Frost risk depends on more than tonight's forecast low — clear skies and calm wind let heat escape fast, while cloud and breeze hold it in. Enter your postcode below for a 5-day forecast plus an estimated frost risk for tonight, built from Met Office data. This is a helpful estimate, not an official Met Office warning — always check the Met Office directly for official warnings.
How We Estimate Frost Risk
Our Estimated Frost Risk is calculated from four things the Met Office forecast gives us: tonight's forecast minimum temperature, humidity (used to estimate dew point), wind speed and cloud cover. Clear, calm nights lose heat to the sky fastest — that is classic radiation-frost weather — while cloud cover and breeze both work against a hard frost forming, even on a cold night. We combine these into a category (None, Low, Moderate or High) and deliberately round up when the inputs are borderline, because the cost of an unprotected frost-damaged plant is higher than the cost of an unnecessary fleece.
This is an algorithmic estimate for everyday gardening decisions, not an official Met Office frost warning. For official Met Office warnings, check their own severe weather page directly.
Soil temperature: an honest estimate, not a rolling mean
You may see other sites quote a “7-day rolling mean” for soil temperature. We don't, because the Met Office daily forecast we use only returns one past day plus a handful of forecast days — not seven days of history — so a genuine 7-day mean isn't something this data source actually supports. Instead we show a short-window estimate, built from the average air temperature across the days the forecast does return, and we label it plainly: an estimate, not a soil sensor reading. For anything precision-dependent — like deciding whether to sow grass seed, where the RHS gives a minimum soil temperature of 7°C — a cheap soil thermometer pushed 50mm into the ground beats any forecast-based estimate.
Frequently Asked Questions
What does "estimated frost risk" mean, and is it the same as an official Met Office frost warning?
No. It is our own algorithmic estimate, calculated from the forecast overnight minimum, humidity, wind and cloud cover — not an official Met Office warning. Always check the Met Office directly when safety matters. Our estimate is designed to help with everyday decisions, like whether to fleece tender plants tonight, and uses cautious language ("frost likely", not "frost certain").
How is the estimated frost risk calculated?
We combine the forecast overnight minimum temperature with humidity (to estimate dew point using the standard Magnus-Tetens meteorological formula), wind speed and cloud cover. Clear skies and calm wind both raise radiative frost risk, because heat escapes to a clear night sky fastest when nothing traps it. The result is a category — None, Low, Moderate or High — and thresholds are set cautiously so a borderline night rounds up.
How accurate is a 5-day forecast for gardening decisions?
Short-range forecasts (1-3 days) are generally reliable for frost-relevant conditions, because the key ingredients — clear skies, light wind, low humidity — are usually visible in the data several days out. Day 4-5 forecasts carry more uncertainty. For anything you'd be upset to lose to frost, re-check the forecast on the day before deciding whether to leave plants uncovered.
What is the soil temperature estimate, and how reliable is it?
It's an estimate only, based on the average air temperature across the short window of days this forecast actually returns — not a direct soil sensor reading. Soil responds more slowly than air temperature. For anything precision-dependent, such as grass seed germination (RHS minimum: 7°C), a cheap soil thermometer beats any forecast-based estimate.
Why don't you show a 7-day soil temperature average?
Because the Met Office daily forecast we use only returns one past day plus a handful of forecast days, not seven days of historical air temperature — so a genuine 7-day rolling mean isn't something this data source can honestly support. We show a short-window estimate instead, labelled plainly as an estimate.
Does rain in the forecast change the frost risk?
Indirectly. Rain usually comes with cloud cover, and cloud cover reduces radiative frost risk because it traps outgoing heat near the ground overnight. A clear, calm, dry night is the classic recipe for a hard frost; an overcast or breezy night is much less likely to produce one, even at a similar daytime temperature.
Should I use this forecast instead of the Frost Date Calculator?
Use both, for different jobs. The
Frost Date Calculator gives you historical typical and "safe in nine years out of ten" dates for planning your season months ahead. This page gives you a live, short-range read on the next five days — useful for deciding whether to fleece plants tonight or hold off planting this week.
What happens if the live forecast is unavailable?
If the live Met Office data can't be reached, the page shows a clear "forecast temporarily unavailable" message rather than a blank or broken page, with a link back to the Frost Date Calculator for general seasonal guidance.
GardenCalc