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Racecast verification: 25 Hours of Thunderhill

12/8/2014

Comments

 
by Doug Schneider (@Race4caster)
Any meteorologist who takes his job seriously will check his forecast against what actually happened. Experience is the best teacher. Verification is how we learn what went wrong, what went well, and how we can do better. Scott and I want to be open about our forecasts, and show you how we're doing. At regular intervals through the race season, we'll post a summary of how our forecasts have verified.

A few points of note: PoP is probability of precipitation, or the percent chance of rain that is forecast. For more on what that means, see this post. Since most race tracks don't have any weather instrumentation that is publicly available, we have to use the nearest available weather station, usually a nearby airport. This is the "verification point", named by its three-letter identifier. In this case, SAC NWR is a weather station located about 15 miles SE of Thunderhill Raceway. There may be times when the observations at the verification point differ from the track, but the difference should not be significant most of the time. We verify precipitation based only on if measurable rain fell at the observation site, and not based on how much rain fell. Thus, the "observed precip" row will either be Yes or No. 

The rainfall forecast was pretty much right on the money for the 25 Hours of Thunderhill. I had the chance of rain in the right time periods with my initial forecast, and I correctly raised the PoP forecast for Friday night as it approached. In a tweet, I said rain would begin to move in between 4 and 6 pm, and it began around 5:30 pm. 0.17 inches of rain was recorded, which was a little below the range that I had forecast in a tweet (0.25-0.5). The entire race was dry, as I had forecast from the beginning.

The temperature forecast was good each day, but off at night. Temperatures did not drop nearly as much as I expected. Probably my biggest forecast error, and one that does not show up in this spreadsheet, was wind. Observed wind speeds on Friday were 10-15 mph, and 15-20 mph with gusts to 25 mph Friday night. I had forecast 5-10 mph winds during these periods. The higher-than-expected winds may explain why the low temperature forecasts were off. Higher winds at night create more mixing of the air near the surface, which prevents cold air from settling at the ground.

Since rain is probably the most important part of the forecast to most people at a race, I'm pleased with how my forecast verified.
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Forecast update: 25 Hours of Thunderhill

12/3/2014

Comments

 
by Doug Schneider (@Race4caster)
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Rain chances will be increasing through the day on Friday, and there could be some light rain around for qualifying Friday afternoon. Rain is likely by Friday night, with about 0.25 to 0.5 inches of rain expected overnight. Most of the rain should end early Saturday morning, but there could be a little that lingers past sunrise. However, I'm confident that it will end in time for the start of the race at 11 AM. The rest of the 25 Hours looks dry, with some periods of clouds now and then.
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NASA 25 Hours of Thunderhill forecast

12/1/2014

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by Doug Schneider (@Race4caster)
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The week leading up to the NASA 25 Hours of Thunderhill will be very wet, but it is expected that the rain will end in time for the race on Saturday and Sunday. Practice sessions on Thursday are likely to see some rain, and there's a good chance of seeing rain on Friday for qualifying. The timing of rain should come into better focus over the next few days. The upper level trough that is responsible for the rain will exit Friday night, which should leave nice weather for the entire race.
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    Authors

    Doug Schneider, Scott Martin, and Stephen McCoy are race fans and meteorologists dedicated to providing accurate forecasts and timely weather updates at racing venues around the world. We forecast for IndyCar, Indy Lights, Pro Mazda, USF2000, IMSA, Blancpain World Challenge America, and World Endurance Championship, as well as major SCCA and NASA events.


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