Anticipated adverse weather: building a baseline your contract will actually accept
Weather time extensions turn on a comparison against what was reasonably anticipated. How to build that baseline from NOAA data, per-activity thresholds, and the controlling path — before you need it.
A superintendent can tell you exactly which days were lost to weather. The daily reports say rain. The photographs say mud. Everybody on the job agrees. And the time extension still gets denied, because none of that answers the question the contract actually asks.
The question is not whether the weather was bad. It is whether the weather was worse than what a reasonable contractor should have anticipated at that location, in that month — and whether the excess landed on work that was controlling the completion date. Those are two arithmetic problems wearing a meteorology costume. Most claims lose on the arithmetic.
A peer-reviewed systematic review puts the exposure plainly: adverse weather delays forty-five percent of construction projects worldwide.16 Nearly half of all projects meet this problem, and the industry's standard response is to start assembling the record after the days are already gone.
#Start with the clause you are actually arguing under
Weather is not one contractual concept. It is four or five, and they do not agree with each other. Before anyone opens a weather database, find out which one governs.
| Document | Where weather lives | What it gets you |
|---|---|---|
| FAR 52.249-10 | Item (x) of the enumerated unforeseeable causes: “Unusually severe weather”1 | Excusable delay — time, not money |
| AIA A201-2017 | §8.3.1, revised to point at adverse weather documented under §15.1.6.22 | Extension of Contract Time |
| ConsensusDocs 200 | §6.3.1, cause (m): “adverse weather conditions not reasonably anticipated”3 | Equitable extension of Contract Time |
| EJCDC C-700 | ¶4.05.C, force majeure — conditioned on critical path impact4 | Contract Times only, not price |
Two things are worth noticing in that table. The first is that every one of them is a time remedy. Weather almost never buys money. If your claim is built to recover cost, it is built against the wrong clause.
The second is the qualifier. “Unusually severe.” “Not reasonably anticipated.” Those are comparative terms, and a comparison needs two operands. The contract supplies one — the actual weather. You are responsible for the other.
#The baseline: what “reasonably anticipated” means in numbers
Some contracts do the work for you. State DOT specifications frequently pre-tabulate the anticipated adverse weather days for each calendar month, and then grant a time extension only for confirmed adverse days that exceed that monthly figure. Wisconsin DOT's standard specification is a clean example of the pattern: submit a request when the number of adverse weather days exceeds the tabulated anticipated number, supported by monthly submittals showing the controlling item of work was delayed.11
If your contract has that table, your baseline argument is over before it starts. Read the table. Count against it. Nothing else matters.
Most private work has no such table. Then the defensible substitute is the federal climate record. NOAA's US Climate Normals are 30-year averages — currently the 1991–2020 period — published specifically as the reference for what is typical at a given location.6 They are free, they are versioned, they predate your dispute, and neither party authored them. That last property is the one that matters. A baseline you produced during the argument is a position. A baseline NOAA published before the project started is a fact.
- Pull the normals for the station nearest the site, not the nearest metro area. A coastal station twenty miles inland is a different climate.
- Convert them into days per month that breach your thresholds, not averages of rainfall inches. A month with normal total precipitation delivered in three storms is not a normal month for a concrete crew.
- Do it at baseline schedule submission, and transmit it. A baseline nobody objected to in month one is very hard to attack in month fourteen.
#Thresholds are a property of the activity, not the project
A quarter inch of rain is nothing to a crew doing interior rough-in and a lost day to a mat pour. “Weather day” is not a project-level concept, and a claim that treats it as one invites the obvious rebuttal: other trades worked.
The good news is that the thresholds mostly already exist, in documents nobody thinks of as weather documents.
| Work | The limit | Source |
|---|---|---|
| Hot-weather concrete | 95°F (35°C) maximum at discharge for general construction; exceeding it requires architect/engineer approval before placement | ACI 305.1-1412 |
| Cold-weather concrete | Cold weather exists when air temperature has fallen to, or is expected to fall below, 40°F (4°C) during the protection period | ACI 306R-1613 |
| Crane operations | No single regulatory wind cutoff. The competent person must adjust for wind, ice, and snow; the operative limit is the manufacturer's, posted in the cab | OSHA 29 CFR 1926.14171415 |
A threshold written down after the weather is an opinion. The same threshold written down at baseline is evidence.
#Observations have to come from somewhere you do not control
Daily reports are necessary and they are not sufficient. They are authored by the party making the claim, which is exactly the objection you will hear. Corroborate them with the federal record, which is free and which nobody can accuse you of writing.
| Product | Contains | Use it for |
|---|---|---|
NWS API (api.weather.gov) | Forecasts, alerts, and observations as a public JSON service7 | Forward-looking exposure, and the contemporaneous forecast of record |
| Local Climatological Data | Hourly and daily station observations from the ASOS/AWOS networks8 | Proving what actually occurred, hour by hour, during the claimed days |
| Storm Events Database | Events of sufficient intensity to cause damage or disrupt commerce9 | Establishing that a specific event was genuinely severe |
| Climate Data Online | The historical archive plus the 30-year normals10 | Building and defending the baseline itself |
Note the split between the first row and the second. The forecast establishes what you reasonably knew and when — which is what makes a mitigation argument possible. The station observations establish what occurred. Claims get muddled when one document is asked to do both jobs.
