During the last decade Global Positioning System (GPS) Continuous Operating Reference Stations networks have become a new important data source for meteorology. This has dramatically improved the ability to remotely sense the atmosphere under the influence of severe mesoscale and synoptic systems. The zenith tropospheric delay (ZTD) is one of the atmospheric variables continuously observed, and its horizontal variations, the horizontal tropospheric gradients, are routinely computed nowadays within the dual‐frequency GPS processing, but their interpretation and relationship with the weather is still an open question. The purpose of this paper is to contribute in this direction by studying the effect that Hurricane Harvey had on the spatial and temporal behavior of the ZTDs and gradients, when it reached Texas coast, during 18–31 August 2017. The results show that ZTD time series present a clear and rapid increase larger than 10 cm in a few hours when the hurricane reached the area. Gradients behaviors show that the hurricane also produced significant changes on them, since the magnitude and predominant directions before and after the hurricane arrived are completely different. Noticeably, the gradient vectors before the landing are consistently related to the horizontal winds and pressure fields. In this manuscript we demonstrate that the ZTD gradients can show a consistent signature under severe weather events, strongly suggesting their potential application for short‐term weather forecasting.

The series of 16 Climate Outlook Forums' (COFs') seasonal precipitation forecasts for southeast South America since December 1997 are verified. The COFs' forecasts consist of a probabilistic tercile distribution of precipitation for the upcoming 3 months period, over a domain in South America between 20 and 40°S, to the east of the Andes Mountains. The COFs' forecast is the result of the consensus agreement between atmosphere model predictions, physically based statistical model predictions, results of diagnostic analysis and published research on climate variability over the region, and expert interpretation of this information in the context of the current situation. The validation is conducted by means of the hit score (HS), which expresses the percentage of forecasts verified in the dominant predicted category, and the ranked probability skill Score (RPSS), which measures the difference between the probability distribution of the forecasts and the observed categories. The HS reveals that over most of the region the categorical agreement is low and close to 33%, which is the result that would be obtained by a three-category random forecast, and only sparse regions achieve a categorical agreement between 40 and 50%. The regions with positive RPSS (i.e. forecasts better than climatology and potentially useful for applications) represent 30% of the total area considered by the COFs. There are significantly large regions with negative RPSS, i.e. forecasts worse than climatology. The result of the COFs' forecasts is compared with that of the IRI Net Assessment forecasts, the only source of physically based seasonal forecasts regularly available at the COFs' discussions. There is general coincidence in the regions with positive and negative skill. Although one might expect the consensus of the COFs' forecasts to improve upon the skill of the IRI forecast, this was not the case during this period.

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