By: Stephen McCoy

Lots of clouds for raceday at the 24 Hours of Le Mans. Temperatures for the start of the race will be consistent with previous forecasts, being in the upper 60s F, or around 20 C. A surface low pressure system is expected north of the British Isles and will move eastward through the forecast period. A cold front extending into northern France will move through the region during this time, and is the reason for some stronger winds at the start of the race. The front will move out of the region around midnight weakening winds through the night and morning on Sunday. Temperatures at the end of the race will be similar to those at the start.

Below is the astronomical information for the race from timeanddate.com

By: Stephen McCoy

As I mentioned in the previous forecast discussion, a strong surface low pressure system is expected to move through northern Europe, between Scotland and Iceland. As the system tracks eastward, a cold front will extend south from the system, bringing rain and strong winds to Ireland and the United Kingdom Thursday morning. As it progresses during the day, the front will extend to northern France causing some breezy conditions with some stronger wind gusts possible. Once the front exits the region, westerly winds are expected in the lower and upper levels of the atmosphere, in addition to the surface. These winds will bring moisture off the north Atlantic and bring a chance of precipitation into the area during the evening and into Thursday night; there is a possibility that passing showers could impact the qualifying sessions on Thursday.

As a result of showers overnight, some fog is possible in the early morning until sunrise on Friday. Overcast conditions are likely to start the day, but as the day progresses expect much of the cloud cover to break up. With little motion at the surface and lower levels, look for light winds out of the north and northwest.

For Saturday, a low pressure system will move towards Ireland and the United Kingdom from the North Atlantic Ocean during the morning hours. An upper level shortwave trough located over the surface low will help contribute to some slightly stronger winds at the surface during the day. However, as the day progresses, the shortwave trough will propagate east and winds in the upper level will shift towards the north. The surface low will likely weaken as it moves over the British Isles and as a result wind speed will likely weaken as well. With the combination of upper levels winds from the north to northwest, and lighter winds at the surface and lower levels, look for mostly cloudy skies for the majority of the day. Similar conditions are expected on Sunday, as upper level winds are likely to weaken from the shortwave trough continuing its track eastward.

By: Stephen McCoy

For Wednesday, winds in the upper and lower levels of the atmosphere and at the surface are expected out of the north. As the winds are vertically stacked through the atmosphere, some moderate wind gusts are likely. Partly cloudy skies should persist through the day as the winds will bring moisture off the North Atlantic Ocean and the English Channel.

A strong surface low pressure system located between Scotland and Iceland is expected to move towards the northeast past Scandinavia. A strong cold front will be associated with this system and will track over the United Kingdom and could extend into northern France in the early afternoon on Thursday. This will cause winds to shift from the north to the west to southwest, with some stronger gusts likely. With winds primarily out of the west from the North Atlantic Ocean in the upper and lower levels of the atmosphere, and lifting from the cold front, there is a chance of showers into the evening hours and overnight, likely impacting the 2nd and 3rd qualifying sessions for the 24 Hours.

Winds in the atmosphere will continue out of the west, though not as strong as on Thursday; surface winds will be variable through the day. A slight chance of showers is expected in the morning, as the mainly westerly flow will continue to bring moisture off the North Atlantic. As the day progresses, winds in the lower levels will shift towards the southwest. With the addition of daytime heating, precipitation chances will decrease and mostly cloudy skies will be expected for the remainder of the day.

For Saturday, conditions will start partly cloudy with variable winds at the surface and light winds from the west and southwest in the remainder of the atmosphere. As the day progresses, a shortwave trough in the upper atmosphere is expected to move through northern France; this will bring warmer, moist air into the area from the Bay of Biscay. With the addition of low level winds from the west to southwest, a slight chance of showers is expected in the afternoon to evening hours of the race. However, as the trough passes through the region overnight, winds in the upper levels will shift towards the north to northwest and as a result, precipitation chances will decrease into the morning on Sunday; mostly cloudy skies and light winds will persist throughout the remainder of the day.

By: Stephen McCoy

For tonight’s update for the Le Mans test day on Sunday, conditions look to be relatively constant with previous forecasts. Expect partly cloudy conditions in the morning practice session and a low temperature in around 60 F, or the mid-teen’s C. Winds will be out of the east to northeast at 8-12 mph with some stronger gusts approaching 20 mph, or 14-20 kph with gusts at 32 kph.

The afternoon session is where I’d like to put emphasis due to the slight chance of showers in the late afternoon. Initially, the global models were indicating any kind of precipitation for test day, however over the past day the high-resolution regional models have trended more towards the same result. Current model runs are showing precipitation towards the end of practice, around 5:00-6:00pm local time. Because these showers could be scattered through the area, in addition to the timing, I’ve decided to indicate a low likelihood of delay for on track activities.  

By: Stephen McCoy

For the Le Mans test day this Sunday, little has changed in the forecast as far as temperatures for the day; expect a low temperature around 60F, or in the mid-teen’s C, and a high temperature in the upper 70’s to low-80’s F, or the mid-to-upper 20’s C. Where things have changed are in the upper atmosphere. In the previous forecasts, the upper level low has been located off the western coast of Europe in the northern Atlantic Ocean. Because of this, winds were expected from the south or southwest. However, in the latest model runs, a secondary upper level low is expected to move through the Iberian Peninsula on Saturday and into the Mediterranean Sea early Sunday. The low will weaken on Sunday, however with the upper level low in the North Atlantic, the winds in the upper levels are expected to come from the southeast, bringing moisture from the Mediterranean into the region.

The ECMWF and GFS models, which are global forecasting models, both indicate some amount of precipitation towards the late afternoon and early evening hours on Sunday. However, the high-resolution European models are showing the majority of precipitation towards the southwestern portions of France. For the moment, I’m inclined to follow the high-resolution models, as they’re results take into account smaller-scale interactions between the land and atmosphere. Though I am confident for the moment for no precipitation for the test day, look for an updated forecast Saturday night into Sunday morning for a better look at the conditions for the day.

With winds at the surface and lower atmosphere coming from the east to northeast, and now with upper level winds coming from the southeast, expect windier conditions than previously forecast with some stronger gusts in the region.