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

By: Stephen McCoy

Slightly below-average temperatures are in the forecast for the 24 Hours of COTA, with sunny and breezy conditions on Friday giving way to more cloudy and windier conditions on Saturday and Sunday. Timing of  a cold front passage on Sunday could determine if temperatures remain in the 60's F or drop to the lower 50's F for the day.

A strong upper level shortwave trough will move through the region towards the southeast US through the beginning of the week into Thursday. A surface low pressure system is expected to develop over the Gulf Coast ahead of the trough, moving northeast up the Atlantic coast late Thursday; an area of high pressure will build at the surface as the low move out of the region. Behind the upper level trough, conditions will return to zonal flow, with winds coming from due west through the end of the week.

Sunny conditions are expected on Friday with dry air moving in to the region at all levels of the atmosphere. Initial surface winds from the southwest will contribute to a low temperature in the mid 40's F, however as the day progresses, winds will shift towards the south as the surface high pressure system slowly tracks eastward across Louisiana and Mississippi. The winds will bring warmer air from the Gulf to central Texas, resulting in high temperatures in the mid 60's F.

Similar conditions are expected on Saturday, with the exception of clear skies, as the zonal flow in the upper levels will bring moisture originating over the Pacific into the area. Conditions will likely start clear in the morning, but cloud cover will increase through the day as the upper level moisture moves over around mid-day. Surface winds will shift slightly during the day to the southeast, causing temperatures to be slightly warmer in the upper 60's F.

Going back to Wednesday, a surface low pressure system will develop over Canada (known as an "Alberta Clipper") and track eastwards through the week. After approaching the Great Lakes region on Saturday, a cold front will extend from the system well to the southwest, reaching into Oklahoma and northern Texas. As the low continues its track, the cold front will track southward, approaching central Texas by Sunday morning. There is currently a split in the models as to when the front will reach the region, with the ECMWF indicating a passage in the early morning before sunrise and the GFS indicating a passage closer to mid-day.

This graphic follows the synoptic pattern provided by the GFS where southeasterly winds from Saturday continue to bring warmer temperatures into Sunday morning before the frontal passage. The result would be a low temperature about 10 degrees warmer than Friday and Saturday. The high temperature would only be a few degrees warmer than the low as the front would only allow daytime heating to occur for a couple of hours before it passes and drops temperatures into the lower 50's F. If the Euro is correct, temperatures will be cooler than on this graphic with the high temperature occurring just after sunrise before dropping to the lower 50's F for the remainder of the day. Regardless of timing of the frontal passage, winds will shift to the north, with wind speeds around 10-15 mph and gusts approaching 25 mph. The front will also bring overcast conditions to the region for most of the day.

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.