Svenesis.orgHow good was the forecast?
The astro weather says every night whether it is worth it. This page checks up on it: for every night of the past weeks it puts side by side what the forecast said one to five days ahead, what the model analysis says in hindsight, and what the nearby airports actually reported. Same colour scale as over there: the deeper the blue, the clearer the sky.
📖 Only the cloud cover can be replayed – per lead time the archive carries neither the inputs for seeing nor the aerosol. That matters less than it sounds: in the overall rating of the astro weather, cloud decides almost everything anyway. Back to the forecast →
The airport reports sit in a university archive that hands out one station at a time, which is why they only come on request.
How to read the chart
One column is one night, named after the evening it starts on. The mean runs over astronomical darkness, each hour weighted by how much of it is dark – exactly how the astro weather forms its night average.
The rows from top to bottom are the lead times: what was forecast five, four, three, two and one day before the night. Below them the two references: the analysis of the finest model in hindsight, and the airport report.
The model column on the left names, per lead time, the model that delivered it. That is not the same everywhere: short-range models such as HRRR or ICON-D2 reach only about a day, after which the next coarser model of the chain takes over. The forecast page worked by that rule too – though since 21 September it lets go of HRRR after 30 hours. The 1 day before row still shows HRRR here, because that very comparison is what prompted the change, and it is where you can watch whether it helped.
The deviation row at the bottom shows, per night, how far the one-day forecast was out: green means close, red means far.
Weather data by Open-Meteo.com (CC BY 4.0) · forecast archive: Open-Meteo previous runs · cloud reports: Iowa Environmental Mesonet, METARs of the airports named. The evaluation is derived from these data.