Loam
The weather is only one part of the story
When two trails are close together, it is natural to assume they should have similar conditions. If it rained at one, surely it rained at the other.
That part may be true. What happens next is where things get interesting. Water interacts with the soil, vegetation, slope, and shape of each trail. Those differences can be enough to change the riding surface even when the rain was identical.
Think about the ground, not just the sky
A rain cloud covers an area. A trail has a very specific piece of ground underneath it.
Four reasons conditions split apart
Different soil
One network may have coarse, rocky ground while another has finer soil that holds water near the surface. The same rainfall does not produce the same tread.
Different canopy
Trees change how much sun and wind reach the trail after rain. A shaded section can remain damp while an exposed ridge nearby dries quickly.
Different slope
Gravity is useful for drying trails. Water generally moves downhill, so steeper ground can shed water faster than a flat section where it can collect.
Different drainage
Trail shape matters. A tread that moves water off to the side recovers differently from a flat section that lets water sit in the riding line.
Distance is a poor shortcut
Trail riders often learn local rules of thumb. This trail is always good after a day. That one needs three days. Those rules can be useful when they come from years of riding the same ground, but they are not universal.
A storm that arrives after a long dry spell is different from the same storm after a wet week. A cool, cloudy day after rain is different from a warm, breezy one. The calendar says both are one day later. The ground does not care about the calendar.
This is why Loam looks at networks individually
Loam does not treat a whole region as one piece of dirt. The condition estimate is tied to the network and the physical characteristics that affect how it handles water, along with recent weather.
That is useful when you are deciding between two places that are both technically open. One might be in better shape today. The point is not to rank trails permanently. It is to give you a better read on what the ground is likely doing right now.
Still check the actual trail
A model can help you decide where to look. It cannot see the exact rut in front of your wheel. Check the land manager's status first, then use the condition estimate as another piece of information. If the tread is soft when you arrive, do not ride it just because a nearby network looks good.
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.