill, relative to climatology.  The greater the lead time, the less accurate the forecasts (and the lower their skill), on the average, out to the predictability limit.

What I would like to have us do is re-negotiate the contract we have with the users of weather information.  We need to be able to provide them with whatever forecast information we have, including some sort of statement of the uncertainty associated with the information we have.  Let's put aside the existing relationship, in favor of putting information out that we actually have to capability to provide!  Now the language of uncertainty is probability, and I'm constantly being told that people don't want probability (the glass of water in Hell problem) or they don't understand probability.  You don't need to be an expert in probability theory to put it to good use, and many people are very familiar with the notion of odds (probability in another form).  What we are doing now, with the lone exception of precipitation probabilities, is pretending to provide absolute certainty.  The historical background of how Probability of Precipitation (PoP) was introduced is interesting but far more than I want to expound upon in this blog.  Whatever the problems are with PoPs, they are a far more meaningful way to express our forecast information than all the non-probabilistic elements in a weather forecast.  If we don't express our uncertainties, we are actually withholding information from forecast users!  That can't be a good thing, and it comes back to bite us, time and time again.

An analogy with sports is a fair comparison, at least to some extent.  Our predictions for who will win the Super Bowl in the pre-season have much greater uncertainty than the night before the game is actually played.  Even then, there remains some uncertainty, and reasonable people can disagree about the outcome right up to the time the whistle blows and the winner is known with absolute certainty.

Therefore, to answer the question posed by the title of this blog, a weather forecast contains the forecaster's best estimate of what that forecaster (who might possibly be an NWP model) anticipates is going to happen with the weather.  It's not a guess, but rather our assessment of the situation and what we believe is the most probable weather that will occur, at the time we issued the forecast, given the finite accuracy limits on the method used to create that forecast.  As new information comes in, that forecast can change, sometimes dramatically.  Our diagnosis of what is about to happen virtually never coincides precisely with reality, but at times we can get it fairly close, especially at the shorter lead times.

A weather forecast always should include information about forecast uncertainty and that is necessarily going to be more complicated to explain than just reading a list of numbers.  More information inevitably requires more effort.  If the user is going to make the best use of the information we reasonably can provide, the user must accept some of the responsibility to pay attention to the forecast, to learn what the forecast actually is saying.  If all you want is the numbers, then you've forfeited a good deal of the value the forecast is trying to provide.  The choice can be left up to the user.

Forecast frustrations

Yesterday's events in the southeastern US have revealed, yet another time, how frustrating it can be to be a forecaster.  Forecasting the weather well is not easy, and there is always the inevitable uncertainty in our forecasts.  Most of the angst forecasters feel when doing their job is derived directly from that uncertainty, and yet that very aspect of forecasting is inescapable.  Although not all forecasters are thoroughly committed to their work, most of those I know are indeed very much absorbed in trying to do their absolute best, all the time.  Forecasting is the most challenging task a meteorologist can tackle and anyone who thinks otherwise is welcome to have a go and see how it works out!

Therefore, it's extremely frustrating when forecasters provide good forecasts and people are still caught in bad weather situations, occasionally becoming casualties of that weather.  In 1987, the Midland, TX forecast office did a superb job with a tornado warning, but the small town of Saragosa was blasted by a violent tornado.  About 10 percent of the town population was killed, including several children!  The forecaster who issued the warning knew some of those killed, and he was devastated by what happened.  It was no consolation to him that he had done his part and done it well.  I was deeply moved by seeing his emotional state - years later, he was still racking his brain trying to think of what else he could have done to prevent the tragedy.  Most forecasters care very much about their job performance, because they know they can make a difference.

What does it take for a forecast to be effective?  Assume that the forecast is perfect (which is impossible).  Then, for that forecast to be effective, the users of that forecast must

1. receive the forecast information
2. understand the forecast information
3. know what to do with the information
4. believe the information
5. be able to take effective action based on that information
6. make the decision to take action when necessary

Every link in this chain is important for the final result.

