September 29, 2018 – A weak storm system will brush part of the region mainly late today and tonight along the coastal range. Light amounts of precipitation are expected into Sunday morning before ending.
Another storm system approaching the coast on Monday will bring a better shot of widespread rainfall Monday night and Tuesday.
Discussion
Low pressure area off the coast will move northeast today and tonight. This will increase precipitation chances mainly along the coastal range and over western Shasta County and the Delta fire late today and tonight. The low has stretched the marine layer which may translate into low clouds spreading into the valley later this morning. Winds will be breezy for some valley areas today to locally windy over mountain peaks. T
emperatures will be cooler today only warming into the mid 70s for many areas in the valley. Mountains will generally warm up into the upper 50s and 60s today. Have left in slight chances of thunderstorms over the Delta fire but greatest instability continues to be further north and northwest of Shasta County. Some residual showers may persist on Sunday morning over the north as the low moves northeast away from the region. There will be a break from threat of showers most of Sunday and Monday before another low pressure system impacts the region.
Currently the timing looks like it would be mainly Monday night and Tuesday for when the low moves past the region and the best shot of precipitation. Precipitation totals remain uncertain at this time with the low tracking southward off the coast and into Southern California. Latest NAM run has backed off on the precipitation amounts inland but it still indicates some decent amounts along the coast.
Extended Discussion (Wednesday through Saturday)
We will see an unsettled weather pattern to start out the extended period with a decent amount of uncertainty do to model differences. An upper level low will be set up over SoCal on Wednesday but the EC is a bit slower with this keeping it off shore. This will allow for some weak instability to build into the area along with some forcing, keeping rain chances in the forecast. The GFS is a bit quicker with this and keeps things drier. Did keep rain chances in the forecast for Wednesday with the best chances in southern parts of the CWA.
Another short wave trough will drop down and track over the region late Wednesday and Thursday. Once again we see some model differences with the GFS quicker and weaker with this.
Either way rain chances look to continue into Thursday but should be limited to the higher elevation with the valley staying dry. Upper ridging builds into the forecast area on Friday with drying and warming conditions. Locally gusty northerly wind develops over portions of Interior NorCal on Friday and Saturday. Below normal high temperatures expected through Thursday warming to slightly above normal Friday and over the weekend.