Background: I am managing a Project where I am responsible planning the construction of a visitor center on the peak of a mountain.

The Problem: During reading the brief, I have came across the following statement: "Poor weather conditions often make the peak inaccessible from November to March each year."

The Question: How would I adjust for the period between November to March? The statement above states "often," which I believe implies that some days between November to March will be accessible. However, how would I go about this? Do I simply assume the number of days which will be available for work by calculating number of days from November to March and finding the average?



This is no different than the probabilistic of weather events and those projects that can be affected by weather. And it is even similar to the probabilistic availability and performance of labor and machine resources. The key is to understand the distribution of weather impact on the mountain over many years. This means, in order to properly plan work on the mountain, you need to find credible, historical data on weather patterns over the mountain; plot the distribution of those events, and then choose the planning value that represents the degree of risk you are willing to assume.

Using mean average can be very flawed depending on the skew of that distribution. So it is important to understand the distribution.

You cannot mitigate weather; you can only plan for resilience to the degree possible. That might only mean a decent amount of cash in reserves in order to fund weather delays that are out of everyone's control. It could mean doing other work at another location when access to the mountain is closed.

  • First of all, thank you for your answer. Secondly, what if I have been given no historical data? The only information provided to me is the fact that it may be inaccessible from November to March. Though I guess I can complete other work whilst access to the mountain is closed. Thank you for your help. Nov 30 '14 at 20:41
  • 2
    Not sure where you are in the world but around where I am weather data are reasonably obtainable through a bit of research. The research would be a required part of your estimating process because, without, your estimates and planning values are not credible. If you are simply unable to get the information, I guess you have no choice but to make a risk averse assumption and slap something like 20% availability. With a lack of information, you can use a bit of inductive reasoning but your planning values would be a significant risk. Nov 30 '14 at 20:46

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