The weather in California is a rollercoaster, and this April is no exception. With record-breaking temperatures and precipitation, it's a far cry from the usual springtime weather. The state has experienced a bizarre water year, starting with record rainfall in October-December, followed by a scorching March, and now a return to damp conditions in April. The Sierra Nevada snowpack remains in a virtual dead heat with 2015 for the lowest on record, despite the recent precipitation. The Upper Colorado River basin snowpack is also at an all-time low for this time of year.
This week, a 'bowling ball' low-pressure system will bring another round of widespread precipitation, scattered thunderstorms, and late-season Sierra snowfall. While it's not as dramatic as the previous system, it will still be impressive for the time of year. The secondary wave of precipitation on Tuesday will likely trigger lines of convective showers and isolated thunderstorms, with a possibility of severe thunderstorms in the Central Valley. Snow levels will start high and crash as colder air moves in, leading to significant accumulations above 6,000 feet.
The unusually active April pattern may continue into late April or early May, with lesser precipitation events scattered across most model ensemble members. The subtropical jet stream is also playing a role, driving a sequence of events in the subtropical central and eastern Pacific, from Kona Lows in Hawaii to record-shattering rainfall and contributing to ridge-building during the exceptional March heat episode. This pattern could persist into early May, supporting occasional showers later into the spring than usual in California.
The Pacific Ocean is also experiencing a marine heatwave, with record-breaking sea surface temperatures in the subtropical Pacific region between Hawaii, the Pacific Coast of Mexico, and central/southern California. This warmth will have a significant impact on California and the broader Southwestern climate in the weeks and months to come. I expect a muted 'May Gray/June Gloom' marine layer season, with warmer temperatures driven by elevated overnight warmth and occasional humid heatwaves. Later in the summer, there's a chance of elevated convective activity along the western fringe of the typical monsoon region, with a higher risk of tropical remnant events and East Pacific hurricanes.
In conclusion, California's weather is a complex and ever-changing affair, with a mix of record-breaking temperatures, precipitation, and oceanic warmth. The state is in for a unique spring and summer, with potential impacts on the climate and weather patterns that could last for months.
