April 15, 2021 – A few late day showers will be possible over the northern Sierra south of Lake Tahoe on Friday and Saturday, otherwise dry and warmer weather expected into next week.
The low is a bit further east early this morning and skies have cleared out across NorCal following Wednesday afternoon’s deep convection over the mountains. Surface pressure gradients have continued to relax and winds are generally light. Current temperatures range from the mid 20s in the colder mountains valleys, to the upper 40s to mid 50s across the Central Valley.
The closed low shifts east into the Rockies today allowing heights aloft/thickness to recover a bit leading to modest warming for most areas. CAMS indicate that there won’t be sufficient surface heating today to generate enough instability for deep convection over the mountains.
Further warming is expected Friday and Saturday, and enough late-day instability may be present for some isolated shower development over the mountains given the lingering “hang back” trough beneath the large blocking high over southern BC.
The warmest days coming up appear to be early next week as the ridge moves overhead beginning Sunday when highs in the upper 80s to lower 90s are forecast across the Central Valley.
Extended discussion (Monday through Thursday)
Upper ridging over the area Monday weakens as short wave trough rides the ridge into NorCal Tuesday. Models diverge significantly with strength and position of this feature leading to forecast uncertainties.
Ensembles support slight chance of some light associated precip Tuesday over Shasta and Western Plumas counties. Short wave trough digs into the Great Basin Wednesday as secondary wave drops through eastern portions of the CWA.
Threat of showers shifts to the Sierra Nevada on Wednesday. Dry weather expected Thursday as EPAC upper ridging rebuilds inland.
High temperatures progged 10 to 20 degrees above normal through the extended forecast period.