Construction Weather Delay Impact Calculator
Based on 30-year NOAA normals for Texas, 36 adverse weather days are anticipated over the 183-day project duration.
Monthly Breakdown
| Month | Days | Precip | Freeze | Wind | Total Adverse |
|---|---|---|---|---|---|
| April 2024 | 30 | 6 | 0 | 0 | 6 |
| May 2024 | 31 | 7 | 0 | 0 | 7 |
| June 2024 | 30 | 7 | 0 | 0 | 7 |
| July 2024 | 31 | 5 | 0 | 0 | 5 |
| August 2024 | 31 | 5 | 0 | 0 | 5 |
| September 2024 | 30 | 6 | 0 | 0 | 6 |
This weather delay calculator estimates how many adverse weather days a construction project should anticipate over its schedule, following the U.S. Army Corps of Engineers (USACE) approach of comparing actual weather to historically normal weather. It uses bundled 30-year NOAA climate normals for each state to count expected precipitation, freezing, and high-wind days month by month across your project window, and can compare anticipated days against the actual adverse days you experienced to estimate excusable delay.
Formula
Anticipated adverse days = Σ over months min(precipDays + freezeDays + windDays, overlapDays)
- precipDays
- Normal precipitation days for the month, scaled by the fraction within the schedule
- freezeDays
- Estimated days below the temperature threshold when the average low is colder
- windDays
- Estimated high-wind days when average max wind nears or exceeds the threshold
- overlapDays
- Days of the month that fall within the project window (the monthly cap)
How it works
- Select the project state and enter the start and end dates. Set the thresholds that make a day adverse: precipitation (default 0.1 in/day), minimum temperature (default 32°F), and wind speed (default 35 mph).
- For each month overlapping the schedule, the calculator scales the state's normal precipitation days by the fraction of the month covered, estimates freeze days when the average low is below the temperature threshold, and adds high-wind days when average max wind nears or exceeds the wind threshold.
- It sums anticipated adverse days (capped at the calendar duration) and, if you enter actual adverse days, splits them into excusable delay (actual beyond anticipated) and non-excusable days, with a USACE-style summary.
Worked example
A Texas project running January 1 to March 31 with default thresholds (0.1 in precipitation, 32°F, 35 mph wind).
- January (31 days): normal precipitation ≈ 6 days; average low 37°F is above 32°F so 0 freeze days; max wind 13 mph is below threshold so 0 wind days → 6 adverse days.
- February (28 days): ≈ 6 precipitation days, 0 freeze, 0 wind → 6 adverse days.
- March (31 days): ≈ 7 precipitation days, 0 freeze, 0 wind → 7 adverse days.
- Total anticipated adverse days: 6 + 6 + 7 = 19 over 90 calendar days.
About 19 anticipated adverse weather days over the 90-day Texas winter schedule, driven entirely by precipitation since temperatures stay above freezing and winds stay below the threshold.
Frequently asked questions
- What is the USACE weather delay methodology?
- The U.S. Army Corps of Engineers approach sets an expected number of adverse weather days for each calendar month based on historical climate data. Only the actual adverse days that exceed that anticipated baseline are treated as excusable delay warranting a time extension.
- What counts as an adverse weather day here?
- A day is adverse when measurable precipitation exceeds the precipitation threshold, the temperature falls below the minimum temperature threshold, or wind speed reaches the wind threshold. You can adjust all three thresholds to match the weather sensitivity of your specific work activities.
- How is excusable delay calculated?
- Excusable delay is the amount by which your entered actual adverse days exceed the anticipated baseline for the schedule. Days within the anticipated count are considered normal weather the contractor is expected to plan around, so they are non-excusable.
- Are the climate figures exact for my jobsite?
- No. The tool uses representative state-level 30-year normals, so it gives a planning estimate rather than site-specific weather. For a formal time-extension claim, support it with actual NOAA station data for the project location and your daily field weather logs.