Cloud Properties of Cold Fronts Affecting Central Chile: Low and High Freezing Level Storms

This study analyzes the cloud properties associated with cold fronts that affected central Chile during May-September 1998-2014 using observational and reanalysis data. Warmer, moister, and more unstable conditions in early winter favor the development of deeper mixed-phased clouds in cold fronts, having larger rain and ice water contents. Late in the season, cooler, drier, and more stable conditions predominate, favoring the development of a larger percentage of shallower warm-phased clouds. Years when cold fronts show large environmental humidity and high cloud tops were associated with stronger systems that produced the largest precipitation. The linear positive relationship between cloud tops and precipitable water reported in the Central and Eastern Pacific was also found in storms developing in the Eastern South Pacific. The intensity of cold fronts also determines their cloud development and observed rainfall. High freezing level (FL) cold fronts are more frequent in May and June, generally occur in very high humidity environments, are stronger, include more rain and ice water contents, and allow the development of the highest clouds compared to low FL storms, which are more frequent in August. The strength of low FL storms, instead of their available humidity seems to be the key factor controlling the rain they produce. On the other hand, the intensity of high FL storms seems not to be a decisive factor in controlling its rainfall. Finally, the presence of an atmospheric river seems not to guarantee the rainiest events among high and low FL cold fronts.