The winter storm that hit the southeast yesterday affected people who aren't accustomed to such events.  Some were hit very hard with the weather, despite good forecasts well in advance.  Since I've been a professional meteorologist, it's always been frustrating to me that people who experience hazardous weather events that are relatively rare in their region often do little or nothing to prepare for them.  This is no laughing matter - the consequences can be dire.  If such weather events only occur once every 20 years or so, it seems easier and cheaper to do nothing to address their preparedness.  And many people ignore the forecasts, seeking to go about their ordinary business despite the extraordinary weather conditions.  It's as if they want things to be normal and somehow believe they can force the situation to be normal by behaving normally - in abnormal circumstances.  Users surely must believe the forecasts if they are to help themselves make the right decisions.  Was a lack of belief in the forecasts why so many were caught in life-threatening situations by yesterday's winter storm?  It might be helpful to do a serious survey to investigate the reasons.

If a particular form of hazardous weather is rare in your location, that doesn't mean it can never happen - only that it will be infrequent.  And yes, it can happen to you, in particular!  It's not just about hype and scare tactics - hazardous weather is serious business - definitely not a joke.  Sure, sometimes it turns out to be a false alarm, and forecasters try very hard not to have that happen - but uncertainty means it happens occasionally.  That doesn't mean you can dismiss the forecasts as hyperbole all the time!

It's always better to have something you might need in a hazardous weather event and it turn out that you didn't actually need it, than for you to need it desperately and not have it.  If you expect the best in a situation (e.g., "A tornado won't actually hit my house!"), nevertheless, it's prudent to prepare for the worst, right?  After all, your life and well-being, and those of your loved ones are potentially at stake.  That seems so obvious to me, it's just difficult to imagine why many people behave in ways potentially detrimental to their own self-interest.

I can't pretend to understand why some people refuse to recognize the value and importance of weather forecast.  Yes, the forecasts aren't perfect, but many times, those forecasts offer critically important information for the decision-making process.  A friend of mine told me years ago that "Where you stand on some issue depends on where you sit!"  From where I sit, it's silly and dangerous to ignore the information in a forecast of hazardous weather.  But evidently, from where some people sit, it's quite all right.

It's the job of the forecaster to make as accurate a forecast as possible, but forecasters have little or no control over what must happen to make that forecast effective!  Their primary responsibility is the production of an accurate forecast.  That's what they're educated and trained to do.  Forecasters are basically helpless when any link in the chain breaks - preventing those links from being broken isn't what they're educated and trained for.  It's likely that efforts to educate users about how to understand and use the information would be helpful.  Even if a serious public education campaign were to be done, it likely wouldn't be a perfect solution.
There are many agencies that offer information that can be life-saving regarding hazardous weather, including the National Weather Service, but users must accept the responsibility for their own safety - to learn and put into action the available recommendations.  We can lead the horses to water, but it's up to them to drink.
 

The indifferent stars - More musings about the meaning of life

A friend just posted on Facebook about how stars had to die for us to exist at all.  This stimulated a question in me:  should we worship stars because they died so we can exist?  After all, at least one popular religion worships a deity-figure who supposedly died on their behalf.  A modern physical understanding is that all the atoms that give us existence were cooked up in stars and released by supernovae.  Star stuff come to life, as the late Carl Sagan described us, contemplating our place in the universe.  Apart from notions that what we call 'reality' is simply an illusion, there can be no argument that stars are real.  There's abundant evidence that the core of scientific understanding about stars is in fact a valid interpretation of our star observations.  Those born in the 20th century and after are the first humans to have any understanding of what the stars actually are and how they work.  Our sun is a star, of course, and given that there have been sun-worshippers, why not star-worshippers?

