Each day gets a 0-100 score for cutting that day, judged by the drying window that follows it - how much drying power the weather gives you before rain, dew, and time run out. It rolls up to a plain call: Prime cut (72+), Good (52+), Marginal (34+), or Don’t cut. Rain in the window is the heaviest penalty and it gets worse the drier the hay is - rain on nearly-cured hay leaches quality worst. Tap “Why this call?” on the forecast to see the exact breakdown.

Instead of trusting one forecast, HayWatch pulls rain forecasts from several national weather services and checks whether they agree:

• ECMWF - European Centre (widely rated the most accurate global model; ~7-day range here)
• GFS - US NOAA (its near-term blend includes the 3 km HRRR model)
• ICON - German Weather Service (DWD)
• GEM - Environment Canada
• Météo-France - the French national model

When they all see rain in your window, that’s High confidence - wait. When they split, it’s Low confidence - the forecast isn’t settled, so don’t bet the crop on it. The Forecast models panel shows what each one says for your window. (Most consumer weather apps are proprietary blends built on these same government models - HayWatch just shows the sources and their spread directly.)

A percentage is coverage × confidence, not "40% chance your field gets wet." In summer it usually means "showers will form and cover ~40% of the area" - one town gets soaked, the next stays dry. So HayWatch labels each rainy day:

• Widespread - a real system, the models agree, meaningful totals. The whole county gets it; don't count on dodging it.
• Scattered - pop-up showers, models split, low totals, hot muggy afternoon. Hit-or-miss: your field might dodge it, but it's a gamble.

For the scattered case there's no forecast on earth that can tell you days out whether your exact field gets the cell - so on those days, watch the radar (below) the morning of.

Live precipitation radar centered on your field (free, from RainViewer), with rings at 25 and 50 miles. Scrub or play the last ~2 hours to see which way cells are moving - that's your warning time on a scattered day. It only looks ~an hour ahead, so it's a same-day, about-to-cut tool, not for planning days out.

Reference evapotranspiration (ET₀) is one number that folds sun, heat, wind and dryness into how fast the air pulls moisture out of the swath. More ET₀ = faster, safer cure. It’s the honest “drying” signal behind the predicted dry-down days. Weak ≈ under 3 mm/day, Strong ≈ 5 mm+/day in this region.

Predicted dry-down is the calendar days from cut to baling moisture, from the drying power over your window. It’s tuned to this region: conditioned grass runs ~2 days on a good stretch, 3 mediocre, 4 with heavy dew. Thick-stemmed legumes (alfalfa, clover) dry slower. A mower-conditioner (crimped/rolled) saves about a day on legumes and a little on grass - pick your equipment so the estimate matches your setup.

The plan shows each day’s dew-off (morning, when the swath is workable) and dew-set (evening, stop baling) - plus days when dew lingers and nothing dries. When rain is coming, it shows when it arrives (“rain from ~2 PM”), so you know your deadline to get off the field, not just which day it’ll rain.

Baleage/haylage is wilted ~a day to 45-55% moisture, then wrapped wet - far more rain-tolerant than dry hay, which needs the full clear stretch down to ~16-18%. If the forecast won’t give you a dry-hay window, baleage is often the salvage path. Pick it under Making.

Everything runs in your browser. Your fields, coordinates and log stay on your device - nothing is sent to a server. It installs and works offline (last-loaded forecast). All data comes from free public sources (Open-Meteo, incl. the national models above). The scoring weights are informed starting points, not validated science - always confirm bale moisture with a probe, and treat this as a planning aid, not a guarantee.