A quick moving system brings additional precipitation impacts to interior NorCal today into early Tuesday, followed be drier weather through mid to late week. A shift back toward more active weather may be possible by next weekend, but details remain quite uncertain at this time.
Discussion
Misty-like conditions are present in the Sacramento area, lowering visibilities at a few airports. Further north into Shasta County along the Coastal Range, areas of mountain snow and rain showers have moved onshore. Some early 6-hour precipitation totals around Shasta County have anywhere from a trace to roughly 0.10″ of an inch so far. Precipitation is expected to continue through today and into early Tuesday.
A trough associated with an area of low pressure located in the PacNW is responsible for the current precipitation in the area, and the trough will continue to move through the region as we move through the day. Most of the precipitation impacts will be in the northern Sacramento Valley and mountains of Shasta County/Lassen NF, however some precipitation is anticipated to make it further south into the rest of the Valley and in the Sierra and Southern Cascades and adjacent foothills. Overall snowfall totals for the Shasta County mountains and Coastal Range looks to remain on track at around 5-12 inches with locally higher amounts on peaks through Tuesday AM. NBM probabilities remain at around 60-90% for 6 inches of snowfall or more through Tuesday. For locations in the Sierra and Southern Cascades, 3-8 inches is expected, with the higher totals forecast north of I-80 and specifically at Lassen NF. NBM probabilities of 4 inches or more of snowfall are around 20-60%, with higher 80-90% probabilities at Lassen NF. As a result of the projected snowfall totals,
A Winter Weather Advisory is in effect now for the Shasta Mountains and Coastal Range until 4 AM Tuesday for elevations at 3000 feet and above. The Sierra Winter Weather Advisory will go into effect at 4 AM this morning through 4 AM Tuesday for elevations above 5000 feet. If you are traveling or have to drive through areas in either Advisory, be sure to check road conditions before heading out, as travel delays and chain controls will be possible.
Not much change in overall forecast rainfall totals for the Valley from this system, with anywhere from 0.10″ in Modesto up to around 0.50″ forecast for Redding. With the current track of this system, most of the impacts will be felt in Shasta County, and the foothills of the Sierra in terms of rainfall. As the system vacates the area Tuesday, winds will shift from the north, however PGF will not be as strong as last weekend, therefore wind gusts will generally be below 15 mph except in the higher elevations of the Sierra Nevada.
As the system exits, upper level ridging is forecast to develop and help clear and dry things out through the end of the week. High temperatures will climb to slightly above normal starting Tuesday with highs in the upper 50s to low 60s for the Valley and lower elevations of the foothills. Higher elevations will be in the upper 40s to mid 50s from Tuesday through Thursday.
Extended Discussion (Friday through Monday)
Ensemble guidance continues to suggest a potential shift to more active weather towards the weekend, however many solutions regarding the track and potential precipitation impacts exist. Cluster Analysis reveals there is potential for the upper ridging to hold in the area Friday, or a making its way into the region. If the ridge holds Friday, we may see a delay of the onset of precipitation until late Friday night/early Saturday morning.
Current NBM QPF guidance is suggesting that once again, the bulk of the impacts would be along the northern Sacramento Valley and the Foothills of the Sierra Nevada/Southern Cascades. Early look at the snow levels also suggests this system may be warmer than our previous storms, with snow levels at and above 7000 feet. With the uncertainty regarding track, location, and strength, continue to check back for updates as we move through the work week and the details will start to iron out.