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What to know: NOAA’s September 10, 2026 forecast gives this winter’s El Niño a 75% chance of being the strongest since records began in 1950. The heaviest rain is expected January through March across coastal California and the Southeast, while the North tilts warmer with less snow. It arrives with record diesel prices, rising interest rates and a labor shortage, so every lost day costs more than usual. Construction contracts typically set weather days from historical averages. Here is where the weather is likely to land, what it costs, and what to change this fall.
The El Niño building in the Pacific right now may turn out to be the strongest ever recorded. NOAA’s September 10 update puts the odds of a very strong event this winter above 90%, with a 75% chance it beats every El Niño since records began in 1950. If you’re building anything this winter, whether it’s a house, an apartment building or a data center, that forecast is going to show up in your costs.
The timing is the problem. NOAA’s seasonal outlook has the rain building slowly and peaking from January through March across coastal California and the Southeast. A project that breaks ground this fall will spend those months as an open excavation, then a foundation, then a frame with no roof on it, which is when water does the worst damage and lost time is hardest to make up.
No slack left
In a normal year the industry absorbs a wet winter without much drama. Carrying a project an extra month is affordable, the crew that got rained out comes back Monday, and materials cost about the same in March as in January. None of that is true right now.
The Fed raised interest rates on September 16 for the first time since 2023. Construction loans usually carry rates that move with the Fed’s, so nearly every project under way got more expensive to carry overnight. Diesel crossed $6 a gallon this month for the first time ever, and EIA’s national average on September 14 was $6.29, up $2.55 in a year. Yikes. Excavators, pumps, dump trucks and jobsite generators all run on it. Construction materials are up 8.9% over the past year according to Associated Builders and Contractors, so anything that gets soaked and replaced is bought at today’s price.
Labor is what turns a lost day into a lost week. In the Associated General Contractors’ survey released September 3, 42% of firms said worker shortages had already delayed their projects. A crew that gets rained off your job in February goes to another one, and when your site dries out you get back in line.
The weather is even squeezing the supply chain. The same El Niño that’s forecast to soak the South is drying out Panama, where the canal authority has cut daily ship crossings from 36 to 32 for lack of rain. That canal is the main water route for Asian cargo headed to East and Gulf Coast ports, so if your electrical gear is coming by ship, your delivery date now depends partly on rainfall in Panama.
Diesel might come back down, and the Fed might stop at one hike. I wouldn’t build a schedule around either, and there isn’t much you can do about them from a jobsite anyway. The weather is the one item on that list you’ve been warned about in time to act on.
Where it lands
The Southeast
The Southeast has the loudest numbers on the map. NOAA puts the odds of a wetter-than-normal season above 60% across parts of the region for November through January and keeps them elevated through March. The record backs it up. During the 1997-98 El Niño, the one this event is expected to beat, the Southeast had its wettest winter on record and Florida got more than double its normal rain. El Niño also tends to quiet the Atlantic hurricane season, but a quiet hurricane season and a dry winter are different things.
Much of the region builds on clay, which can’t be compacted wet, and in January there isn’t enough sun or heat to dry it out. An inch of rain that costs a day in July can cost the better part of a week in winter. On the biggest sites the math gets ugly fast. CBRE has small data center leases asking more than $215 per kilowatt per month, and at even half that rate a one-month slip on a 100-megawatt building is more than $10 million of rent showing up late.
Coastal California
California’s signal peaks late. NOAA has the odds of a wet winter above 50% along the coast from December through April, and its forecasters noted that recent El Niños of this type delivered their heaviest rain late in the season. LAX got 13.79 inches in February 1998 alone.
Los Angeles also has an unusual amount of work sitting out in the open. By early July the county had issued about 3,000 building permits in the Eaton fire area and roughly 100 homes were finished. That leaves thousands of wildfire rebuilds under way, mostly wood frame, many on or below slopes that burned less than two years ago.
Cold climates
In the North, winter is a line item. Concrete needs protection once temperatures drop below about 40°F, which means tenting the work, heating the enclosure around the clock and insulating the pour while it cures. The Federal Highway Administration says that kind of protection can more than double the cost of a concrete job. Contractors price it into winter bids based on a typical winter, so the snow and cold they assume can move a bid a long way.
This winter doesn’t look typical. NOAA favors a warmer-than-normal winter from the Pacific Northwest to the Northeast, and its snowfall record shows El Niño cutting snow around the Great Lakes, interior New England, the northern Rockies and the Pacific Northwest. The most recent El Niño winter, 2023-24, gave eight states from North Dakota to New Hampshire their warmest winter on record. A bid built on a normal winter may be carrying protection costs that never show up. It runs the other way in the Southern Rockies, where strong El Niños tend to bring more snow, so Denver and Salt Lake City should be reading a different forecast than Minneapolis.
