Every other frost page explains what frost is. None of them answer the only question you have at 6:40 in the morning, which is when you can tee off. Answer four things and get a window.
Frost is frozen dew, and it melts for two reasons: the air warms up, and the sun hits the leaf. On a clear, calm morning the sun does most of the work, which is why the honest baseline is about an hour after sunrise on open, sun-exposed holes. Everything else is an adjustment to that anchor.
Sky is the biggest lever, because it controls how much solar energy reaches the turf. Overcast mornings can push the lift an hour later than a clear one at the same temperature.
Wind usually helps. Moving air mixes warmer air from above down onto the surface, so the turf never gets as cold overnight and thaws faster once the morning turns. A dead calm, clear night is the classic setup for the longest delay.
Shade and low ground are why the course does not open all at once. A green in full morning sun can be playable while a tree-lined tee two holes later is still white, and cold air pools in low spots. The superintendent waits for the last one.
Temperature matters less than most golfers expect, because the number on your phone is measured a few feet off the ground. On a clear calm night the turf surface radiates heat away and runs several degrees colder than the air, so 35 degrees at the clubhouse can still mean frozen grass. Temperatures also keep dropping for a short time after sunrise.
Because that reading is not the grass. Surface temperature on a clear, calm morning runs several degrees below air temperature, and the crew has to protect the coldest turf on the property, not the warmest.
Frost is frozen water in and around the leaf. Footsteps rupture the cell walls, and the plant stops functioning normally. The damage appears days later as footprint-shaped dead turf that heals slowly and lets disease and weeds in. That is why maintenance stays off it too.
Anywhere from fifteen minutes to about three hours, and it changes day to day on the same course. That range is exactly why a window is more useful than a rule of thumb.
Radar tells you about rain, not about frost, and rain is the other half of the problem. If you want to know whether the course is soft, cart-path-only, or genuinely dry, that is what DryLies is for: conditions reported by the people who were just there, plus how a specific course's soil actually drains.
This calculator stays free and needs nothing from you. What it cannot tell you is whether the course is actually playable once the white burns off, because that is rain and drainage, not sun. The DryLies app answers that part: turf status per course, cart rules, and the nearest dry courses when yours is soaked. Free on iPhone, no account required.
If you want the phone to tell you instead of the other way round, DryLies+ is $4.99 a month: a push the moment a course you favorited flips dry, a frost or aeration alert when the course posts one, and a seven-day turf forecast so you pick the right morning in the first place. Cancel anytime.
Today's status is free either way, in the app and on the web. Nothing you typed into the calculator above is stored, sent, or attached to any of this.
Built on standard turf guidance about frost formation and thaw: frost forms near the coldest point of the night, usually around sunrise, under clear skies and calm winds; the turf surface runs colder than the measured air temperature; and sun-exposed areas thaw well before shaded or low-lying ones. See Ask the Superintendent and Understanding Frost Delays. Nothing you enter here is stored or sent anywhere.