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Low-flow events can cause significant impacts to river ecosystems and water-use sectors; as such, it is important to understand their variability and drivers. In this study, we characterise the variability and timing of annual total frequency of lowstreamflow days across a range of headwater streams within the continental United States. To quantify this, we use a metric that counts the annual number of lowflow days below a given threshold, defined as the cumulative dry days occurrence (CDO). First, we identify three large clusters of stream gauge locations using a Partitioning Around Medoids (PAM) clustering algorithm. In terms of timing, results reveal that for most clusters, the majority of low-streamflow days occur from the middle of summer until early fall, although several locations in Central and Western United States also experience low-flow days in cold seasons. Further, we aim to identify the regional climate and larger scale drivers for these low-streamflow days.