By: Stephen McCoy - @stephenmmcc

There are a few changes in this update to the forecast for the next two days at Sonoma Raceway. Some higher wind speeds are looking likely in the afternoon for both Saturday and Sunday as a result of a stronger pressure gradient at the surface. The slightly cooler temperatures seen for Saturday's high and Sunday's low are likely caused by these stronger winds as the cooler air moves into the region from the Pacific.

By: Stephen McCoy - @stephenmmcc

Clear conditions with warm temperatures continue to dominate the forecast for the Indycar Grand Prix of Sonoma at Sonoma Raceway. High temperatures for the weekend are expected to stabilize around the mid-to-upper 70's and with dew point temperatures in the upper 40's to low 50's, heat index values should remain close to the actual temperature. Some moisture in the upper levels could bring some light cloud cover to the region in the late afternoon to evening on Friday, but otherwise conditions will remain clear. Expect maximum wind speed of 5-10mph from the west to southwest each day.

By: Stephen McCoy - @stephenmmcc

A picture-perfect weekend is in store for Indycar for the season finale this weekend at Sonoma Raceway. The eastern edge of an upper level trough will be over the region through early next week with winds primarily from the southwest during this period. The winds will bring mostly dry air to the region during the weekend aside from the later hours on Friday, where some more moisture will cause light cloud cover into the evening and nighttime hours. Surface winds will be around 5-10 mph each day, generally from the west, but they could fluctuate between the northwest and southwest. With plenty of sunshine, temperatures will reach the mid to upper 70's each day, with dew point temperatures in the upper 40's to low 50's, keeping the heat index close to the air temperature.

On Sunday, some fog looks to be possible as saturated air at the surface will be present under a temperature inversion and dry air aloft, but it will erode into the late morning with clear conditions returning for the race.

By: Stephen McCoy - @stephenmmcc

Expect more sunshine and cool temperatures for the rest of the weekend at Portland International Raceway. Winds from the north to northwest will continue in much of the atmosphere, bringing dry air from Alaska and western Canada to the region. Moisture in the lower levels from the Pacific ocean will cause some partly cloudy conditions in the morning and early afternoon, but are expected to lessen as the day progresses. In recent runs, the models have trended towards cooler temperatures on Saturday, with the afternoon high only reaching the low 70's. As I've stated in the previous forecasts, the air at the surface will be dry enough to not have an effect on the heat index, with values nearly identical to the air temperature.

On Sunday, dry air is expected to move in at the lower levels, in addition to the rest of the atmosphere. The result should be mostly sunny conditions, with a few light clouds. The lack of cloud cover will allow for daytime heating to warm the air at the surface, raising the temperature to the mid 70's. Surface winds are expected to be similar to the rest of the weekend, however some wind gusts around 15 mph are possible into the afternoon.

By: Stephen McCoy - @stephenmmcc

Plenty of sunshine and comfortable temperatures remain in the forecast for Indycar's return to Portland International Raceway for the Grand Prix of Portland.

On Friday, the backside of an upper level longwave trough will be over the Pacific northwest, causing winds to carry dry air to the region from the northwest from western Canada and Alaska. Winds in the low to mid levels of the atmosphere are expected out of the west to northwest, bringing slightly more moist air from the Pacific ocean to northwestern Oregon. With dry air aloft and slightly moist air in the mid to low levels, partly cloudy conditions are likely for Friday, with cloud cover decreasing into the evening hours. Surface winds from the north to northwest will keep conditions relatively cool and dry with high temperatures reaching the low to mid 70's. With dew point temperatures around 50 degrees, the apparent temperature will be about equal to the actual temperature.

Similar conditions are expected for Saturday, though with drier air moving into the region in the low levels, mostly sunny conditions are expected with some light cloud cover possible, mostly concentrated in the lower levels. Winds at the surface will remain from the north to northwest around 5-10mph, but with the addition of low level winds also from the north to northwest, there is a potential for gusts around 12-15mph.

On Sunday, the jet stream in the mid and upper levels will be located over Washington and southern Canada and will continue to bring dry air to the region. Mostly sunny conditions will be likely as, in addition to the upper and mid levels, dry air is likely to move into the region at the low levels from the north to northwest. With little cloud cover, daytime heating will warm the surface, with temperatures likely reaching the mid to upper 70's. Again, with low dew point temperatures, apparent temperatures will likely be equal to the air temperatures.