Rising temperatures and a new round of storms are turning deep mountain snow into runoff just as fresh rain soaks already saturated ground. Together, those forces are pushing rivers, creeks, and storm drains toward capacity in several vulnerable regions, from Southern California canyons to low-lying communities along the Great Lakes. Flood warnings are climbing not because of a single extreme event, but because snowmelt, prolonged rainfall, and fragile infrastructure are lining up in ways that leave little room for error.
As I track these systems, a common pattern emerges: intense winter storms stack up, snow piles high in the hills, then a warmer, wetter phase arrives and squeezes that stored water out all at once. When that happens over burn scars, coastal bluffs, or flat urban neighborhoods with aging drainage, the risk of flash flooding and river flooding rises quickly. The latest alerts from city officials, meteorologists, and emergency managers show how that risk is playing out on the ground right now.
Storm sequence sets the stage in Southern California
Across Southern California, a sequence of winter storms has already soaked the region, setting up a dangerous backdrop for any additional rain. Earlier this month, a powerful winter storm system brought heavy rain, mountain snow, strong winds, and isolated thunderstorms across California, with impacts stretching from coastal counties to the Sierra Nevada, according to The Latest. Another system then followed, flooding many Westside streets as a second in a series of storms swept through, and a flood watch remained in effect for much of the coastal plain as daily rainfall records fell in some coastal ranges, as described in a report that highlighted how a flood watch remains in place.
Those back-to-back systems did more than create short-term street flooding. They primed hillsides and river channels for trouble as additional moisture arrives on a snowpack that is already significant in the higher elevations. A national forecast described a dramatic winter shift that brought snow and flood risks across the United States, noting that Denver experienced clouds and mountain snow while other regions faced heavy rain. In California, that same pattern means that as snow accumulates in the mountains, valleys and coastal zones are seeing repeated downpours that leave soils saturated and waterways running high.
Los Angeles County under prolonged flood watch
Within that broader pattern, Los Angeles County has become a focal point for concern. A regional forecast earlier this week highlighted how flood watches and advisories are in effect for more than 16 million people across Southern California, including Flood watches and for Los Angeles, Santa Barbara, and Ventura counties. That same outlook warned that some areas are very sensitive to heavy rainfall, which I interpret as a reference to burn scars, steep canyons, and densely built urban corridors. Local coverage has described how officials issue flood watch and flash flood alerts for Los Angeles County because heavy rain, mudslides, and debris flows are possible when intense bands of precipitation move over those vulnerable slopes, as summarized in a report that listed Key Points about the current storm…