Mushroom Weather

Data, thresholds and sources.

Mushroom Weather makes fairly specific claims: rain from days ago, soil moisture, elevation shifting a season. Here is exactly where those numbers come from, and where the tool's judgment starts.

Data sources

What we read.

• Open-Meteo forecast API: no key, free. We request 14 days of past weather and 7 days of forecast: daily precipitation and temperature, hourly soil moisture at 0-7 cm depth, and elevation, all from a single call.
• Open-Meteo geocoding: no key, used when you search a place by name.
• BigDataCloud reverse geocoding: no key, used only to show a readable place name when you use your own location.
• Nothing is stored. Your location is used for that one call and discarded.

The rain lag

Why yesterday's rain does not count yet.

Fungi fruit days after a rain heavy enough to trigger them, not the morning after. So the rain that enters the score is the total that fell 4 to 12 days ago, the trigger window. Rain from today and the three days before is shown in the chart but does not enter the score yet: it starts counting once it reaches the window.

Thresholds

How the numbers become a verdict.

Each reading earns points, and each label next to a number on the page comes from the same points. The most a place can score is 8.

• Rain 4 to 12 days ago: up to 6 mm almost none, 0 points; over 6 mm light, 1; over 15 mm good, 2; over 30 mm plenty, 3.
• Soil moisture, 0-7 cm: under 15% dry, 0 points; from 15% slightly moist, 1; from 22% moist, 2; from 30% very moist, 3.
• Temperature: 8 to 20°C favourable, 2 points; 4 to 25°C borderline, 1; outside that unfavourable, 0.
• Verdict: 6 points or more, prime conditions; from 4 to 5, worth a look only when more than 6 mm of rain fell in the 4-to-12-day window; otherwise, too dry. The sentence under the verdict names the reading that helps most and the one holding things back.
• Last rain: the most recent run of consecutive days with at least 1 mm each, within the last 14 days.
• Best day: for each of the next 7 days we slide the 4 to 12 day window forward and score it again, using the forecast temperature of that day. The highest score wins. If every day scores the same, we say that no day stands out instead of picking one.

Season bands

Latitude and elevation, not a calendar.

The season is worked out from latitude, elevation and the date, all free from the same weather call, never from the country you are in. Out of season the page gives no weather verdict, only how long until the next window. These are our own heuristics, not an official biological standard:

• Temperate (40-55°): main flush 25 August to 20 November, spring flush 20 April to 10 June.
• Mediterranean (25-40°): about two weeks later than temperate, with the main flush 10 September to 15 December, spring flush 10 May to 20 June.
• Boreal (above 55°): about two weeks earlier and shorter, with the main flush 10 August to 25 October, spring flush 21 May to 30 June.
• Tropical (below 25°): no calendar season at all. The verdict depends only on rain, soil and temperature.
• Negative latitude: southern hemisphere, every window shifts by six months.
• Elevation: above 200 m, the autumn window moves about four days earlier for every 300 m of climb; the spring window moves about six days later per 300 m, since snow melts later going up.

Limitations

What this is not.

• This is a heuristic we built, not a peer-reviewed forecasting model. Treat it as an educated guess, not a guarantee.
• It knows nothing about local soil type, forest composition, slope, sun exposure or wind. Two spots 10 km apart can behave differently for reasons this tool cannot see.
• It counts how much rain fell each day, not how it fell: it cannot tell a short downpour from steady rain with the same total.
• For the days ahead it reuses today's soil moisture: it does not forecast how fast the ground will dry out.
• It says whether a walk is worth trying. It says nothing about what you find, whether it is safe to touch or eat, or the rules where you are. Learn your species, and check local regulations yourself.
• Weather data comes from Open-Meteo's models, which carry their own forecast uncertainty, especially further into the 7-day window.

Last reviewed: September 2026.