Racecast verification: Rolex 24 Hours of Daytona

By Doug Schneider

It's time to take a look back and see how well I did with the forecasts for the Rolex 24 Hours of Daytona. 

If you're not familiar with how forecasts are verified in the spreadsheet below, here's a quick summary - the two top rows show the temperatures and precipitation that was observed at the Daytona airport, just behind the Speedway backstretch. The rows below that show the forecast temperature and PoP (Probability of Precipitation) each day that I made a new forecast. The columns with the dates are for each day and night period during the event, Thursday through Sunday. Day is defined as 7 am to 7 pm. The colors in the boxes show how far off my forecast was from what was observed, with the color legend at the bottom. 

Thursday's forecast had some low rain chances mentioned, and while there was some rain observed, it came during the evening, around 9 pm. Since the rain and clouds arrived a little later, temperatures warmed more than I expected from my initial forecast, but at least the updates trended in the right direction.

​Friday through Saturday stayed dry, with temperatures getting much cooler behind a front. I was happy to get the temperatures right both days and even into Sunday. 

Saturday night and Sunday was, well, a mixed bag. It looked like the race would stay dry when I did my initial forecast, but soon after that, some of the models started to change their tune. There continued to be quite a bit of disagreement in the models right up to Friday, and the model that had been showing the most rain (the GFS) was bouncing back and forth between a lot of rain and almost no rain from one model run to the next. With the forecast update on Thursday, it started to look more like there would be some light rain or sprinkles, but much of the rain would evaporate before it hit the ground due to dry low level air. The rain started to look more significant with Friday's forecast update, and I mentioned amounts between a tenth and a quarter inch. On Saturday morning, the timing of rain starting to fall looked to be around midnight, but drops began to be reported at the track around 9 pm. Watching on TV and reading reports on Twitter from fans at the track, it seemed like there was a lot more rain than was actually recorded - the airport measured 0.18, and the rain gauge at the track recorded 0.16. But it was enough to cause an extended caution period. I think my impact level of Low understated the impact that the rain had on the race, but the forecast rain amounts were spot on. My race day forecast on Saturday had rain ending between 9 am and noon, followed by some breaks in the clouds by the end of the race, which were accurate.

So Saturday night and Sunday were a bit of a struggle at first,

but it turned out alright in the end.