April 21, 2020 – A few lingering showers possible over the northern Sierra Nevada this afternoon, otherwise dry through the remainder of the week except a chance of showers again across the northern mountains on Wednesday. Warming trend begins today with breezy northerly wind expected Thursday and Friday.
Discussion
Clear to partly cloudy skies cover the region early this morning. Winds are generally light, and temperatures range from the upper 20s and lower 30s in the mountain valleys, to the upper 40s to mid 50s across the Central Valley.
High pressure begins to build into NorCal today and will result in around 5-10 degrees of warming compared to Monday. Enough moisture remains for a few showers to pop up across the northern Sierra late today as weak instability develops with daytime heating.
Ridging from the eastern Pacific builds across NorCal through the remainder of the week. This will result in gradually warmer temperatures. By Friday, highs across the area are forecast to be around 10-15 degrees above average with warmest readings in the Central Valley approaching 90 degrees.
Dry weather is expected for most of the area through the remainder of the week, but a slug of deeper moisture (presently west of 40N/140W) will move over the ridge into far northern California and may lead to some light warm-advection precipitation across the northern mountains on Wednesday.
Extended Discussion (Saturday through Tuesday)
Dry weather expected through the extended forecast period. EPAC upper ridging flattens some over the weekend into Monday as several short wave troughs track through the PacNW. Result will be minor cooling, but daytime temperatures remain upwards of 10 to 15 degrees above normal. High temperatures trend up several degrees on Tuesday as upper ridging strengthens.