By Doug Schneider - @Race4caster

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The forecast for the Bathurst 12 Hour hasn't changed much from what I posted on Monday. The weather pattern continues to feature a large high pressure system off the southern coast of Australia that will be drifting slowly toward the east through the weekend. 

I took the small chance of showers out of Friday's forecast, as it appears more likely today that showers will be confined to the Blue Mountains, and stay well east of Bathurst. It will be a really nice day at the track, with highs in the mid 70s F and mid 20s C, with partly cloudy skies. 

Saturday continues to have a chance of afternoon showers, and I've raised the chance of rain to 40% today. The main difference from Friday to Saturday will be a stronger southeasterly flow that will allow showers that develop over the Blue Mountains to track farther west. I think that any showers at the track will be fairly short-lived, producing rain amounts in the range of 2 to 5 mm (0.1 to 0.2 inches). 

If there is rain on Saturday, then fog is likely to form on Sunday morning for the start of the race. It's hard to say how dense the fog will be at this point, and it is possible that there could be some impact on the race start, perhaps a delay until the fog lifts. It's hard to say for sure since that will depend on a shower occurring on Saturday to moisten the ground. The rest of Sunday looks very nice, with mostly sunny skies and a high near 80 F and 27 C - much cooler than last year's race. 

​I'll have at least one more forecast update posted before the start of the race. 

By Doug Schneider

Let's take a look back at how well the forecast for the Rolex 24 verified.

The forecast did well in the most important area - the precipitation forecast. The initial forecast on 1/21 mentioned a few sprinkles or a brief light shower were possible on Saturday night and Sunday morning, which is exactly what occurred. Only a trace of rain was reported at the airport from a small shower around 8 pm that lasted about 10 minutes. That initial forecast was uncertain about the timing of heavy rain, but the two later forecasts mentioned that heavy rain appeared likely to hold off until after the race ended. There were some periods of sprinkles Sunday morning, but heavy rain wasn't reported at the airport until 6:50 pm. I'm very pleased with how the forecast worked out. 

The low temperature forecast didn't work out as well on Thursday night and Friday night, but I don't think anyone will be too critical for missing the overnight temperatures that were warmer than forecast. I suspect the reason that temperatures stayed so mild overnight was that the wind each night stayed up, between 8 and 14 mph. Calm winds allow for the temperatures to drop lower than when winds stay up. The low temperature forecast Saturday night during the race was good, which was probably the most important night to get right.

There was more sunshine on Sunday than I expected, which allowed temperatures to rise to 77 degrees that afternoon, about 4 to 5 degrees higher than forecast.

By Doug Schneider - @Race4caster

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The Bathurst 12 Hour is one of my favorite races of the year, and one reason is that it's a rare chance for me to do a forecast in the Southern Hemisphere. It's a little different since winds around low and high pressure system circulate in the opposite direction from the Northern Hemisphere, so a south wind brings colder air and a north wind brings warmer air. 

The general pattern for late this week across Australia will be a high pressure system off the southern coast, near the Great Australian Bight, and west of Tasmania. It will remain fairly stationary through the weekend, but slight changes in the flow across New South Wales and its flow over the Blue Mountains will bring varying rain chances at Mount Panorama each day.

On Friday there will be southeasterly flow off the Tasman Sea into New South Wales. As moist air off the ocean hits the Blue Mountains, plus some afternoon heating, some showers will develop. I expect that the showers will stay mainly over the higher terrain of the mountains, and are not likely to move far enough west to reach Bathurst. Still, I did put a very low chance of a shower in for Friday afternoon because I can't completely rule it out at this point. 

On Saturday, the flow turns to a slightly more southerly direction, and gets a little stronger. Showers will probably develop over the Blue Mountains again in the late morning to early afternoon, but with the stronger flow, they are more likely to reach Bathurst on Saturday than on Friday. So I have a higher chance of rain on Saturday afternoon.

On Sunday the high pressure ridge drifts a little closer to New South Wales, and this should have the effect of weakening the southeast winds. With weaker winds running over the Blue Mountains, there is less of a chance that showers will develop, so I have a dry forecast for Sunday.

Temperatures at last year's race were quite hot, but that shouldn't be a problem this year, thanks to the southeasterly winds. Temperatures will be quite pleasant each day, with highs in the mid to upper 70s (mid 20s C) on Friday and Saturday, and near 80 (27 C) on Sunday.