The weather days in your contract describe a climate that’s gone
Here’s how construction contracts usually handle weather. They allow a set number of bad-weather days per month, based on a historical average for the site. If the actual weather is worse, the contractor typically gets extra time and nobody gets extra money. The contractor pays to keep the site open longer, the owner pays for a later opening and more interest, and since neither side priced it, the argument usually ends up in a legal claim.
Those averages have a problem this year. Some contracts use the last ten years of weather, an approach the Army Corps of Engineers spelled out in a regulation dated October 31, 1989. By NOAA’s current index, seven of the last ten winters were La Niña winters, which run dry across the South, so that average is biased dry going into a winter NOAA expects to run wet. Other contracts use NOAA’s 30-year normals, and NOAA ran into trouble with those first. This February the agency changed the way it measures El Niño, because the old method compared the Pacific to a 30-year average and the oceans had warmed too fast for the average to keep up. The people who write the forecast stopped trusting a 30-year average for their own work. Plenty of construction contracts still rest on one.
The ten warmest years in NOAA’s global record have all come since 2015, and warmer air holds about 7% more water per degree Celsius, so a storm on the same track as 1998 has more rain to work with. We had a chance to prevent the warming and we blew it. What’s left is building for the weather it produces, and the first step is putting a real number on it.
Design decides how much winter you absorb
By the time anyone is adding weather days to a schedule, how much winter the project will absorb has largely been decided, by design choices nobody evaluated for weather. The big one is how long the building sits open to the sky. A five-story wood-framed building can leave its structure exposed for months, and wet framing has to dry out before anyone can insulate or hang drywall. Wall panels and trusses built in a factory, or precast concrete, can close a building weeks sooner. The site plan matters as much. Put the permanent drainage in first and the site sheds water all winter. Too many projects leave it for last.
Those comparisons rarely get made, because early in design nobody has the cost and schedule consequences in front of them. That’s changing fast. At cove we do in days what typically takes weeks, and across most building types we run 50% to 60% faster, largely by moving decisions like these to the front of the process, where they’re cheap to change and they take risk out of everything downstream. The forecasts are improving on the same curve. NOAA’s AI-driven global weather model, which went into service last December, produces a 16-day forecast in about 40 minutes using 0.3% of the computing power the old one needed. The information about the weather and the tools to design around it get better every year. The weather clause in the contract is the part that hasn’t moved.
What to do with the fall
There’s still time to move real exposure, and everything below is cheaper in October than in January.
Get out of the ground early. If excavation and foundations fall between January and March on your schedule, find out what it takes to pull them into the fall. An early site and foundation permit package can keep the dirt work from waiting on the full building permit.
Protect what stays exposed. Stabilize the ground under the building and the site roads before the rain starts, and treat getting the roof on and the walls sealed as a hard deadline with spare time in front of it.
Test the schedule against real winters. NOAA’s daily rainfall records are free. Run your schedule against January through March of 1998, 2016 and 2024 for the nearest weather station, see what breaks, and set weather days and contingency to match. In cold climates, ask what winter your bids assume, because the concrete protection is priced off it.
Read the fine print and make the calls. Find out what average your weather clause uses and who pays when the weather beats it. Ask your lender how many months of delay the loan can take at today’s rates, check when the insurance covering the building during construction runs out, and order anything that’s coming by ship early.
A forecast is still a forecast
NOAA is careful about this and I should be too. Even a record El Niño shifts the odds and guarantees nothing at your site. The 2015-16 El Niño was about as strong as 1997-98, and Los Angeles got a little over half its normal winter rain.
But construction prices probabilities every day. Contingency and insurance are both bets on things that might happen. A better-than-even chance of a wetter-than-normal winter over your site, published months ahead, is better information than the typical budget line ever gets.
NOAA updates its forecast every month. How often does anyone update the weather days in your schedule?
About cove’s Principal Architect Patrick Chopson, AIA
Patrick Chopson, AIA, is Co-Founder and Principal of cove, an AI-powered architecture firm transforming how buildings are designed and delivered. A licensed architect with 20+ years of experience, technologist and building scientist, Patrick focuses on the intersection of AI and Architecture.
He previously co-founded the building performance consultancy Pattern r+d and co-authored Build Like It’s the End of the World (Wiley, 2025), a guide to decarbonizing AEC. His work has been featured in Architect Magazine, TechCrunch, and ArchDaily, and he regularly collaborates with developers and industry leaders on next-generation solutions.