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.

By: Stephen McCoy

Warm and pleasant conditions will welcome the WeatherTech SportsCar Championship series for its season finale at Road Atlanta this weekend. The main thing of note in this forecast is the possibility of a cold front moving into the region on Saturday that could bring a slight chance for isolated showers, though at this point the models are subjective as to the location of the front.

Conditions for Wednesday, Thursday, and Friday are very similar in terms of the overall atmospheric set-up. A surface high pressure system will move into the Midwest region behind a cold front on Tuesday. The anticyclonic rotation around the system will cause winds over the Southeast to be largely from the east to northeast, slightly amplified by a possible tropical cyclone in the Atlantic. An upper level ridge will keep the surface system fairly stationary over the following days, finally relegating its influence over the region Friday into Saturday. Cloud cover on Friday may be slightly higher than earlier in the week as low level winds bring moisture from the Atlantic to the area as they are directed more from the east.

Meanwhile, an upper level trough is expected to move eastwards across the US and allow a surface low pressure system to develop on the eastern side of the Rockies around mid-week. The deepening of the trough will force the system towards the Midwest Thursday into Friday with a cold front extending southwards into the Gulf of Mexico. The trough is anticipated to move over the surface low, causing it to stall over the Midwest Friday night into Saturday. However, the cold front from the system will continue to move eastward, approaching Georgia sometime during the day. The models at this point are split on when a frontal passage may occur. An earlier passage will bring a slight chance for showers during the morning and a cooler afternoon high temperature while a later passage would allow temperatures closer to those seen earlier in the week and precipitation further towards the evening. The front would also change wind direction, coming mainly from the south ahead of the front and shifting to the west to northwest behind the front. With the amount of subjectivity to the forecast this far out, it will likely change in the coming updates during the week.

By Doug Schneider

Not much has changed in the forecast for WeatherTech Raceway Laguna Seca this weekend. No rain is expected through the event, with temperatures starting off warm on Friday but getting cooler each day. The one change to the forecast is to bring in more cloud cover on Sunday, associated with the upper level trough that will be approaching the area. It does not appear that there will be enough moisture for rain, just some partial cloud cover. This trough will also help cool temperatures to the lower to mid 70s on Sunday. It should be a great weekend for racing.

By Doug Schneider

Beautiful California weather is expected this weekend as IMSA visits WeatherTech Raceway Laguna Seca. Sunny skies are expected each day, with pleasant temperatures. There will be a cooling trend each day, with Friday reaching the mid 80s, cooling to highs in the mid 70s on Sunday. This is due to an upper level trough that will be approaching, although it won't have enough moisture to produce rain, or even clouds. 

One thing to watch for as we get closer to the weekend will be morning fog or low clouds. Fog can be pretty common at Laguna Seca if the wind direction and ocean-land temperature difference are right. At this time I think it is unlikely to have any impact, so I'm keeping it out of the forecast.

By Doug Schneider

There are no major changes to the forecast for Portland this weekend, as it still looks like the weather will be nice for racing each day. There is a small chance of seeing some light sprinkles in the area on Sunday, but it should not have an impact. 

The main weather feature to affect Portland will be a low pressure system moving slowly across the Pacific toward the Northwest coastline. This will push a front through the Portland area on Saturday night. Most of the rain with this front will stay offshore or just near the coast, and rain will decrease as it moves inland. Still, there may be some sprinkles that reach Portland on Saturday night and Sunday. I don't think there would be enough rain to even measure a hundredth of an inch, if it happens at all. The front will also cause a wind shift from south of Friday and Saturday to west on Sunday.