Weather Delay Days by Metro

How many workdays a construction site actually loses to weather, metro by metro — from ten-year NOAA station baselines, scored against each location’s soil rather than rainfall totals alone.

Why rainfall totals mislead

An inch of rain costs a sand site nothing and a clay site three days. The column that matters below is not rainfall — it is lost workdays, which is rainfall put through a soil-specific drying model. Metros are ranked worst first.

Metro	Soil	Worst month	Lost workdays that month	Rainfall / yr
Atlanta, GA	Clay	January	16	56.1″
Boston, MA	Silt	January	16	43.4″
Richmond, VA	Clay	January	15	49.1″
Phoenix, AZ	Sand	February	2	8.6″

Atlanta, GA currently tops the list: 16 unworkable workdays in January. Rainfall alone would not have told you that — several wetter metros lose fewer days because the water drains.

Note how often the worst month is a winter one rather than the wettest. Frontal rain arrives spread out and each event collects its own drying tail; summer storms cluster, and their tails overlap. The same rainfall costs more when it is spaced out, which is why totals mislead.

How to read these

Each metro page carries the full monthly table: the ten-year mean (the number to carry in a bid), the median, and an abnormality threshold set at the mean plus one standard deviation. Exceeding a mean is the expected case in roughly half of all periods and is not by itself evidence of abnormal weather; the threshold is the stronger basis for a claim.

These are monthly figures and should not be summed into a year. Each month assumes a site in the condition it is in that month. Adding twelve together would assume a jobsite never improves — no stone haul roads, no stabilised pads, no ditching — which is wrong for any project past its first few months. Over the two-to-four week window a delay claim actually covers, the effect is negligible. Over a year it is not, so we do not publish an annual figure.

Every page names the NOAA station it used and its distance, the soil basis and the effective drying constant, so the figures can be checked rather than taken on trust.

Baselines rebuilt August 1, 2026. Figures model soil-dependent site work — earthwork, grading, excavation, foundations and underground utilities. Enclosed and vertical work is not modelled. Planning figures from station observations and a deterministic soil model, not site-specific geotechnical findings.