Loam
The rain stops. Drying starts.
Once rain moves out, the trail is still losing water. What happens next depends partly on the conditions at the surface.
Sun warms the ground. Wind moves air across it. Neither one works alone, and neither guarantees that a trail is ready. But both can change how quickly surface moisture disappears.
Why this matters
A trail under trees and a trail in an open field can be only a short distance apart. Their recovery can still look very different.
Shade is not the same thing as wet
Shade does not automatically mean a trail is closed or unusable. It means the surface may get less direct solar energy after rain, which can slow drying compared with otherwise similar exposed ground.
Dense trees can also reduce airflow near the ground. That matters because moving air helps moisture leave the surface. On a cool day, a shaded section may have fewer opportunities to warm and dry.
Sun helps, but it cannot fix everything
A sunny trail can dry quickly at the surface while remaining soft underneath. This is especially important after a substantial storm or when the ground was already wet.
That is why a trailhead that looks dry in the afternoon can still have soft tread in low spots. Surface appearance is useful. Tread firmness is better.
Wind is easy to overlook
Wind changes the air right above the ground. It can help move moisture away from a wet surface, which is one reason an exposed section may recover faster than a sheltered one.
But wind is not a magic drying switch. If the soil is saturated or water is trapped in a low spot, a breeze cannot make that water disappear instantly. Drainage and soil still matter.
Look at the whole combination
Open and sunny
More direct sun and airflow can help the surface dry, especially when the weather is warm.
Open but flat
Sun helps, but water can still collect where the trail has little slope or poor drainage.
Shaded and sloped
Shade can slow surface drying while the slope helps water move away. Neither factor tells the whole story alone.
Shaded and flat
Less direct sun and little grade can make a wet section slower to recover, particularly in cool weather.
Use this as context, not a shortcut
You do not need to memorize a drying formula. The useful takeaway is that the weather after the rain matters too. A warm, breezy afternoon can change a trail faster than a cool, cloudy one.
Check the official trail status, check the current network condition, and then look at the tread when you arrive. The goal is not to predict every inch of dirt. It is to make a better decision before your tires get there.
The science behind the estimate
Loam starts with a simple physical fact: a trail does not dry just because the rain stops. Water has to enter the ground, move through or across the soil, and leave the trail environment. How quickly that happens depends on the soil, terrain, vegetation, recent weather, and how wet the ground already was.
Soil controls infiltration
Soils do not accept water at the same rate. USDA hydrologic soil groups range from high-infiltration soils such as deep sands and gravels to very slow-infiltration soils associated with clay, high water tables, or restrictive layers. Typical infiltration-rate ranges used in the hydrologic-group framework run from more than 0.30 in/hr for Group A to less than 0.05 in/hr for Group D when thoroughly wet.
Previous rain still matters
A storm does not start with an empty soil profile. USGS notes that soil already saturated from previous rainfall cannot absorb much more, so a larger share of the next storm becomes runoff. Recent weather therefore matters even when the latest storm was not especially large.
Terrain changes the water path
Slope changes how quickly water can move away from a surface. Low spots, drainage features, and trail geometry can change where water collects or leaves the tread. Soil classification and slope are separate pieces of the landscape, which is why both matter to a trail-condition model.
Drying is a water budget
After rainfall, water can remain in the soil, move downward or sideways, run off, or return to the atmosphere through evaporation and plant transpiration. Soil-water-balance models use these processes to estimate changing soil moisture and net infiltration over time.
Why Loam is not a rain timer
There is no useful rule that says every trail becomes rideable after the same number of dry hours. Starting moisture, infiltration behavior, terrain, canopy, and weather after the storm all change the answer.
That is the problem Loam is designed to estimate. The model combines public soil and terrain information with recent weather and network characteristics to estimate how conditions are changing. It is a model of likely trail conditions, not a sensor embedded in the dirt, and it never overrides an official closure.
What the research says
USDA and USGS hydrology work treats infiltration, soil moisture, runoff, canopy, land cover, slope, and evapotranspiration as interacting parts of the water cycle. Recent trail research adds an important piece: rainfall intensity and accumulated rainfall can strongly affect runoff and sediment generation on recreational trails, while wet conditions make trail surfaces more vulnerable to degradation.
USDA NRCS: Hydrologic Soil Groups
Soils are classified by infiltration and runoff behavior when thoroughly wet. The framework distinguishes four main groups and dual drained/undrained classes.
NRCS National Engineering Handbook →USGS: Infiltration and the Water Cycle
Explains how soil characteristics, saturation, land cover, slope, and evapotranspiration affect where precipitation goes.
USGS Water Science School →USGS: Soil-Water-Balance
A published water-budget model that estimates soil moisture, net infiltration, evapotranspiration, and canopy interception from gridded environmental data.
USGS SWB Version 2.0 →NRCS: RUSLE2
A USDA model for estimating soil loss caused by rainfall and associated overland flow, connecting rainfall and runoff to erosion risk.
USDA NRCS RUSLE2 →Fang & Ng, Journal of Environmental Management, 2026
A year-long field study found cumulative rainfall and maximum daily rainfall predicted runoff and sediment yield on recreational trails, with maximum daily rainfall the stronger predictor in that study.
Read the research →These sources describe the physical processes and research Loam draws from. They do not describe Loam's proprietary model or disclose its weights and thresholds.