predicting the weather..

[BB_TX]

The way I have come to look at it is this. If they say 50% chance of rain, I assume 50% of the local area will get rain and 50% will not. Watching the radar that seems to generally be the case. He higher percentage stated, the more general the coverage of the rain is. The lower percentage, the more scattered it is.

 

[Bird]

[Statistically there's roughly a 50% chance the weatherman will be right.

We like to joke about it, and the weathermen are wrong much of the time if you are holding them to an exact temperature, but in reality, they're right, or very close most of the time. If they weren't, we all wouldn't be checking with them every day, would we?

 

[SkyPup]

Well, you could be a doctor or lawyer, charge big fees, give absolutely no guarantees, be wrong at least as often as the weatherman, and make even more money.

Or a politician, by definition -> any person skilled in manipulating group opinions in his or her favor....

 

[Amontilado]

Mike,

I'm down at the lower end of the state, near Mobile. Most of the time, I just sit back and see where the "discussion" goes.

Steve

 

[Amontilado]

Bird,
Exactly. Forecasting the weather is a case of what is an acceptable error. A couple of degrees off on temps for a nice, warm day isn't as much of a problem as being a couple of degrees off when the temps near freezing, and the difference can result in rain, freezing rain, snow or sleet or any combo of the above. Those days are the reason I keep a nice big bottle of aspirin here at work....

Steve

 

[johnk]

If you can't see the big storm approaching on the newest Radar screens and calculate the precipitation being dropped in its path you should have to admit your blindness on the weather channel for all to hear....Maybe stand on a snowbank in a T-Shirt and shorts for punishment for the next weathercast...

 

[thatguy]

thanks for all the comments and thoughts..

As a side story - A few years ago the local weather man (not meteorologist) said almost word for word on the 11 oclock news "the National weather service is calling for snow tonite, but I dont see where they are getting that information"...

Fast forward about 7 hours.. Notice how bright the bedroom is at 6am.. Open blinds and stare out at the 7 to 8 inches of new overnight snow.. He lost all of his credibility at that point for telling me what the weather was going to be ..

thanks

Brian

 

[Amontilado]

JohnK,
If it was only that simple. How about figuring how much precip will fall to the nearest 0.01" over an area encompassing several hundred square miles or more and in what form will it fall. Will the temps above the surface be warm enough for that falling snow to melt partially, completely, or not at all? What will the resultant ratio of liquid water to falling snow be (important to figure out how much measurable snow will be on the ground)? Our observing equipment has gotten better over the years, but with 200-500 miles between upper air stations (the places that release the balloons), plus the the fact that not as much info is returned from a radar as the tv people would let you believe (it can't tell if the precip falling is snow, rain, ice pellets, or even hitting the ground, though large hail is quite obvious if your looking for it, above the surface). A lot of what is happening between the RELIABLE observation points is assumed. We depend upon a lot of TRAINED HUMAN observers to help fill in the blanks, but they can't be everywhere, ans some of the public reports we get are less than credible (all wind damage MUST be because of tornadoes, right????).

As I remind some people, if you think you can do it better, give it a try. Trying to figure out the specifics of what a somtimes capricious person of the fairer sex (Mother Nature)is going to bring is that easy (have given up trying to figure out what's going on in my wife's mind ). It drives the wife nuts when I give a range of what could most likely happen in her little piece of space. Forecasting can be one of the most humbling professions I know, and from some of the stories I've heard, down right dangerous

Steve

 

[CRJCaptain]

I have a possibly stupid question. I want some help understanding weather predictions.

lets say we have a 30% chance of rain/snow - Does that mean it will rain/snow for 30% of the day or just we about 1/3 chance of rain/snow?

I am guessing the percentage has nothing to do with the length of the time it rains or snow.. Just the chance that it will rain/snow..

thanks

Brian

The percentage value has to do with the chance/probability that the precip in question will occur.

Keep in mind that these forecasts are generated by massive computer models that are solving the equations of motion for the entire atmosphere, run ahead in time several days. These equations are what are known in the biz as "non-linear partial differential equations". What does this mean? It means that any error or small deviation in the initial conditions will lead to a large divergence in the model's forecast solution. So in a way,there is a real limitation in how accurate and how far out in time any forecast will ever be. The inaccuracy is not the fault of the forecaster, but is more a function of trying to mathematically predict an inherently chaotic system.

Dean

 

[Amontilado]

CRJCaptain,
Basically correct.

The percentage value has to do with the chance/probability that the precip in question will occur.

Not quite. The chance of precip is the chance a MEASURABLE amount will fall.
A sprinkle or flurry doesn't count in the scheme, nor a light showers where only a TRACE amount (a non-measurable amount) occurs.

Keep in mind that these forecasts are generated by massive computer models that are solving the equations of motion for the entire atmosphere, run ahead in time several days. These equations are what are known in the biz as "non-linear partial differential equations". What does this mean? It means that any error or small deviation in the initial conditions will lead to a large divergence in the model's forecast solution. So in a way,there is a real limitation in how accurate and how far out in time any forecast will ever be. The inaccuracy is not the fault of the forecaster, but is more a function of trying to mathematically predict an inherently chaotic system.
*
Not quite again. The models, both in physical and statistical output is only guidance. We regularly depart when the guidance doesn't quite have things right. The guidance can only tell so much, with the rest being a lot of research and experience. True on the guidance likely deviating the farther out in time it goes. One of the tricks used is to run the same model equations with slightly different starting conditions. Take all the solutions, average them together, and one gets a better forecast, sort of like everyone chiming in on their best way to fix a problem, which I see so much (thankfully) on this site. Plus there is a LOT of sharing of meteorological data/guidance amongst countries (wish politics was this way ).

On a side note, for those in the deep freeze up north. The chile pepper folks in India have come up with a pepper even hotter than the red savina habenaro. Don't have the Chile Pepper Mag issue in front of me for the name, but this variety came in with a heat rating of near 1,000,000 units on the Scoville Scale. Probably a result of global warming, (or another cause ;-) ).

Steve