Check back through the week for updates, and be sure to follow our social media feeds, which you can find on the top of the sidebar.

By Doug Schneider - @Race4caster

A look at radar this morning (see the Radar link at the top of the page for our live feed) shows a few light showers off the east coast of Florida, moving toward the northwest. Through the day, it is possible that some sprinkles will be felt at the track. But it is likely that there won't be enough rain to even measure, less than a hundredth of an inch. The east to southeast wind off the ocean will persist through the night, and keep cloudy skies over the track overnight. It should also help keep temperatures fairly mild, as low temperatures will stay above 60 degrees tonight.

As the sun rises over Daytona Sunday morning, there could be a few more spits of rain, but they are unlikely to have any impact on the racing. In the afternoon, there is a better chance of getting more rain, however I still expect that before the race ends, the amount of rain will be less than a tenth of an inch. It may require a change to wet tires in the closing stages of the race, or perhaps create some difficult strategy calls for teams deciding if they need to make the change to wet tires. The overall impact of any rain on the race will be low, as I don't expect it to be heavy enough to warrant any delays or interruptions.

The timing of heavier showers today looks a little slower than the past few days, which is good news. I think that any chance of thunderstorms or heavier rain will hold off until after 4 pm. From 4 pm to sunset, around a quarter to a half inch of rain may be possible. But I'm feeling pretty confident that the heavier showers and storms will hold off until after the race has ended.

Scott and I will be tag teaming with weather updates through the race at our main Twitter feed - @RacecastWx.

By Doug Schneider - @Race4caster

The past few days have been a challenge to figure out the timing and amount of rain that can be expected on Sunday. Fortunately, my confidence in Sunday's forecast is higher as the models are coming into better agreement today. 

For Friday and Saturday, the forecast hasn't changed much. Friday will start off mostly sunny, but clouds will be increasing through the day. There will probably be more sun than clouds from Friday afternoon through Saturday due to an easterly wind off the ocean. This moisture will be shallow enough that I don't think there will be any rain, at least not until Saturday night. I can't rule out a few sprinkles on Saturday night, but it expect that it would not have an impact on the race. 

With Tuesday's update, I showed how two models were showing very different rainfall amounts between 10 am and 4 pm. Here are the same two models, from today's morning run, with their prediction for rainfall in the same period of time:

The one on the left (GFS) has Daytona in the 0.12 to 0.2 range, and the one on the right (ECMWF) has Daytona in the 0.04 to 0.08 range. This is much closer than what they were showing on Tuesday, and fortunately, the wetter model on Tuesday (GFS) has become much drier. That gives me confidence that the race, which ends at 2:40 pm, will avoid heavy rain or storms that will cause delays or a stoppage.

Here's an animation of another model, the NAM, and its depiction of rainfall between 7 am and 7 pm (each time step is three hours apart - 7 am, 10 am, 1 pm, 4 pm, and 7 pm):

This shows the arrival of light rain at Daytona between 10 am and 1 pm, with between 0.1 and 0.2 inches of rain falling between 10 am and 4 pm. This is right in line with the amount that the other two models above are showing.

So here's what I'm thinking today about what to expect on Sunday - there may be a few sprinkles early in the morning, but not enough to have any significant impact. Light rain showers (more than just sprinkles) are likely to arrive at the track in the mid to late morning, starting between 9 am and noon. Light on/off showers will continue from noon until the end of the race, with the rain getting heavier after the race ends, probably between 3 pm and 6 pm. The amount of rain from the time it starts to the end of the race will likely be between 0.05 and 0.15 inches. If that happens as expected, then the rain tires should be able to handle it, and I don't foresee the race having to be stopped. 

There is still 72 hours and several more model runs before we get to Sunday afternoon, so this could change completely before then. But that's what I'm thinking right now. I'll have another update on Saturday at the latest.

By Doug Schneider

I did not need to make too many changes to the forecast today, as the forecast I posted on Sunday is still generally on track. I made a few small changes to temperatures, mainly to go slightly cooler on Thursday and for the morning low temperatures. I also raised the chance of rain on Sunday a little as the models continue to show a cold front moving through the area during the afternoon. 

