Here is a sample of the weather patterns & forecasts central Chile & Argentina, where the next year’s total eclipse will occur (July 2nd). Let’s simply imagine what if it would be this year if he had a 24/48/72 hours forecast.
Update: Comparison with real satellite images from July 1-3 is added.
One should understand that this year’s doesn’t have to be the same as the next year, and usually the weather is largely unpredictable until the last 1-2 days. By then we’ll be in a nearby location anyway. Yet having a plan and knowing the typical forces driving the local climate never hurts a successful eclipse chaser!
July 1st afternoon (24h forecast).
It appears that the model underestimates the low clouds above the Argentinian pampas (although it shows a rough trend), while exaggerates the amount those on the Pacific coast. On the other hand, the model is precise on large systems – rain/snow in Chile. Another pinch of salt will be the jet stream, which produces Lenticular clouds over the Andes and spreads long patches of Cirrus to the east. This dynamic phenomenon seems to be another week side of the model.
Day’s conclusion: It would be still a good choice to stay in San Juan and an observation would’ve been successful on this day. Although the reliability of the forecast in other places is questionable.
July 2nd afternoon (48h forecast)
The model keeps doing the same big error with underestimating the extent of low clouds across the pampas. This would be crucial for the most of San Juan and La Rioja provinces this day. Only the high-altitude valleys of Calingasta and Pismanta is protected
from by the Precordillera range – BUT – here comes another problem. The jet stream forms a lot of Cirrus/Lenticular clouds that would’ve spoiled the view on this day.
Day’s conclusion: One of the fewer bad days in Argentina.
July 3rd afternoon (72h forecast)
It only gets worse and colder… Although there are many days with sunny clear skies across the continent, days like this July 3rd exist, when everything looks bad. Pacific fog, snowfalls in the Andes, moist cloudy weather across the pampas.
Day’s conclusion: Chile got lucky again despite the risky forecast. Another bad day across all of Argentina – that clear gap west of La Plata could also disappear within some hours.
Sounds all to bad?
Well, fortunately not. Last week turned out to be a cold spell in the region with excessive cloudy weather. On the adjacent days the situation was very different, here are a few examples:
Over the last 10 years the weather on 2nd of July was predominantly perfect, with exception for 2012 and 2016. Even those ‘bad’ years, Valle de Pismanta had some clear skies. Judge by yourself: