Construction weather days: baseline and monthly tracking
How many days the weather normally stops work at a site, month by month, from the nearest NOAA station and your contract's own rules, and how many it actually did since the project started.
Why a baseline matters
Most construction contracts allow time for a normal number of weather days and grant an extension only for the days above it. The claim rests on two numbers: how many days the weather usually stops work at the site in each month, and how many it actually did. Both should come from the same NOAA station with the same rule (for example rain of 0.10 in or more, a high below freezing, or wind above a limit).
What the tool does
- Takes your contract's rules (rain, snow, cold, heat, wind) in US or SI units.
- Finds the nearest NOAA GHCN-Daily station with a complete record and names it.
- Gives the mean and 80th-percentile weather days for each month over the last 10 years.
- Tracks actual weather days since the project start against that baseline, month by month, with partly covered months prorated.
- Emails the update on the 5th of each month for a saved project, and makes a PDF for the claim file.
Rain days a year in 30 US cities
Mean days with 0.10 in (2.5 mm) of rain or more, 2016–2025, NOAA GHCN-Daily, by month. Snow, cold and wind rules add days; run the tool with your contract's rules.
| City | Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Station |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Portland, OR | 98 | 14 | 11 | 12 | 9 | 6 | 4 | 1 | 1 | 4 | 9 | 13 | 13 | Portland Kgw-Tv |
| Nashville, TN | 84 | 6 | 8 | 9 | 7 | 8 | 7 | 8 | 7 | 5 | 5 | 5 | 8 | Nashville Intl Ap |
| Columbus, OH | 82 | 6 | 7 | 7 | 7 | 9 | 8 | 9 | 7 | 5 | 6 | 6 | 7 | John Glenn Intl Ap |
| Louisville, KY | 80 | 7 | 7 | 8 | 8 | 8 | 7 | 8 | 6 | 4 | 6 | 6 | 7 | Louisville Bowman Fld |
| New York, NY | 79 | 6 | 7 | 6 | 7 | 8 | 6 | 8 | 8 | 6 | 6 | 5 | 8 | Ny City Cntrl Park |
| Memphis, TN | 78 | 7 | 9 | 9 | 7 | 7 | 6 | 7 | 5 | 4 | 5 | 5 | 8 | Memphis Intl Ap |
| Detroit, MI | 78 | 6 | 6 | 7 | 8 | 8 | 6 | 7 | 7 | 5 | 7 | 6 | 6 | Windsor 4.0 Ne |
| Boston, MA | 76 | 6 | 6 | 6 | 8 | 7 | 6 | 7 | 6 | 6 | 6 | 6 | 6 | Boston |
| Charlotte, NC | 74 | 7 | 6 | 7 | 6 | 8 | 6 | 7 | 8 | 5 | 4 | 5 | 6 | Charlotte Douglas Ap |
| Indianapolis, IN | 74 | 6 | 5 | 8 | 8 | 9 | 7 | 8 | 5 | 4 | 5 | 5 | 6 | Indianapolis |
| Philadelphia, PA | 74 | 6 | 6 | 6 | 6 | 6 | 7 | 8 | 6 | 5 | 4 | 5 | 7 | Phila Intl Ap |
| Jacksonville, FL | 73 | 4 | 4 | 6 | 4 | 5 | 11 | 10 | 10 | 8 | 4 | 3 | 4 | Jacksonville Nas |
| Baltimore, MD | 73 | 6 | 7 | 6 | 6 | 8 | 6 | 8 | 7 | 6 | 4 | 4 | 6 | Baltimore-Washington Intl Ap |
| Washington, DC | 71 | 6 | 6 | 5 | 5 | 9 | 6 | 8 | 7 | 6 | 4 | 4 | 6 | Washington Reagan Natl Ap |
| Milwaukee, WI | 68 | 4 | 4 | 6 | 8 | 8 | 7 | 5 | 6 | 5 | 7 | 4 | 4 | Milwaukee Mitchell Ap |
| Seattle, WA | 68 | 10 | 8 | 8 | 6 | 3 | 3 | 0 | 1 | 3 | 6 | 10 | 10 | Seattle Boeing Fld |
| Chicago, IL | 67 | 3 | 4 | 7 | 7 | 8 | 6 | 7 | 6 | 5 | 7 | 4 | 4 | Chicago Midway Ap |
| Houston, TX | 67 | 6 | 4 | 4 | 4 | 6 | 8 | 7 | 6 | 6 | 5 | 5 | 5 | Houston-Westbury |
| Dallas, TX | 52 | 4 | 5 | 5 | 4 | 7 | 5 | 4 | 4 | 4 | 5 | 4 | 3 | Dallas Faa Ap |
| Oklahoma City, OK | 49 | 2 | 4 | 4 | 6 | 7 | 6 | 4 | 5 | 4 | 4 | 3 | 2 | Oklahoma Cy Will Rogers World |
| Austin, TX | 44 | 3 | 2 | 4 | 4 | 7 | 4 | 3 | 3 | 3 | 4 | 4 | 3 | Austin-Camp Mabry |
| San Francisco, CA | 41 | 8 | 7 | 8 | 3 | 1 | 0 | 0 | 0 | 0 | 2 | 4 | 8 | San Francisco Dwtn |
| San Antonio, TX | 37 | 2 | 2 | 3 | 4 | 5 | 4 | 3 | 3 | 4 | 3 | 3 | 3 | San Antonio Stinson Muni Ap |
| Denver, CO | 33 | 2 | 2 | 3 | 4 | 6 | 4 | 3 | 3 | 2 | 2 | 2 | 1 | Denver Water Dept |
| Los Angeles, CA | 20 | 4 | 3 | 4 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 2 | 4 | Los Angeles Downtown/Usc |
| Albuquerque, NM | 20 | 1 | 1 | 1 | 1 | 1 | 2 | 4 | 2 | 2 | 2 | 2 | 1 | Albuquerque Intl Ap |
| El Paso, TX | 18 | 1 | 1 | 1 | 0 | 0 | 2 | 3 | 4 | 2 | 2 | 1 | 1 | El Paso Intl Ap |
| San Diego, CA | 15 | 4 | 2 | 4 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 3 | N Is Nas |
| Phoenix, AZ | 15 | 2 | 2 | 2 | 0 | 0 | 0 | 2 | 2 | 1 | 1 | 1 | 2 | Phoenix Ap |
| Las Vegas, NV | 8 | 2 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | Las Vegas Air Terminal |
From schedule to building performance
EPW.tools also makes hourly EnergyPlus weather files (EPW) and design conditions for the building itself, from the same station networks: design conditions, Manual J design temperatures and future-climate files.
Frequently asked questions
What counts as a weather day?
Whatever the contract says. Common rules are rain of 0.10 in or more, snow on the ground, a high below freezing or wind above a limit. The tool takes any combination of rain, snow, cold, heat and wind thresholds.
Which weather station is used?
The nearest NOAA GHCN-Daily station within 30 km with precipitation reported on at least 90 % of the days, preferring National Weather Service stations. The report names it, as most contracts require.
What is the 80th percentile?
The number of weather days exceeded in one year in five for that month: a more conservative allowance than the mean.
Can it track a project month by month?
Yes. Save a project with its start date and rules, and an email on the 5th of each month gives the actual weather days against the baseline and the running excess.
Is this legal advice?
No. The report records the data and the method; how days are counted is set by the contract.
Check a site
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