Hay Drying Weather: Forecasts and Cutting Window Planning

Overnight dew points below 50°F produce minimal moisture reabsorption. The crop may gain 1–3% moisture overnight from slight condensation but dries back rapidly in the first 1–2 hours of the next morning. In arid western climates where summer dew points are consistently 30–45°F, hay can sometimes be baled in the early morning after an overnight drying period without significant reabsorption concern.

In humid midwestern and eastern regions where summer dew points are consistently 60–70°F, overnight reabsorption is a major yield and quality factor. Hay that dried to 18% by 5 PM can return to 28–32% by 7 AM the next morning. This means the effective drying window is only the daylight hours — and baling must occur before dusk on the day the crop reaches baling moisture, not the following morning. Plan baling schedules around this constraint in high-dew-point climates.

Services such as DTN/Progressive Farmer, AgWeather, and Climate Corporation offer field-specific forecasts with hourly RH, temperature, wind, and precipitation probability. Many include a “hay drying index” or equivalent composite metric that translates the raw variables into a single drying potential score. These services are subscription-based but typically cost $100–$300/year — justified for operations where a single rained-on cutting represents $2,000+ in quality losses.

NOAA’s National Digital Forecast Database provides hourly forecasts for any GPS coordinate in the U.S. at no cost through api.weather.gov. The API provides temperature, RH, dew point, wind speed, precipitation probability, and sky cover for each hour, 7 days forward. A simple spreadsheet that inputs your field coordinates and pulls this data provides better field-level forecasting than any app for the drying period analysis described in this guide.

A simple on-farm weather station ($200–$600) recording temperature, RH, dew point, and wind gives the actual conditions at your field rather than forecast conditions. Historical on-farm records are the most valuable tool for calibrating forecast-to-actual differences specific to your location — learning your microclimate’s systematic biases from the regional forecast makes every subsequent cutting decision more accurate.

On hay above 35% moisture: minimal additional damage — the crop was already wet and the rain adds limited total water. On hay at 15–25%: more damaging, as the rain rewets dried stems that had lost their waxy cuticle protection. Response: wait for surface dew to dry (typically 2–4 hours after rain stops), then ted if crop is above 30% moisture. Bale when moisture probe confirms target range.

Significant protein and soluble carbohydrate leaching occurs from rain contact on hay below 40% moisture. Quality loss is real and measurable on a forage test — expect 5–15 RFV point reduction on leached hay. After rain stops, allow at least 6 hours before entering the field to allow surface water to drain. Ted the windrow to accelerate re-drying. Test moisture before baling — rained-on hay often has non-uniform moisture with dry surface and wet core. If a second rain is forecast within 24 hours, consider baling at slightly elevated moisture with hay preservative to prevent further leaching.

Heavy rain on curing hay causes major quality loss — leaching, physical damage to the mat structure, potential mold initiation at the windrow base, and a significant RFV reduction that drops Premium-grade hay to Good or below. Reassess market destination after a heavy rain event — hay that was intended for horse or export premium markets may need to be redirected to livestock feed markets at a lower price point. A forage test after re-drying provides the actual quality data needed for accurate market decisions.

Cutting in the morning maximizes the drying time available on the first day. A crop cut at 9 AM has 8–9 hours of peak-sun drying before late afternoon humidity begins rising. The disadvantage: morning dew may still be present on the crop at cutting time, adding initial moisture load. Wait until dew evaporates from the crop surface (typically 8:30–9:30 AM in summer) before cutting to avoid mechanical dew-spread during mowing. A morning cut requires a corresponding morning rake and afternoon bale — the full workflow must fit within the single day’s drying window in high-dew-point climates.

Afternoon cuts allow dew evaporation before cutting but provide less same-day drying time. The advantage is that the mowed crop has the highest sugar content in the afternoon (photosynthesis has been running all day), which can support more efficient fermentation for silage applications. For dry hay production in humid climates, afternoon cuts produce less same-day progress than morning cuts. In arid western climates where overnight moisture reabsorption is low, afternoon cuts are viable since the crop dries adequately the following day without significant overnight setback.