By Doug Schneider

There's no good news to report today about the weather forecast at Thunderhill Raceway this weekend. A deep and slow-moving low pressure system will be crossing Northern California, bringing periods of rain and breezy conditions from Thursday night through Saturday night. The only change change to the forecast worth mentioning is that the models are showing this system moving slightly slower than before, and to account for that, I have added a chance of rain to Sunday morning. So while the vast majority of the 25 Hours will be run in the rain, the final stages of the race, possibly the final 3-6 hours, may be rain-free. Through the event, I expect that rainfall amounts will likely be between 1 and 2 inches. Wind will also be a factor on Friday and Saturday, with sustained winds from the south to southeast at 15 to 25 mph, with gusts between 30 and 40 mph at times. 

By Doug Schneider

I wish I could bring better news of a dry and sunny forecast for the 25 Hours of Thunderhill, but unfortunately, it looks like it will be a very wet weekend in Willows, California. 

A strong low pressure system will be tracking west across the Pacific through the week, and arrive in northern California just in time for the on-track action. As teams set up and start to practice on Thursday, clouds will be increasing but most of the day will remain dry, with just a slight chance of rain possible late in the day. The chance of rain will be increasing Thursday night, and by Friday there will be periods of on/off rain as a flow of deep moisture spreads into the area ahead of the low pressure system. This system will be slow-moving, so rain will continue to spread across the area through Friday night and Saturday. There will also be a good southerly breeze on Friday and Saturday, with sustained winds between 15 and 25 mph, with higher gusts. The total amount of rainfall through Saturday could be between 1 and 2 inches. However, it's still a long way out in the forecast, so the forecast rain amounts will come into better focus as we get closer to the weekend.

Rain is expected to start tapering off on Saturday night. This far out, timing is uncertain, but right now I expect that by daybreak Sunday morning, all the rain should be gone. Clouds will start to decrease as drier air moves in, and there may be a mix of sun and clouds by the checkered flag. 

Check back for updates to the forecast through the week.

By: Stephen McCoy

Springtime conditions are in full swing in South Africa this weekend for the Kyalami 9 Hours. The race weekend will kick off with some lingering showers possible during the early morning on Thursday after showers and thunderstorms are present on Wednesday as an upper level trough moves eastward over the region. As upper level winds return to zonal flow, an area of high pressure is expected to build in at the surface, diminishing chances for precipitation during the remainder of Thursday; some moisture will remain in the lower levels, causing partly to mostly cloudy conditions.

Conditions will wane overnight with mostly clear skies anticipated for Friday morning. Warming air temperatures and dew point temperatures near 16°C (60°F) will allow CAPE values in the afternoon to approach 1000 J/kg, providing an environment for possible thunderstorm development. Similar conditions are likely for Sunday, and may bring a chance for isolated showers in the early afternoon once again.

By Doug Schneider

There has been a pretty big shift in the forecast for Sunday at VIR, and it now appears that there will be a good chance of seeing rain during the day. 

A cold front is expected to move into the area Saturday night, which is in line with the previous forecast thinking. However, the models are now showing this front slowing down and stalling as it moves into the Piedmont of NC and VA. It is expected to be located just southeast of VIR on Sunday. Meanwhile, an upper level disturbance will be approaching, and its interaction with this front will produce some showers in the area. Rain is possible any time of the day on Sunday, but it appears that the best chance of rain will come in the afternoon. Rain amounts in the neighborhood of a tenth of an inch can be expected. Since this isn't expected to be a heavy rainfall, and no lightning is expected, I kept the impact as low.

By: Stephen McCoy

A cold front moving through the region on Saturday will bring more cloudy conditions than the rest of the weekend, with slightly cooler temperatures. Surface winds are expected from the west to southwest during the morning, but will shift to the west to northwest behind the front. Temperatures will be about the same as the previous few days, but will cool behind the front; temps by the end of the race will be in the low to mid 60's. There is a slight chance for isolated showers ahead of the front near the early to mid afternoon; model output suggests maximum totals during the race around a few hundredths of an inch should precipitation occur.