May 2, 2018 – Isolated showers over the northern Sierra today, otherwise drier and warmer through the end of the week. A slight cooling next week with a chance of light showers at times mainly over the mountains.
Discussion
Northern California currently under upper level northerly flow between upper low over southern California and a building high pressure ridge over the eastern Pacific. A shortwave disturbance rotating around the top of the low brought scattered showers and isolated thunderstorms to the northern Sierra last evening. These showers have since dissipated overnight and the CWA is under mainly fair skies this morning. Another such shortwave may bring a few showers to the Sierra this afternoon and evening but otherwise the forecast area will be under fair skies and warmer temperatures. Slightly warmer temperatures are expected Thursday and Friday as the upper ridge axis slides inland. Models displace upper ridge eastward and inland enough by Saturday to allow an upper low over the Pacific to start impacting the north state. Saturday will see increasing cloud cover and possibly a slight cooling. Isolated showers will be possible over the coast range by evening with enough instability indicated for a slight thunderstorm threat as well.
Extended discussion (Sunday through Wednesday)
Ridge of high pressure shifts east as a series of disturbances move across northern California for the start of the extended forecast period, which will bring chances for mountain showers. Warm temperatures through next week will range between five and ten degrees above average.