April 19, 2019 – Chance of showers and thunderstorms across NorCal late today through Saturday. Snow levels generally above major pass levels. Cooler Saturday then fair skies and normal temperatures Sunday through mid week. Slight chance of showers northern mountains by the end of the week.
Fair skies over the forecast area this morning under upper level ridging over the western U.S. Temperatures are running a few to several degrees higher than 24 hours ago after a few to several degree climb in highs on Thursday. Upper ridge axis shifts eastward today as a weak trough drops out of the Gulf of Alaska. Increased onshore flow and slight airmass cooling will bring a little cooling today but daytime highs will remain well above normal. Models still paint some light precipitation over the coast range by 00z this afternoon spreading westward overnight. MU cape progs showing enough instability for a thunderstorm threat through the evening hours until daytime surface heating drops off. Main upper trough drops southeast through NorCal on Saturday. This will bring shower chances southward to about Sacramento with enough instability for return chances of thunderstorms. Cooler air associated with the trough will bring a significant drop in daytime temperatures with highs forecast at or a little below normal. Upper ridge begins building in late Saturday night with an end to any shower threat expected by Sunday morning.
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Fair skies and warming put daytime highs back to several degrees above normal by Sunday afternoon. More warming expected on Monday as the upper ridge builds along the west coast with daytime highs back to 10 to 15 degrees above normal.
Extended Discussion (Tuesday through Friday)
Not much change to the extended forecast this morning as model guidance continues to support high pressure building over the area. We`ll see another warm week with high temperatures featuring the 80s for the Valley while the ridges top in the 60s and 70s. The warmest days look to be Tuesday and Wednesday with temperatures then decreasing each day due to a broad upper level trough moving into the region. This will bring at at least an increase in cloud cover to northern California and perhaps even some isolated showers and thunderstorms.