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How reliable is a 15-day forecast?

Ok, so I live in Texas and have had about enough warm weather and am just curious how seriously I should take a 15-day forecast, like on I am just a little wary because I remember the week before Thanksgiving I was looking at various weather sites and they all said the high would be like 75 in Austin/Dallas and turns out come Thanksgiving, the high was 45 and the low was 30! I would say they were more than a little off. So, am I right to be skeptical?

9 Answers

  • Water
    Lv 7
    1 decade ago
    Favorite Answer

    I will try to keep this short but it is a very difficult question to answer.

    I have forecasted for over 35 years and have seen the forecast expanded from 48 hours to the 7 day period that is most common right now.

    When the forecast was expanded to 5 days in the 1980s, I was very skeptical as to how well it would be received since the verification showed that skill beyond 3 days at the time was very small and there would be large changes as the extended period advanced into the range where skill scores were fairly good. But, the forecasts were welcomed with great acceptance for people who plan things far in advance.

    When the forecasts were expanded to the current 7 day period in the 1990s, I again was very skeptical for the same reason. Verification scores show improvement in the days 5 through 7 but they are not the greatest and often show big errors especially in the "cool" season (winter).

    In my opinion, the private forecasting firms that advertise a 15 day forecast are trying to imply that their forecasters are better than others just because they forecast for a longer period. I doubt that they are too concerned with accuracy. They are using it more as a marketing ploy to get people to pay for their services.

    I will say, that on occasion, there is a storm system that can be picked out of model data over a week in advance. The winter storm that moved across the Northern states this past weekend was an example that showed up very early in the forecast cycle. However, the details such as the track and intensity at that time period are hard to come by. About the best that can be said is that it can be used as a tend forecast that may give an indication that it is warmer or cooler than ususal or that precipitation is more or less likely. At this point any detail is, at best, a long shot.

    Source(s): an old forecaster
  • Anonymous
    5 years ago

    Nope. There's a mathematical limit to how accurate you can make a weather forecast. 15 days in the future is far beyond the realm of certainty because weather systems have a lot to do with these things called Lorentz attractors. The sunniness of California 15 days in the future may not depend on whether a butterfly is flapping it's wings in Japan, but it may very well be influenced by how much methane the dairy farms of Hawaii produce and exactly when a single thermal lifts off from the ground. There is a fairly good chance that the forecast will change. How good a chance? About 40% or better.

  • 1 decade ago

    The reliability of a weather forecast decreases with time. You can see that on maps of the probable evolution of a hurricane, it is a cone of probability. After 15 days, the probability for the weather to happen can be e.g. 15%. The question then is; are you willing to plan e.g. a barbecue with only 15% chances that the weather will be clement?

    In aviation, the weather forecast for an airfield that is called TAF gives you forecast for 9 and 18 hours. Even so, if uncertain, the message will e.g. give PROB30 TS, which means: a 30% chance that thunderstorm will develop.

    On the other side, a paradoxal thing is that, the longer a high pressure holds, the more stable it is and the longer it will last. When that happens, weather forecasting is an easy task. But SIGMET (signifiant meteorological phenomenons) like thunderstorm or fog can be difficult to forecast for certain.

  • Anonymous
    4 years ago

    15 Day Forecast Dallas

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  • 1 decade ago

    winds shift,,, and other variables... can change the weather in a heartbeat. nothing is etched in stone. systems..coming slowly your way.... speed up... clouds dry out. a seven day forecast is tough... but more reliable.. than the additional days. i prepared for a major storm in the summer... and the day before it shifted to the southeast.. and voila... a gorgeous day. glad i did not cancel my plans.

  • Will
    Lv 5
    1 decade ago

    yes, a 15 day forecast is not very reliable.

  • canam
    Lv 7
    1 decade ago

    Its reliable the day it is posted. Thereafter, conditions can change and that changes the forecast.

  • shufly
    Lv 4
    1 decade ago


  • 1 decade ago

    As reliable as you,jok'in,50%

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