Your competitor who runs NOAA historical data before pricing? They’re not smarter than you. They just stopped pretending that gut feel is a risk model.
We modeled a 240-day Houston site work scope recently.
Simple 30-year average: 31 non-workable days
Recency-weighted P80: 52 non-workable days
That’s 21 extra days. At $15-20K/day — that’s $300K+ in unpriced exposure on one scope.
The mistake most estimates make: treating heat as a shutdown event.
A crew working 6-hour days in a Houston July doesn’t show up as a weather day in your logs. But they’re delivering 25-40% less output than your schedule assumes. That compounds fast.
Texas isn’t one climate — it’s four.
Gulf Coast, DFW, West Texas, South Texas all have completely different risk profiles. What works in Houston will underprice a Panhandle job and overprice a San Antonio job.
When you bring actual workable-day counts and P50/P80 ranges to a bid, the conversation with the owner changes.
You’re not defending a contingency. You’re presenting data.
Full breakdown with visuals here: xyloclime.com/blog/how-to-ac…
Most weather contingencies in construction bids are wrong.
Not because estimators are careless — because gut feel calibrates to memorable years, not actual historical distributions.
Here’s how to price weather risk properly:
The framework in short:
1.Identify your weather-sensitive activities (earthwork, concrete, envelope)
2.Pull historical data for the actual months your schedule occupies
3.Apply recency weighting
4.Evaluate P50 + P80 by phase
5.Separate shutdown days from productivity
One thing most estimators miss even when they do pull historical data:
A wet year from 2005 shouldn’t weigh the same as 2023.
Climate baselines drift. Recency weighting corrects for that — recent years are more predictive than a flat 30-year average.
A real example:
180-day earthwork scope, DFW, Oct–March
Simple 30-yr average: 22 non-workable days budgeted
Recency-weighted P50: 28 days
Recency-weighted P80: 36 days
That 14-day gap at $18–22k/crew day = $250–300k in unpriced exposure.
That’s not a margin of error. That’s a gap
Weather risk isn’t a single number. It’s a range with a shape.
P50 = what a typical year looks like
P80 = worse than 80% of historical years (~1 in 5)
P90 = near-worst case
The gap between P50 and P80 is your actual contingency range. Most bids never calculate it.
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