Will it rain on the 18th? This is the projection just 1 month away from national holidays

According to popular belief, on September 18 it usually rains or drizzles. But according to statistics from the Chilean Meteorological Directorate (DMC), this is not as true as it is believed, and it is not a trend that repeats itself year after year.

At Estación Quinta Normal, for example, between 2007 and 2016 there is no trace of precipitation for September 18, while in 2006 there was barely 1.1 mm precipitation. Considering the days September 18 and 19, In 2000, the biggest eighteen-year rain in the past 20 years occurred, when statistics showed 9mm of rain.

In 2018 light rains were recorded, and in 2017 0.7 mm. In other words, in the past 20 years, it has rained only four times.

In Valparaíso, the situation is similar. It usually does not rain on September 18 and 19. According to data from the same DMC, at the Rodelillo station, the year with the greatest number of precipitations was 2000, when on Wednesday the 19th it received 39.2mm of rain. In 2012, 2.6 mm was recorded, the second highest record in 20 years. Then 2018 with 1.0 mm, 2006 which marked 0.6 mm and 2017 with 0.3 mm. In the past 20 years, it has only rained five times for national holidays.

Climatologists explain that there is always Chance of rain for national holidays, since it is a period of seasonal change (winter-spring), when there is usually precipitation such as hail, rain and electrical activity, caused by mass shocks of air of different characteristics. Statistically the probability that it rains on the dates of National Holidays is 55% .

in the design, Carriel Sur Station, for geographical reasons the rain is more important. Over the past 20 years, it has rained ten times on public holidays. However, the trend is repeated as in Santiago and Valparaíso, the year 2000 was the rainiest, 32.9 mm fell in the capital of the Eighth Region. In 2007, 13.2 mm was recorded, in 2018 the figure reached 12.0 mm, in 2012 11.0 mm and in 2003 7.8 mm, among others.

According to Miguel Fernández, meteorologist and professor at the PUCV School of Marine Sciences, the probability of rain on September 18 is 50%. However, it states that the rain during the month of September is over 70%.

But specify that just about 10 to 15 days before we can go and see what can happen and at 5 days the prognosis is more reliable.

Jorge Carrasco, meteorologist and academic at the University of Magallanes (UMAG) , partly agrees with Fernández and says that the probability of knowing if it will rain is “between 0 and 100%”. From the dynamics of the atmosphere, which atmospheric models try to simulate, there is no way of knowing whether or not it will rain on September 18, he explains.

“Although the models show simulations up to 15 days, they drastically drop their accuracy after day 5. therefore the forecasts between 6 and 10 can give an indication of what could happen, but the occurrence of the event is uncertain. After the tenth day of forecasting, success is even more uncertain,” he adds.

However, he latest quarterly report from the Chilean Meteorological Directorate (DMC) show that the most probable condition for the quarter July, August and September, between the regions of O’Higgins and Magallanes, is the precipitation “above normal” . This would be equivalent to exceeding the 66th percentile of quarterly precipitation.

For example, in Talca more than 254 mm must be recorded, in Concepción more than 435 mm and in Puerto Montt more than 510 mm. Between the Coquimbo region and the metropolitan region, the forecast has a greater degree of uncertainty. Despite this, it indicates a trend towards a “normal” to “above normal” condition. This would imply that the upper threshold of normality is exceeded in Santiago for the 155mm quarter, the report adds.

Despite this, Carrasco says that it must be understood that the seasonal forecast is for the entire quarterly period, it is the sum of the probable precipitation accumulated during the three months due to the occurrence of precipitation events which, this year due to the presence of El Niño is favored. “But in practice, it’s not a prediction to infer how likely it is to rain on the 18th.”

The report also covers minimum and maximum temperatures. The minimums would be below normal in the central area, in the rest of the country above normal, while the maximums would be above normal throughout the country. In general, the days will present a greater thermal amplitude.

This week, in particular, the DMC does not indicate any precipitation in the capital, only partly cloudy skies, with maximums between 15 and 20 degrees, and minimums around 5°C. Other weather portals indicate rain in Santiago.