But if stars aren't conscious beings, so far as we can tell, then how could they serve as deities for us, even as they surely are in a very real sense our creators?  We surely were not the product of a conscious intent of stars.  The stars are simply matter and energy, going about their star 'lives' following the laws of physics.  As they are born, mature, and decay, matter and energy flow through them, the atoms now constituting a star aren't the same atoms that made up that star when it was born.

Allow me a diversion into personal experience.  Many years ago, I had a revelation about thunderstorms.  Thunderstorms are not objects, in the sense that they represent a fixed collection of atoms and energy.  Rather, they are processes.   Atoms and energy flow through that process, producing the observations we can make.  Ignoring all the microscale events (quantum fluctuations, etc.), an object  (or, thing) is predominately made up of the same matter from one moment to the next.  A wooden stick, or the water in a sealed container are examples of "things".  If we burn that stick or allow the water in a container free access to its surroundings, there will be changes to the matter and energy distributions.  The stick or the water will be transformed and subject to various processes by which the atoms and energy will be re-arranged, re-combined, and re-distributed.  The stick or water will no longer be in its original form, but the sum of its energy and matter will still exist (remember E = mc² and the conservation of energy?).  A thunderstorm is a process and there's no clear boundary separating that storm from its environment - how does one draw a bag around a process by which atoms and energy flow through a process?  Where does that process begin and the environment end?

Curiously, we humans can be thought of in very similar terms; i.e., as processes.  The atoms and energy enabling everything we are and everything we can do change with time.  We're not made up of the same atoms and energy that made us up the day we were born, or even conceived.  Although we often think of ourselves as fixed entities, but our consciousness deceives us - it's part of a process that continues throughout our lives within us.  That process includes memories of earlier existence, obviously.  Only lately have we begun to plumb the depths of the connection between our consciousness and the matter that constitutes the framework of our consciousness, a lattice upon which our thoughts are operating.  We have much to learn about that but we do know that our consciousness doesn't survive the death of our bodies.  The existence of something else - call it a soul - that is claimed by some to live beyond our physical existence is unobserved and evidently unobservable, as well as unlikely.

Although stars have matter and energy flowing through them, like we do, I have no way of knowing whether or not stars have consciousness and can think of themselves as entities.  I rather doubt it.  In any case, our physical existence (and the existence of all living entities) is very similar to the existence of the nonliving part of the universe including the stars:  processes going about their business, necessarily obedient to the laws of the natural universe.  One could easily go from this vision of the universe to a sort of pantheism:  We are one with the universe, not man apart from it - a feeling that many have shared as they stared at the stars in the night sky.  Star worship would not be a completely absurd point of view, as the deaths of stars mark the beginnings of our creation in a real way, somewhat analogous to conception.  Science has  connected us inadvertently to something profound (as it often does):  we and the universe are one at a deep level.

The thing about the stars is that no one has a basis to argue that the stars had conscious intent for parts of their matter and energy to be transformed into human beings.  The stars, like all the rest of natural world insofar as we can tell, are absolutely indifferent about our existence.  The stars existed long before us, and will exist long after the human race is gone.  We could worship stars, but the stars can't reciprocate or benefit in any way from our worship.  Our lives have no meaning to the stars, any more than the lives of most particular stars have no meaning to us.  If a nearby star goes supernova and the Earth is bathed in deadly radiation, it will not be the stars punishing us for our transgressions.  Stars are neither good nor evil - but their existence was necessary for us to contemplate ourselves in the context of the universe.

Stars are far closer to us in spirit than some collection of late Bronze Age/early Iron Age mythology, for which zero tangible, credible evidence exists.  If someone feels they must worship something large and powerful, stars make more sense to me than the imaginings of ignorant barely-civilized people thousands of years ago.  If we're inclined to see a meaning for our existence, it's not at all obvious that if you reject Abrahamic religious mythology, there is any meaning to it whatsoever, outside of any meaning you might make up for yourself.  I'm fine with that.  What about you?