At launch time Tuesday (1330Z 7/18) it looks to be overcast at FL100. There are major differences between the GFS model and the higher resolution ECMWF. The ECMWF predicts more rain and more clouds at low levels than the GFS. While the GFS forecasts < 1mm precipitation and only thin low clouds during the flight time, the ECMWF has 1-2 mm precipitation and scattered clouds below FL100, increasing toward late afternoon. Both models forecast winds backing with height until becoming westerly above FL100. Wind speeds ranging from 50 kts at FL100 to 80 kts at FL 300.
The high resolution WRF model has light precipitation west of El Calafate, but not much there. Note the the WRF is based on GFS initialization so it is not surprising it would go with less precip in El Calafate. Vertical cross sections show moderate lift over the mountains to about FL260 and moderate to strong lift (1000–1500 fpm) farther east above FL700, but little to no connection between the two.