February 23, 2019 – Wet weather returns to northern California this weekend and will continue into next week.
The forecast remains on track this morning as clouds continue to stream into the region. This cloud cover will primarily cover northern portions of the CWA which should inhibit frost from forming. Farther south, in the central Sacramento Valley and northern San Joaquin Valley, recovering dewpoints and clear skies could lead to some patchy frost development. As the day continues, cloud cover will continue to spread over the region and chances for precip will increase. Most of the rain and mountain snow will be confined north of the 50/80 corridor and primarily effect the northern portion of the Sacramento Valley. Snow levels will initially range from 2500 ft in the Shasta County mountains to near 4000 ft over the “Coastal Range”. Impact wise, travel along highway 299 may be difficult at times since several inches of snow will accumulate, especially as we head into tonight and Sunday. Precip continues into Sunday and will eventually spread over the southern half of the CWA as this system taps into a weak AR.
From Sunday nite into the middle of next week, precip will become become steadier and heavier over northern California. The West Coast AR Landfall Tool implies that this moisture plume (AR) will impact NorCal through the 27th (Wed). For the 80/50 corridor, precip is forecast to move into that area early Monday, and should become heavy over the Hwys 70/36 corridors by Monday afternoon. Winds will also be increasing Mon and Tue as the bulk of the AR moves inland. The WAA from the AR will raise snow levels to at least 5-6 kft, if not higher over the Sierra.
The timing of the weather systems, duration of the AR, and the relatively low snow levels initially, followed by rising snow levels during the event, warrants segmenting the WSW product. Not the easiest way to handle this, but the different areas will be impacted differently, both in time and quantity of precip. After snow levels rise above 5 kft, there is little impact for zones 13 and 63, while impacts continue for the Sierra. The runoff from the precip through the middle of next week will cause rivers to rise, so expect some hydro impacts as well.
Extended Discussion (Wednesday through Saturday)
The forecast remains on track, with an active weather pattern continuing to look likely for the extended portion of the forecast. QPF amounts on Wednesday suggest less than 1″ across the area. Hazardous mountain travel is anticipated, with snow levels around 5,500 to 6,500 feet. Forecast models disagree with how quickly to eject this system on Thursday, with the ECMWF being more progressive. Thus, lingering mountain showers could be possible on Thursday. Otherwise, dry conditions are expected for most areas as weak ridging develops between systems. A return of precipitation is likely late Friday into next weekend as the next system approaches from the west bringing widespread precipitation.