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Adverse weather impacts our work expectations. Normal adverse weather refers to the extent of the weather work delays that one would expect after looking at past weather data. In the previous blog, Benefits of Using Weather Data When Project Planning, we identified the factors to consider when converting weather conditions into weather delays. Now, we’ll look at the technical and practical aspects of planning for weather, and how NetPoint makes it easier than ever to plan for weather delays in a nuanced and intuitive way.

NOAA and NWS both have stations around the country that publish data you can use to get detailed information about the weather near your building site for the last 3-10 years. You can use this to find, say, the average number of days that rain falls in March in Seattle, or the average number of days that the temperature is over 80°F in August in New York.

Below: NetPoint’s weather module, which draws on NOAA data.

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So, let’s say you want to know how much adverse weather to expect in Orlando. The key issue is probably going to be rain; rain is going to impact construction work no matter what the activities are. You can run a weather report in NetPoint: using NOAA data, NetPoint will calculate the average number of day’s rain fell in each month over the last ten years and report it like this:

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For each month, you can enter the expected number of adverse weather days into a calendar. A calendar in NetPoint specifies which days are working days and which days are not. The default calendar in NetPoint takes national holidays and weekends into account and can be edited under “Tools” “Manage Calendars”.

The calendar knows that the NOAA data is drawn from the full month, not just working days, and so applies conversion factors before calculating the impact on the schedule (for example, seven rain days overall becomes five rain days on work days; measurements from a 24-hour day are adjusted for the duration of the relevant workday).

The quantity of precipitation determines its effect on work.  As noted in the PMA publication, Force Majeure Weather Modeling, rainfall <.1” is a drag on productivity; >.1”, causes an interruption of work. Looking at the screenshot below, you’ll see you can adjust these values in NetPoint’s weather module, as well as set the length of a workday:

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Obviously, this is only good for an estimate – actual adverse weather could turn out to be very different than the previous ten years! But this is as dependable as a method can be.

The only remaining question is: how to incorporate weather days into your plan? Do you extend the length of the activities? Do you add weather-specific activities to create float that represents uncertainty?