A haze which has hung over Singapore in recent days is continuing to cause concern ahead of the race weekend.

Despite the notoriety of its weather, many have commented on the fact that not once in its seven year history has the Singapore Grand Prix, the sport's only true night race, been affected by rain.

As we revealed back in 2013, this is largely down to cloud seeding, a principle first discovered in 1946 by Vincent Schaefer.

Over the years the process has been used throughout Asia, in Australia, Europe, North America and Africa. In early 2013 it was used in Indonesia in an attempt to turn clouds into rain before they arrived in Jakarta which was suffering severe flooding which had seen the deaths of 41 people and millions left homeless.

However, whilst the rains might have been held back, or moved on, a haze, the result of forest burning in nearby Indonesia presents an entirely different problem.

Minded of the problems caused over the weekend of the 2010 Chinese Grand Prix by an ash cloud, following the eruption of an Icelandic volcano, some sections of the media have opted to hold back in terms of the possible threat to this weekend's race.

The official Singapore GP website offers little information of worth - though fans are warned that tickets must not be re-sold and drones are strictly prohibited - merely redirecting readers to the National Environment Agency (NEA).

The latest update from the NEW reads: "There was some improvement in the haze conditions this morning (Monday). However the respite was brief as haze from Sumatra was again blown in by the prevailing winds this afternoon. As at 8pm today, the 24-hr PSI was 130-161, in the low to mid sections of the Unhealthy range, and the 1-hr PM2.5 was 181-341 µg/m3.

"Hotspots could not be detected in Sumatra today due to partial satellite pass and cloud cover. Widespread moderate to dense smoke haze was observed in central and southern Sumatra. The haze has spread to the surrounding sea areas.

"For the rest of today and tomorrow, the prevailing winds are forecast to blow from the southwest, and the current hazy conditions are expected to persist. The haze situation could further deteriorate should the current unfavourable winds blow in denser haze from Sumatra. Thundery showers are forecast for Singapore in the pre-dawn and early morning hours, but this may only bring a brief temporary respite to the hazy conditions. The 24-hour PSI for the next 24 hours is expected to be in the mid to high sections of the Unhealthy range, and may enter the low section of the Very Unhealthy range if denser haze from Sumatra is blown in."

Race organisers say they have a "contingency plan" though, as ever, fans are likely to be the last to know. However, to emphasise the seriousness of the threat, many flights in to Singapore have been diverted or cancelled.

As of this morning (Tuesday), Singapore's Straits Times reports that the 24-hour Pollutant Standards Index (PSI) is between 126 and 151. It's worth bearing in mind that the unhealthy range is 101-200.

A number of other events have been cancelled in recent days and schools in Singapore ban outdoor and physical activities when levels of pollution are in the very unhealthy range.

"Given the air quality forecast for the next 24 hours, healthy persons should avoid prolonged or strenuous outdoor physical exertion," advises the NEA. "The elderly, pregnant women and children should minimise outdoor activity, while those with chronic lung or heart disease should avoid outdoor activity. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention."

Previously sessions at events have been delayed when poor visibility meant the medical helicopter couldn't take off.