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 Doug Schneider

The weather pattern across eastern China this weekend will be a wet one that will not change much from one day to the next, which means that rain will be a factor in the racing each day.

A front is expected to stall near the Shanghai area on Thursday. Moist air spreading from south to north will run up and over this front. A steady rain will start on Thursday night and continue through Friday. The upper level flow will be from west to east, parallel to the front, so the front will not move much over the weekend. It may drift slightly south, but that should have little impact on the weather, as rain will likely continue into Saturday, and probably into Sunday. One positive aspect of this forecast is that the rain does not appear to be heavy. I expect it will be a steady, persistent light rain that will produce about a quarter to half an inch  (6 to 13 mm) each day. As a result, I have a Low impact each day, meaning that rain tires will be needed and there may be some delays to the action, but I do not expect the rain to be heavy enough to cause cancellations. 

That's how the forecast looks today, and I plan to have the next update posted on Wednesday, unless there is a big change in the models before then.

By: Stephen McCoy

Overcast conditions are likely to dominate the forecast for Saturday at the Six Hours of Fuji as moisture from the southwest out of the East China Sea. Temperatures will be cooler than initially forecast around 50F(10C) as surface winds moving over the Sea of Japan enter the region from the northeast. A surface low pressure system mentioned in previous forecasts is still expected to form to the south of Japan during the day on Saturday. Rain likely overnight Saturday as the system approaches the southern coast; moisture from the Pacific will wrap around the east side of the system, bringing moderate to heavy rainfall at times. Due to the timing of the approach of the low pressure, there's a medium chance for track activities to be impacted, especially activities towards the end of the day.

For Sunday, precipitation from the low pressure system is likely to continue through the morning with lower chances for scattered showers throughout the day. With chances extending through the day, there is still a low impact for the early part of the race. With more zonal flow in the upper levels, drier air will move in, with a slight decrease in cloud cover, though conditions are likely to remain mostly cloudy. Daytime heating mixed with the source of the surface winds coming from the low pressure system will allow temperatures to warm closer to 60F(15C).

By: Stephen McCoy

Cool conditions remain in the forecast for the Six Hours of Fuji, however the higher chances of precipitation have shifted more to Friday and Saturday night into Sunday morning.

The pattern in the upper levels looks to stay relatively consistent with the previous forecast with a longwave trough moving through on Friday with a shortwave trough following close behind, and conditions returning to a more zonal flow on Sunday. At the surface, the cold front from a low pressure system to the north is expected to linger in the area on Friday, with a chance for rain concentrated in the morning and possibly early afternoon. Due to high pressure to the east, winds will be from the east to northeast, though with a slightly stronger pressure gradient winds will be around 5-10 mph (8-16 kph).

An area of low pressure is expected to form to the south of Japan, ahead of the shortwave trough, and could bring a slight chance of showers to the region Saturday afternoon or evening. The system is expected to track to the northwest, approaching the southern coast overnight Saturday into Sunday morning before turning east towards the North Pacific Ocean. There is a likely chance of rain during this time frame, with chances decreasing as the day progresses. Winds will continue from the northeast as winds wrap cyclonically around the low.

High amounts of relative humidity in the low levels will keep conditions mostly cloudy to overcast for most of the forecast period. A shift in low level winds to the north on Sunday afternoon is expected to erode some of the cloud cover into the evening hours.

By: Stephen McCoy

A cool and wet weekend looks in store for the Six Hours of Fuji this weekend with temperatures hovering around 60 degrees Fahrenheit (15.5 degrees Celsius) each day.

An upper level longwave trough currently centered over eastern Mongolia and northeastern China will persist over the region in the coming week. Towards the end of the week, the trough will deepen slightly, extending southwestward as the trough itself moves east. Much of Japan will be downstream of the center of the trough, resulting in upper level winds being primarily from the southwest for the first part of the weekend. With winds from the southwest, moisture will move into the area in the upper levels from the East China Sea and the Philippine Sea. As the longwave trough moves past Japan on Friday, a shortwave trough is expected to develop behind the longwave trough and to the west of Japan. This shortwave trough will pass over early Sunday morning, where conditions will return to more zonal flow with upper level winds from the west.

The aforementioned longwave trough will cause a surface low pressure system to develop over the Korean peninsula and the Sea of Japan around mid-week. As the trough moves eastward, the surface low is expected to move northeast towards the Sea of Okhotsk and eventually the North Pacific Ocean and an area of high pressure is expected to build in. With the high to the west of Japan and the low to the northeast, the area where the two systems meet will cause winds to propagate from the north to northwest, bringing cooler temperatures from northeast China and parts of Siberia. As the surface high continues to build in towards Japan, the winds are expected to shift more to the northeast during the day on Friday. These winds will bring moisture from the Sea of Japan to the region, resulting in a high chance for precipitation during the day.

On Saturday, a surface low pressure system could develop to the south of Japan ahead of the shortwave trough before moving eastward out to the Pacific Ocean. Depending on the location in relation to the southern coast, the system could bring more precipitation to the region as moisture would wrap around the low from the south and east. Should the low pressure system, winds would increase slightly, though they would continue from the northeast due to the area between the two systems being located over the region.

On Sunday, the return to zonal flow will result in upper level winds bringing drier air from the mainland. Moist air in the lower levels will cause some mostly cloudy to overcast skies throughout the day, but with drier air aloft, the chance of precipitation is minimal. With winds continuing from the north to northeast, temperatures will remain cool through the day.