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Source: https://outdoors.stackexchange.com/q/1536
License name: CC BY-SA 3.0
License URL: https://creativecommons.org/licenses/by-sa/3.0/

<p>All outdoors activities precautions include taking note of the weather forecasts for the day.</p>

<p>However, I have seen those forecasts be terribly wrong in many places, even for a two-hours ahead prediction.</p>

<p>So, what are the conditions that make weather forecasts reliable? Up to what duration?</p>

<p><hr></p>

<p><em>Example:</em></p>

<p>In the French riviera, near the Alps (Nice backcountry), where both the sea and high (~1200m) mountains are within 10 km, the weather forecasts are totally unreliable, from one day on the next one, but even from 8 AM (storms announced, rain visible) to 11 AM (storms announced, bright sun visible).</p>

<p>Inversely, in central France (Burgundy), in a much more continental weather,  predictions are reliable up to 2 days ahead with good confidence, both for temperatures and rain. 1 hour-ahead to-the-minute rain predictions are correct 90% of the time.</p>

<p>Based on that limited experience, I would tend to say that sea and mountains are reasons for unreliability. But up to which distance? What about oceans? From which heights to mountains impact? Are certain seasons more error-prone than others? etc etc</p>