#A weather day is not a delay until it touches the controlling path
This is where most otherwise-solid records die. Ten excess adverse days on activities with twelve days of float is not a ten-day delay. It is float consumption — real, worth knowing about, and worth nothing as a time extension. EJCDC makes the condition explicit: the entitlement is conditioned on the delay affecting the critical path.4 WisDOT asks for the same thing in different words, requiring the submittal to show the controlling item of work was delayed.11
Which produces an uncomfortable consequence: the float you were quietly proud of is the float that pays for the owner's weather. If you absorb weather into float all spring and then hit a genuinely severe week in autumn with nothing left, the autumn claim is the one that gets scrutinised — and the spring absorption is invisible in the record unless somebody was tracking float consumption as it happened.
AACE's recommended practice on the subject is worth reading in full for exactly this reason. Its definition of adverse weather names float directly: normal weather events that negatively affect worker productivity and/or which may affect a project's critical path or consume float.5 Float consumption is part of the definition, not an afterthought.
#Notice is the link that fails most often
Every document above conditions the remedy on notice, inside a window, in writing. ConsensusDocs routes weather requests through its notice article.3 A201 ties the extension to conditions documented under a specific claims provision.2 The strongest evidentiary package ever assembled is worth nothing filed late, and this is the failure that hurts most, because it is the one that had nothing to do with weather at all.
The practical fix is unglamorous. Notice obligations belong in the schedule as dated activities with the contractual window as the duration, so that a missed filing shows up as a missed activity rather than as a discovery during closeout.
#What this looks like when it is built in rather than assembled afterwards
Every step above is mechanical. Thresholds per activity. A baseline from published normals. Observations from station data. A float test against the current dated schedule. A notice window with a deadline. There is no judgement in the arithmetic — only in setting the thresholds, which is engineering work that happens once.
That is the case for doing it continuously instead of retrospectively. SP4N checks dated weather-sensitive activities against the forecast on each analysis run, fetching National Weather Service data for the project's coordinates at the time of the run, and records overlaps that break an activity threshold as findings with delay-day and probability estimates. Each finding carries a reference into the project record, and a finding whose reference does not resolve is dropped and logged rather than published. You can read how that gate works in why an AI finding without a source is just a rumour, or see the activity-level scoring on the construction delay risk and weather risk pages.
The honest summary is that none of this makes bad weather cheaper. It makes the record contemporaneous, which is the only property of a weather claim that cannot be manufactured later.
Frequently asked
What does “unusually severe weather” actually mean?
It is a comparison, not a category. The federal Default clause for fixed-price construction lists unusually severe weather among the unforeseeable causes that excuse contractor delay, but does not define a threshold. In practice the comparison is against what was reasonably anticipated for that location and month — a contract's tabulated anticipated adverse weather days where one exists, and NOAA's 30-year climate normals where one does not.
Is a weather delay compensable, or only excusable?
Under the standard forms it is generally excusable and non-compensable: you get an extension of contract time, not additional money. EJCDC C-700 states this directly, granting an adjustment to Contract Times only. Cost recovery for weather, where it exists at all, comes from separately negotiated terms rather than from the standard weather provisions.
What weather data should I use to document a delay?
Use two different products for two different jobs. Local Climatological Data from NOAA NCEI gives hourly and daily observations from ASOS and AWOS stations to prove what occurred; the Storm Events Database establishes that a specific event was severe enough to disrupt commerce. Keep the contemporaneous NWS forecast separately, as evidence of what you reasonably knew and when.
Do I have a claim if the weather days only consumed float?
Generally no. The standard forms condition a time extension on impact to the critical or controlling path, so adverse days absorbed by float do not produce an extension. They are still worth tracking, because float consumed early is float unavailable when a genuinely severe event arrives later.
Is there a standard wind speed at which crane operations must stop?
No. OSHA does not publish a numeric cutoff, notes that load charts generally do not account for wind speed, and requires the employer to determine unsafe speeds using the crane manufacturer's wind and derating data, which must be available in the cab. The citable limit is therefore machine-specific and belongs in the schedule as an attribute of the lift.
Sources
- 1FAR 52.249-10 — Default (Fixed-Price Construction)Item (x) of the enumerated unforeseeable causes reads “Unusually severe weather, or”.
- 2Summary: A201-2017, General Conditions of the Contract for Construction
- 3ConsensusDocs 200 — Standard Agreement and General Conditions Between Owner and Constructor§6.3.1, cause (m): “adverse weather conditions not reasonably anticipated”.
- 4Force Majeure Events: Abnormal Weather and Other Uncontrollable Delays
- 5Recommended Practice 84R-13, Planning and Accounting for Adverse WeatherExplicitly does not address legal or forensic delay-claim analysis.
- 6U.S. Climate NormalsCurrent release covers 1991–2020.
- 7NWS API Documentation
- 8Local Climatological Data (LCD)
- 9Storm Events Database
- 10Climate Data Online (CDO)
- 11Standard Specifications §108.10.2.2 — Extension of Contract Time for Severe Weather
- 12ACI FAQ — maximum temperature limits for hot-weather concreting (ACI 305.1-14)
- 13ACI 306R-16, Guide to Cold Weather Concreting
- 1429 CFR 1926.1417 — Operation (Cranes and Derricks in Construction)
- 15Green Job Hazards — Crane, Derrick and Hoist Safety
- 16Weather-Related Construction Delays in a Changing Climate: A Systematic State-of-the-Art Review