Dry weather with a warm temperatures early this week. Cooler temperatures beginning midweek with a chance of precipitation next weekend.
Weak trough will pass through NorCal today with little impacts. Heights remain high despite the weak trough moving through and temperatures will be quite warm with Valley highs in the mid to upper 90’s. These readings are about 10 degrees above normal for this time year. 700 mb winds will remain less than 10 mph limiting mountain and ridgetop winds through Wednesday.
Trough will flatten as it moves east towards the Great Basin Tuesday with a more weak zonal flow pattern replacing it over NorCal. This will allow temperatures to rise a couple of degrees with Valley highs from the upper 90’s to low 100’s. Have opted to use the NBM 90 percent guidance, as operational NBM has been running about 5 degrees to cool over the past few days.
Trough will gradually deepen over the Pacific Northwest Wednesday and Thursday with lower heights and onshore flow developing over Northern California. This will bring a cooling trend with Valley highs cooling back into the low to mid 90’s Wednesday and then 80’s on Thursday. There will also be a gradual increase in mountain and ridgetop winds progressing towards the weekend.
Extended Discussion (Friday through Monday)
Upper ridging weakens Friday as deepening upper trough upstream and associated Pacific frontal system approaches. Baroclinic zone weakens over the weekend as it moves into northern portions of CA.
Deterministic models and ensembles differ with depth and progression of this wave with some precip possible mainly north of I-80. Drier NWly flow aloft expected on Monday. Below normal high temperatures expected through the extended forecast period.