When do Oklahoma foundations move during the year?
In short: Oklahoma's clay soils follow the weather through the year: they swell during wet springs, shrink in hot, dry midsummer, and partly rewet with fall rains. Foundation cracks often open in late summer and narrow in spring. The exact timing shifts from year to year with drought and wet spells.
Why does the calendar matter?
Expansive clay swells when water enters and shrinks when it dries, and uneven moisture under a house causes differential movement 7. Because Oklahoma's rainfall and evaporation follow a seasonal rhythm, so does much foundation movement. A crack that closes in April and reopens in August is a classic sign of moisture-driven movement; see cracks that open and close seasonally.
What is the general seasonal pattern?
| Season | Weather pattern | Typical soil behavior |
|---|---|---|
| Winter (Dec–Feb) | Shorter, milder winters than the northern Plains; freezing rain occurs regularly, especially in the southeast 12 | Low evaporation; frozen soil is rare and brief 1 |
| Spring (Mar–May) | Rainfall rises; three-fourths of tornadoes occur April–June 1 | Soil rewets, clay swells, cracks may narrow |
| Late spring to early summer (May–Jun) | Often very wet; flooding most common in the rainy spring and fall months 1 | Highest moisture; perched water and edge lift possible |
| Midsummer (Jul–Aug) | Rainfall relaxes in July and August; long, hot summers 1 | Fast drying, perimeter shrinkage, cracks widen |
| Fall (Sep–Nov) | A secondary rainy and severe-weather season 1 | Partial rewetting |
Most of Oklahoma's precipitation falls in spring and summer, and the state ranges from under 20 inches a year in the west to more than 50 in the southeast 2. Average annual lake evaporation, from about 48 inches in the east to 65 inches in the southwest, exceeds average rainfall in those areas 1. That imbalance is why soils dry so quickly in hot spells.
How much does it vary year to year?
The seasonal pattern is a tendency, not a rule:
- Wet years: May and June 2019 together averaged 15.52 inches statewide, the fifth-wettest such period on record 5.
- Dry years: In 2011, Tulsa had very little rain in June and July, and the state had its third-driest summer on record 6.
More on multi-year swings is on the drought and wet cycles page.
How can soil moisture be tracked through the year?
The Oklahoma Mesonet reports daily soil moisture as a fractional water index from 0 (very dry) to 1 (very wet) 34. A few points from the sources:
- Soil moisture falls faster in hot, dry periods 3.
- Readings at several depths show how far rain has soaked in 3.
- Winter maps can have gaps because sensors can't read frozen soil 4.
Recording the date, recent rainfall and soil moisture with each elevation survey makes it easier to compare measurements taken in different seasons. Details are on the Mesonet guide.
Related
- Drought and Wet Cycles
- Mesonet for Foundation Pros
- Shrink-Swell and Active Zone
- Freeze-Thaw and Frost Depth
- Monitoring Program
Common questions
When are foundation cracks worst in Oklahoma?
Cracks from shrinking clay tend to open in hot, dry stretches, which in Oklahoma usually means July and August, when rainfall relaxes and evaporation is high. They often narrow again when spring or fall rains rewet the soil.
Why did my cracks close up in the spring?
Spring is one of Oklahoma's wettest periods, and clay swells as it takes on water. A crack that closes has not necessarily been fixed; it may reopen the next time the soil dries.
Does frost move foundations in Oklahoma?
Less than in northern states. Oklahoma winters are shorter and milder than the northern Plains, and the Oklahoma Climatological Survey describes frozen soil as infrequent, shallow and brief.
Does the season affect foundation measurements?
Comparing measurements taken under similar soil moisture gives the clearest picture. Recording the season and current Mesonet soil moisture with each survey helps make later readings comparable.
Sources
- Oklahoma Climate Oklahoma Climatological Survey
- Oklahoma - State Climate Summaries 2022 NOAA National Centers for Environmental Information
- Tracking Drought Using Soil Moisture Information (BAE-1541) Oklahoma State University Extension
- 1-day Average 4-inch Bare Soil Fractional Water Index Oklahoma Mesonet
- Oklahoma Monthly Climate Summary: June 2019 Oklahoma Climatological Survey
- 2011 Drought National Weather Service, Tulsa
- Residential House Foundations on Expansive Soils in Changing Climates HUD Office of Policy Development and Research (Cityscape, Vol. 25 No. 1)
Was this page helpful?
Thanks. Your note goes straight to the person who maintains this library.