Conditions throughout the event weekend are beginning to look a little better as overall rain chances have dropped for the actual race, but Thursday's testing sessions will be pretty wet. Rainfall totals throughout the morning and early afternoon hours could total up to or just over 0.25 inches. Winds will be shifting throughout the day starting off out of the southeast at 5-10 MPH but will end up out of the west-northwest at 2-8 MPH by the end of the day. Today's high will top out in the mid-50s and will drop into the upper 40s by the time the paddock closes at midnight. Chance of rain throughout much of the day will be around 90% but will drop to around 30% after 3:00 pm.

Much of the on-track activity will be dry on Friday, but rain chances creep back into the forecast after 3:00 pm, which could affect the qualifying sessions. The good news is that the rainfall appears to be light but may be just enough to bring out the rain tyres. It will be partly cloudy throughout the day and the afternoon high will be in the mid-50s. Rain chances are nearly 0% through much of the day, but increases to 30% after 3:00 pm.

The good news for the main event, The USAF NASA 25 Hours of Thunderhill, should be dry for at least 21 out of the 25 hours. A few light showers may dampen the track during the morning and into the early afternoon hours on Saturday, but those rain chances will only be around 30%. After 3:00 pm, the remainder of the race will be dry, but temperatures will be very cool to pretty chilly. Saturday's high will be in the lower 50s, then falling into the mid-30s for the early morning low on Sunday morning, before warming back into the upper 40s by the checkered flag.

I'll have radar up and running before 10:00 am PST today.

Thursday looks to be a pretty grey and possibly wet throughout the day. Rain will be likely during the morning and much of the afternoon, but those rain chances drop of for the late afternoon through the evening hours while skies become partly cloudy. Temperatures will be in the lower 50s at 7:00 am, warming into the upper 50s for the daytime high, then dropping into the lower 40s at midnight. Rain chances will be around 80% for the morning and into the early afternoon hours, then dropping to around 30% for the remainder of the on-track activity. Winds will start off out of the southeast at 10-20 MPH but will shift out of the northwest by late afternoon at 5-10 MPH.

Friday looks a little better than Thursday, but we'll continue to have a small chance of showers throughout the day. Skies will be partly to mostly cloudy with temperatures at 9:30 am in the upper 40s, topping out in the mid-50s for the afternoon high, and dropping into the lower 50s by the end of the qualifying session at 5:45pm. Rain chances will be around 20% for much of the on-track activity, but increasing to near 40% before the end of qualifying. Winds will be out of the south at 5-10 MPH.

Mostly cloudy skies and a small chance of showers will continue throughout the day on Saturday as the race is scheduled to start just after 11:00 am. Rain chances will be around 30% from the pre-grid at 9:30 am through mid-afternoon, then drops off a little to around 20% for the rest of the afternoon through midnight. Temperatures at the green flag will be in the lower 50s, topping out in the upper 50s for the high, then dropping into the mid-40s by midnight. Winds will be out of the south to southeast at 5-10 MPH.

While we should be mainly dry with partly cloudy skies during the early morning hours on Sunday through the checkered flag at noon and the awards ceremony to follow up during the afternoon, there still remains a very small chance of showers (less than 20%). Temperatures will remain dropping from the mid-40s at midnight to the lower 40s by 3:00 am, but they will begin to climb steadily into the lower 50s by 12:00 pm. Winds will be out of the northwest at 2-8 MPH.

By Doug Schneider

Rain is still on track to affect the Six Hours of Shanghai. The time period when the greatest rain is expected to occur is in the late morning through early afternoon hours, between 10 am and 2 pm. The rain may be heavy enough during that time to cause some delays to the race. After that time, the rain should tend to become lighter. The total amount of rain expected through the race is about a half inch (13 mm). 

By: Stephen McCoy

No major changes in the forecast for this weekend's race at Circuit of the Americas, though the models are still showing a wide range of temperatures for the high on Sunday. Confidence is not high for the temperature as a result of the model spread. In addition, timing of the high is uncertain, but looks increasingly like it will occur in the morning due to the cold front moving in and dropping temperatures for the rest of the day.

The SREF plumes ensemble spread shows a mean temperature around 50F on Sunday, though with very low confidence as not a single member matches the mean line.

The 06Z and 12Z GFS model runs (blue lines) show a spike in temperatures on Sunday as the model shows the front passing in the afternoon, allowing temperatures to warm from daytime heating. However, the 06Z and 12Z runs of the NAM (red lines) show the front passing in the morning, with cold air moving in from the north behind the front. Daytime heating still occurs in the NAM runs, but the effect occurs hours after the front has passed.

By Doug Schneider