May 3, 2019 – Dry today. Chance of northern Sierra showers Saturday then more widespread, mainly mountain showers Sunday. Sierra showers possible through the remainder of the week, otherwise dry. Above normal daytime temperatures becoming much warmer than normal by the end of the week.
Discussion
Dry with fair skies today under weak upper ridging over the west coast. Daytime highs today are forecast to come in a few to several days above normal for this time of year. Models have been fairly consistent in moving a low, now centered near 33N 139W, coastward on Saturday. For the most part, Saturday looks dry but there may be enough instability and upper level diffluent flow for a threat of isolated showers or thunderstorms over the northern Sierra.
Models move this low on to the central California coast on Sunday. Overall airmass will not see that much cooling but cloud cover associated with the low will bring some cooling most areas especially over the southern CWA closest to the low center. Much of this area south of about Marysville will see a threat of showers with the higher elevations seeing a threat of isolated thunderstorms as well. Some NorCal mountains will see a chance of showers on Sunday too but the lower elevations north of Marysville currently look dry. The upper low is forecast to move very slowly into southern California on Monday. Northerly flow behind the low should bring an end to the shower threat for much of the forecast area but the shower threat over the Sierra Cascade range will continue going into early next week. Temperatures remain down some on Monday but still above season normals.
Extended Discussion (Tuesday through Friday)
Ensembles continue to be in reasonable agreement with the overall pattern featuring an upper low/trough lingering over the southwest states. Thus, showers are possible over higher terrain next week; best chances over the Sierra. Temperatures might be near or slightly above average across the southern portions of the region, but less cooling is expected across the northern areas. Valley highs expected to be in the upper 70s to 80s.