By Doug Schneider

No big changes to the forecast for IMSA weekend at WeatherTech Raceway Laguna Seca. Overall, the weather will be very nice for racing, with mostly sunny skies each afternoon and pleasant temperatures.

Expect clouds to spread in overnight, and linger into the morning each day. This is due to a northwest wind that will persist all weekend, bringing in a marine layer of moisture, resulting in low clouds forming overnight. The clouds should lift around the late morning and early afternoon.  

By Doug Schneider

Nice weather is expected for the IMSA weekend at WeatherTech Raceway Laguna Seca. Through this week, high pressure will be drifting east across California, eventually settling over the Rockies by the weekend as a weak trough moves into the west coast. This trough will bring cooling temperatures over the weekend, and maybe some high clouds. Overall, skies will be mostly sunny. As is typical for the Monterey Peninsula, moring fog may develop. At this time, it is too early to forecast fog with any confidence. With a west wind off the ocean, fog will be possible, but I will wait until we get closer to the weekend to add it to the forecast.

By Doug Schneider

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The forecast for Le Mans has been really tough this year, as the models have been flip-flopping regarding the timing of a low pressure system that will cross northern France and England. The good news is that they seem to be coming into better agreement, and showing better consistency. The most likely time period for showers at the track appears to be from late afternoon on Saturday into the evening. There could still be some light showers or sprinkles that continue overnight and into Sunday morning, but those should be light. Bottom line, I think the biggest potential impacts from rain could be around the start of the race. Temperatures will be on the cool side due to the extensive cloud cover from this system and behind it on Saturday and Sunday. 

by Doug Schneider

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The models have taken a pretty big shift over the past few days, and are now showing a good chance of rain during the race.

The days leading up to the race should have good weather for practice, qualifying, and support races. Temperatures will be comfortable for Wednesday through Friday, gradually climbing from the lower to mid 70s F to lower 80s F, under partly cloudy skies each day. 

There is agreement among the models that a low pressure system will track from the northern Atlantic to the English Channel over the weekend. This should bring a chance of rain to Le Mans starting late Saturday afternoon. The system will be slow-moving, so the chance of rain will continue Saturday night and Sunday. At this time, it is nearly impossible to pin down the timing more precisely than that. Timing should become more clear later in the week. Temperatures should be warm at the start of the race Saturday afternoon, then become cooler on Sunday behind a cold front.

By Doug Schneider

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The weather for Le Mans looks great this year. A few showers are possible on Thursday, and while the race day is still a week away, it appears that the weather pattern will favor a dry race. 

Temperatures are very hot right now across France as a large high pressure system is in control of the weather. But that will change in a few days as a cold front is expected to cross northern France on Monday, followed by cooler temperatures. Behind the front on Wednesday, expect mostly cloudy skies and highs in the mid 70s F, or mid 20s C. 

Models differ on the chance of rain for Thursday. Some show a completely dry day, while other show a disturbance in the mid and upper levels crossing northern France. I think there is enough of a chance of the later scenario that I needed to include a small chance of showers on Thursday. But the impact looks small if showers do occur, as it is a weak and fast-moving trough. 

A ridge of high pressure is expected to build over the western Atlantic on Friday, and continue to build east into Spain and France over the weekend. It will provide dry conditions and warming temperatures, with highs peaking on Sunday in the upper 80s F, or lower 30s C. 

I'll be away for a few days, so my next planned update will be on Tuesday. 

By Scott Martin

Sorry for the delay in getting a forecast discussion out to you for the IMSA Sportscar Weekend at Road America. Unfortunately, the forecast for the fans at the track may be wet at times, as the weather pattern shows the potential for showers and thunderstorms to pass through at times throughout the weekend.

A surface low is located due north from the track over the Great Lakes that will slowly move eastward today, bringing with it a cold front that will move into the northern half of Wisconsin. Showers and storms will be possible early through the morning hours, with chances increasing during the main heating of the day for the afternoon hours, then decreasing chances when we reach the late afternoon to early evening hours. While it will not rain the entire time, rain could occur at any time. Otherwise, skies will be partly to mostly cloudy today, with highs reaching the lower 80s. The overall rain chance is 60%. Winds will be out of the southwest at 5-15 mph.

The cold front will continue to hang out over the middle of Wisconsin on Saturday, but the good news is that the weather will not be all that bad. We'll only have a small chance of a few showers or storms during the afternoon to early evening hours, only around 30%. Skies will be partly to mostly cloudy, with highs around 80 degrees. Winds will be out of the east at 5-10 mph.

Rain chances will rise once again on Sunday as another surface low will approach the area from the west and will stay west of the state, but it will pull more moisture up into the state. The cold front will be over the southern parts of Wisconsin, but it will start to push northward again as a warm front. Showers and storms will be possible throughout the day, but the greatest risk will be during the mid to late afternoon hours. Skies will be partly to mostly cloudy, with highs reaching the lower 80s. Winds will be out of the south at 5-15 mph, with the potential for gusts of 25 mph during the mid to late afternoon. Overall rain chances will max out at 50%.

By Doug Schneider

The main change to the forecast for IMSA's Northeast Grand Prix at Lime Rock Park is a higher chance of rain on Saturday. 

The weather pattern on Friday will have a low pressure system moving east across the Great Lakes region, with high pressure off the East Coast. This will make Friday a fairly typical summer day, with scattered afternoon showers popping up as instability increases, and high temperatures in the mid to upper 80s. The chance of rain at the track is only 30%, but the expected timing in the mid to late afternoon could affect the qualifying sessions. 

As the low pressure system tracks from the Great Lakes to western New York, moisture will increase over Connecticut. On Saturday afternoon, instability from daytime heating and lift ahead of the trough will make showers and thunderstorms likely. The most likely time for rain to start is near or after 2 pm, so the WeatherTech race is the most likely race to see impacts. Lightning and a brief heavy downpour will be possible, which could temporarily stop the race. 

Follow @RacecastWx on Twitter for weather and radar updates on Saturday. 

By Doug Schneider

The weather at Lime Rock Park at the end of this week will be a fairly typical one for mid-July. A large high pressure system will be located off the Mid-Atlantic coast, which will produce a southwesterly flow across New England. Warm and humid conditions can be expected on Friday and Saturday, with a chance of afternoon showers and thunderstorms both days. At this time, it looks like the chance will be higher on Saturday, due to a trough of low pressure that starts to approach the area from the northwest. There are differences in how the models handle this trough and how quickly it moves toward Connecticut, and this will affect the rain chances on Saturday. The 40% chance is a middle-of-the-road approach, so it could change as we get closer to the event. High temperatures both days will be in the mid to upper 80s, with a little more cloud cover expected on Saturday than Friday.