Forty years of weather, thanks to NASA
Behind every “warmer than normal” in FairGrow sits NASA POWER: four decades of satellite-based weather for every place on Earth, free for anyone to use. We use it to tell you whether this month is normal for your field, and as a second opinion on the weather you see.
The record behind the comparison
A single week of weather tells you what happened. Only a long record tells you whether it was unusual. We did not collect forty years of weather for your field. NASA did, for the whole planet, and publishes it without a key, a licence or a fee.
NASA Langley Research Center, the POWER project
POWER stands for Prediction Of Worldwide Energy Resources. It began as a service for solar energy engineers and grew into a climate record for farmers, builders and researchers. The POWER team at NASA Langley in Hampton, Virginia, has been maintaining it since the 1990s.
The numbers do not come from weather stations. They come from MERRA-2NASAModern-Era Retrospective analysisA reanalysis: a weather model run backwards over the past, corrected hour by hour with every satellite and ground measurement NASA could find. The result is a consistent record for every point on Earth, even where no station has ever stood., NASA’s reanalysis of the global atmosphere since 1980, and from the CERES and FLASHFlux satellite instruments that measure how much sunlight reaches the ground. Together they give temperature, humidity, wind, rain, soil wetness and solar radiation on a grid of roughly fifty kilometres, hour by hour, since 2001, and monthly back to 1981.
Two things make POWER special for a grower. It covers every plot of land on Earth with the same method, so a garden in Armenia gets the same quality of record as a field in the Netherlands. And it is entirely independent of the weather models that make your forecast, which is exactly why we use it as a second opinion.
Acknowledgement: data obtained from the NASA Langley Research Center POWER Project, funded through the NASA Earth Science/Applied Science Program. Shown under every block that uses it.
Two questions, nothing more
NASA POWER can answer hundreds of questions. FairGrow asks two, because two is what a grower needs from a forty-year record.
What is normal here, per month?
Twelve monthly normals for sunlight, temperature and rainfall, averaged over decades. This is the yardstick. Without it, “18 degrees in May” is just a number. With it, it becomes “two degrees above what May usually brings here”.
What did the last week look like?
Hour by hour for the past seven days: temperature, humidity, wind, sunlight and the moisture in the topsoil and the root zone. From those we compute ET₀Water balanceReference evapotranspirationHow much water a short, well-watered grass surface would lose to the air in a day, in millimetres. It is the standard yardstick for crop water demand. FairGrow computes it from temperature, humidity, wind and sunlight, so two independent sources of those give two independent ET₀ values., the water your crop is losing to the air.
The forecast
POWER looks back, not forward. Your forecast comes from the weather models behind Open-Meteo. That separation is deliberate: the record that judges the forecast should not come from the same place as the forecast.
Where NASA shows up
Three places. In none of them do you have to know what a reanalysis is.
Seasonal climate in Location context
A climate diagram of your spot with the temperature and rainfall normal for every month, and one sentence about now: sun and warmth above or below what the season usually brings, and what that means for water demand.
Second opinion in the weather layer
Switch NASA on next to Open-Meteo in the temperature, humidity, wind, soil moisture and ET₀ charts. The shaded band shows how far the two disagree. When they agree, trust the number; when they part ways, be careful with it.
Wet bulb in the spray window
The spray window depends on the difference between air temperature and wet bulb temperature. Both sources give their own wet bulb, so you see whether the window is solid or just one model’s opinion.
Two sources, one band
Open-Meteo runs a forecast model that is nudged towards reality every few hours. NASA POWER rebuilds the past from satellites and a reanalysis, about a day later. Neither is the truth. The distance between them is honest information, and we show it instead of hiding it.
Asking politely, storing carefully
NASA serves this record to the whole world for free. We treat it the way a good guest treats a host.
A normal does not change
Forty-year averages move very slowly, so we ask for them once every ninety days per location and keep the answer. Two growers within a few hundred metres share one set.
The last week, half an hour at a time
The hourly record is kept for thirty minutes before we ask again. Opening the same chart ten times costs NASA one request, not ten.
Your coordinates, not a neighbour’s
A POWER cell is fifty kilometres wide. We ask for the normal at your own coordinates, not at the rounded point a forecast model returns, because the neighbouring cell can be a mountain with a June normal ten degrees colder than your valley.
Honest about the lag
A reanalysis needs a day to catch up with reality. The newest hours arrive as blanks, and the chart says how old the newest real value is instead of drawing a line where there is none.
No key, no account, no tracking
POWER asks for nothing in return. We send only a latitude, a longitude and the names of the variables we need. Nothing about you travels to NASA.
Quiet when NASA is quiet
If the service does not answer, we wait before asking again, and your dashboard simply shows the other source. A missing second opinion is shown as missing, not invented.
No licence, and a thank you anyway
NASA data is produced by the United States government and carries no copyright and no licence. Anyone may use it for anything. The POWER team asks only that users say where the data came from, so that the programme that funds it can see what it made possible.
We think that is a small price for forty years of weather, so the acknowledgement appears under every block that uses it and in every report that includes a seasonal comparison. The same goes for SoilGrids, the ISRIC soil map shown next to the climate normal in your location context, and for the Copernicus satellites that see your field from space.
NASA POWER is one of several open sources in your dashboard. The forecast comes from the weather models behind Open-Meteo, history and air quality from the Copernicus climate and atmosphere services, pollen from SILAM, satellite images from Copernicus Sentinel-2, the soil baseline from SoilGrids and field boundaries from the European farm registers. Your own sensors sit in the middle of all of it.
See how normal your season is
Create your account and add your location. The forty-year normal for your spot appears in the location context, and the second opinion is one switch away in every weather chart.
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