Dry weather with morning fog expected today. First storm in a series of systems will move into area Saturday followed by more systems into mid week next week including Christmas.
Discussion
Areas of dense fog have developed around the Sacramento Valley once again this morning. Lowest visibilities are being observed in the northern Sacramento Valley, with Redding AP at 1/4 mile and Red Bluff AP at 1/2 mile. Low visibilities due to fog are expected to continue this morning, and a Dense Fog Advisory is in effect for the Sacramento and northern San Joaquin Valley until 11 AM this morning. If you encounter areas of dense fog on the morning commute, slow down, leave plenty of space between you and the car in front of you, and use your low-beam headlights.
Outside of the morning fog, today will be the last dry and quiet weather day for the area, as a series of storms is expected to move into the area beginning tomorrow morning. An area of low pressure in the PacNW will eject a relatively warm trough with precipitation chances across the area.
The better moisture with this system still looks to remain mostly north of our area, however the northern Sacramento Valley, southern Cascades, and the Sierra and adjacent foothills will see the heaviest of precipitation. Latest rain totals from this first wave have remained unchanged from yesterday’s forecast. Aforementioned locations stand to receive around 0.75 to 1.25 inches of rainfall through early Sunday morning. Snow levels continue to remain above 6000 feet for the Sierra, and around 5500 feet for the mountains of NW Shasta County. Total snow accumulations look to remain around a dusting to 2 inches, with locally higher amounts on peaks and specifically at Lassen NF/NP.
Late Saturday night into early Sunday morning, a brief break from widespread rain/showers and high elevation snow is expected. Another wave of precipitation then enters the area Sunday morning, with similar impacts and snow levels above 8000 feet, as warm southerly air continues to flow into the area. NBM probabilities remain at around 15-30% for locations in the central/southern Sacramento Valley, Delta, and northern San Joaquin Valleys, while a 65-90% chance for 0.50 inches in the northern Sacramento Valley, mountains and foothills through Monday morning. Overall, mountain travel this weekend does not look to be majorly impacted, with primarily wet roads as the potential travel concern. Another brief reprieve from widespread precipitation is expected Monday afternoon, then a third, wetter, and cooler system is expected to move in.
The third system is expected to bring precipitation chances Monday afternoon through early Christmas Day. Of the three systems in the short term forecast window, this system will have better moisture support for the entire region. While the higher precipitation totals will still be in the northern Sacramento Valley, mountains of Shasta County, southern Cascades, Lassen NF/NP, and the Sierra and adjacent foothills.
NBM probabilities of at least an inch of rainfall through early Christmas morning are around 70-100% for the above mentioned areas, while the rest of the Valley, mainly from Redding southward 40-70% chance of an inch. Cooler air is anticipated to rush in behind this system, so snow levels will fall as the main wave makes landfall and pushes inland. Snow levels begin at around 8000 feet Monday night/Tuesday morning, then fall to around 5000-6000 feet Tuesday night.
While the bulk of the precipitation will have moved out of the area as the coldest air arrives, accumulations of snow could impact Christmas Eve travel during the nighttime at around 6000 feet and higher. NBM probabilities of around 6 inches of snow at elevations 6000 feet and higher are around 30-50%, so we are not anticipating major impacts to travel at this time, however an Advisory may be needed to cover higher snowfall rates and accumulations.
Breezy southerly winds will also accompany this third system, with strongest winds in the Valley from Yuba City to Redding and in the mountains and foothills of the Sierra. If you have travel plans this weekend through Christmas, please check road conditions before heading out, and keep checking the forecast for changes.
Extended Discussion (Tuesday through Friday)
As mentioned in the short-term forecast discussion, the third system will continue into early Christmas Day, then another break in precipitation is likely until later Christmas night. Ensembles depict another trough ejecting into the area, slightly further south and eastward than previous troughs. With the current EC ensemble guidance track, this system will be cooler and could bring widespread precipitation to the region all day Thursday and into Friday morning. Early forecast precipitation totals may be running too hot, as probabilities of snow in the mountains are around 30-60% for 6 inches of snow at around 5500-6000 feet and higher, but the totals forecast are around 6-13 inches.
Heavier rain totals look to once again be in the northern Sacramento Valley, southern Cascades, Lassen NF/NP, and the Sierra and adjacent foothills, but again the probabilities the NBM are showing are skewed from the forecast rain totals. There is much uncertainty with this system, as clusters have to resolve a definitive solution to track and strength. Stay tuned to the forecast for updates as we move through the weekend when ensembles and cluster analysis come into better agreement.