The big question remains the timing of rain, which isn't much clearer today than it was on Sunday. Remember when I said that one model was faster to bring rain into Daytona, and another was slower? Well, the two models have completely flipped with each other - the faster one slowed down and the slower one sped up. As an example of what I'm dealing with between these models, here are their depictions of how much rain will fall between 10 am and 4 pm Sunday:

The GFS model on the left has around 1.5 inches at Daytona in that six hour period. Obviously, that would have a major impact on the race. On the right, we have the European (or ECMWF) model, which only has about 0.05 inches of rain at Daytona, with the heavier rain staying to the west until the evening. 

So as you can see, there's still a lot of uncertainty about the timing of rain and how much rain will fall before the end of the race at 2:40 pm. 

I still think the most likely scenario is scattered light rain showers around the track late Saturday night through Sunday morning (maybe a few hundredths of an inch), with heavier and more numerous showers, and perhaps a thunderstorm, arriving in the afternoon. Whether that will happen before or after 2:40 pm, I can't tell this far out. The science of meteorology isn't that exact. But if you are heading to the race, it's always a good idea to be prepared for wet conditions. 

I plan on having the next update posted on Thursday, unless there's a big change before then.

By Doug Schneider

It's almost time to go racing! I know everyone is hoping for great weather at Daytona this weekend, and the forecast has some good aspects (warm temperatures!), but some bad as well (chance of rain on Sunday). 

A cold front will be passing through Daytona on Tuesday, which will bring a chance of showers as teams start to load into the track and setup in the paddock area. By the time on-track activity begins on Wednesday, this rain will be gone but temperatures will be cooler as high pressure builds in, with highs in the 60s and lows in the 40s. 

The high pressure system will be moving across the Southeast states through Thursday, then move off the coast on Friday. As this happens, winds will shift from a northerly direction to an easterly direction on Friday, then southeasterly on Saturday. The result of this will be a warming trend each day, but also increasing clouds each day as moisture starts to increase. 

On Saturday, a low pressure system will be moving across the central United States, with a trailing cold front moving across the Gulf Coast region. The front will move across the Florida Panhandle on Saturday night, then into the Florida Peninsula on Sunday. There is good agreement between the models that showers and some thunderstorms will occur ahead of the cold front, but there are some differences in their timing. And for the race, timing is everything. On the bright side, and nice southerly wind will provide comfortable temperatures in the 70s on Saturday and Sunday, so there won't be a cold rain like last year.

We are still too far away from Sunday to pin down the timing with any certainty, but I think the most likely scenario right now is that there may be some light rain showers Saturday night and Sunday morning, with an increasing chance of rain through the day. In the afternoon, there may be some heavier showers with some thunderstorms possible. The end of the race is at 2:40 pm EST, and I cannot say with any confidence whether the heavier rain will come before or after the end of the race. We'll just have to wait and see how things develop through the week before I can give more detail on the timing.

​Stay tuned to our social media feeds on the right to keep up with the latest forecast updates.

By Doug Schneider

The Rolex 24 is just two weeks away, which is within range of the extended weather models. A lot can change in the forecast over two weeks, so I'm not going to make a detailed forecast this far out. But I'm getting excited about the start of the racing season, so I thought I'd share what I'm seeing in the weather pattern for the race weekend (I did a Twitter thread on this topic this morning on our @RacecastWx account).

Here are a couple images that summarize the pattern for the Rolex 24 weekend. These images are taken from the GFS model, valid Friday 1/26. They are temperature and moisture (precipitable water) anomalies, which means how much the model is expecting temperatures and moisture content to depart from normal. Normal temperatures at Daytona for Rolex 24 weekend are a high of 69 and a low of 48. 

There is a high pressure ridge located off the east coast that provides a southerly flow across the eastern portions of the U.S., with a low pressure system tracking across the Ohio Valley region and a trailing front down to the Gulf Coast. Because of that pattern, this model is predicting above normal temperatures across Florida (in the range of 3-6 degrees above normal), and slightly above normal moisture content. 

If this general pattern holds true, I am pretty confident that temperatures will be warmer than normal for the Rolex 24. I am less confident about the chances of rain. Just because the moisture is above normal does not necessarily equal rain, as there are other factors in play that are too uncertain this far out.

Check back here the week before the race for the detailed forecast, and be sure to follow @RacecastWx on Twitter, as it will be our main social media feed for all of our posts (and more) this year.