Frost
How to use Frost
Search a place, read the chance, check the hours, then compare the dew point spread with the overnight low.
On a clear, still night the ground radiates heat away and chills the air resting on it. When that air reaches the dew point, moisture condenses — dew if it stays above freezing, frost if it drops below.
1. Find somewhere
Search for a town, glen, hill, or dark site. Tap the long box and type a name, then tap the name that appears.
The round button uses this device’s location. Choose on a map drops a copper pin. Tap the map to move it, then tap Use this spot. The place name shows in the search box.
Four places start under the search box, the same ones as Lid: Cairngorms, Galloway, Glencoe, and the Lake District. Tap a tile to switch. Each tile shows the chance at that spot. You can keep up to eight.
2. Read the number
The large copper number is the chance of frost or dew overnight at that one spot. It is the strongest hour between dusk and dawn, not an average of the whole glen.
Under the number is a plain word: Very likely, Likely, Possible, Low chance, or Unlikely.
A line under that says whether the morning is worth getting up for. Beside it, the overnight low and the dew-point spread. Compare those two. A small spread and a low near freezing is the picture you came for.
It’s a forecast of the ground, not a promise of frost.
3. Look through the night
A row of bars runs from dusk to dawn. Taller bars mean a higher chance. Copper means 60% or more. Tap a bar for that hour’s air, ground, dew point, wind and cloud.
A dot under an hour marks true dark, when the sun is far enough down that twilight has left the sky.
4. See what is in the way
Three rows: clear skies, calm air, and dew point spread. Each has a word and a number. Longer copper means more of that thing is present.
Frost wants all three. Cloud or a breeze keeps the ground from cooling. A wide spread means the air would have to fall a long way before anything condenses.
5. Explore the explanation
Temperature with height is a copper line. Where it bends warmer above colder air, that is the lid — the same bend Lid draws — with the cold ground layer added. Heights are spaced so that thin layer stays visible. They are not drawn to scale.
On the forecast, tap Why this number and How this percentage is made. Tap again to close them.
6. Save places
Save place puts the open spot into a shortcut. Choose Instead of a place to switch one out, or Add as another while there is room. Remove from saved takes the current place off the row. Tap a name in the Saved places box to open it. Rename and Remove are there too. They stay on this device.
7. Other things you can do
Switch °C or °F at the top. Heights follow: metres with °C, feet with °F.
Share, on the time card, draws a map of the place with the number, the word, the reason, the hours, and a link back to this spot. Share sends the picture. Save picture keeps it. If the share sheet does not open, the link is copied.
Under the night, Lid and Transparency sit side by side, with Sky Contours under them. Each card is a short summary. Open the link for the full reading at this same place.
A last note
Frost is for information, not a safety forecast. If you are driving, walking in frost, or concerned about ice, use a local forecast as well.