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Widespread precip and breezy winds today into Thursday morning. Low elevation snow will be possible in the northern Sacramento Valley and adjacent foothills with this system. Cold nights Friday and Saturday night. Rain and snow chances return for the second half of the weekend with unsettled weather next week. Winter Storm Warning from 10 AM this morning to 10 AM PST Thursday for Motherlode-Northeast Foothills/Sacramento Valley- West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.
Water vapor is showing our next trough about 250 miles off of the CA/OR boarder at this time. Some light precip is showing up on radar over northern portions of the region in an area of weak warm air advection. Not much of this is making it to the ground as we have some dry air in the mid-levels.
Profiles will continue to saturate this morning and low level warm air advection will really amp up late morning into the afternoon as an 850 mb jet intensives to 50+ knots ahead of an approaching cold front. This will bring widespread showers to the area with moderate to heavy mountain snow.
The cold front with this system should reach northern areas by the mid afternoon and continue to push south during the evening and overnight. Activity will continue behind the cold front though as the trough axis pushes through.
Shower activity will diminish Thursday morning into the early afternoon as the trough axis pushes to the east. Cold air is in place and we are seeing low snow levels this morning with them as low as 500 feet over Shasta County and 1000 feet over the Sierra. Currently Redding’s wet bulb temp is 35 and that would support some wet snow. We will have to keep an eye on that as precip pushes in this morning, right now it’s looking like some light snow in Redding this morning before switching to mainly rain by the late morning. Snow accumulation for Redding is expected to remain under 1″ but there is still some uncertainty with that even at this hour.
The warm air advection with this system will bring higher snow levels but it’s uncertain how quick we will see them rise during the morning and afternoon but we should see them reach 1000 to 2000 feet over Shasta County and 2000 to 3000 feet over the Sierra during the afternoon.
We do see some weak CAPE above the saturated inversion ahead of the cold front and some mid-level CAPE behind the front in the trough axis. CAPE looks very limited and not enough to put thunder in the forecast though. QPF with this system is looking to be 0.40 to 1.10″ over the valley, 0.75 to 2″ over the foothills and 1.75 to 3.5″ over the mountains.
Now the majority of this will be snow above 2500 to 3000 feet. Generally 1 to 3 feet of snow above 3000 feet with some light accumulation down to 500 to 1000 feet in the Shasta County and down to 2000 feet in the Sierra.
With the strong low level jet wind will be another component with this storm system. We will see gusty winds this afternoon into the overnight with valley gusts up to 40 mph, locally higher and up to 60 mph in the mountains. These winds along with the snow will bring whiteout conditions for the mountains and travel will be difficult to impossible.
Extended Discussion (Sunday through Wednesday)
Upper level ridging will be pushing east at the start of the extended period. We will see a weakening trough push into the PacNW Sunday pushing a cold front into our area. This will bring some shower chances Sunday.
Ensembles then support long wave troughing developing over the west early next week bringing an extended period of unsettled weather. Ensembles are in great agreement on the long wave troughing but do differ some on its placement and timing of exact waves of precip. Multiple rain and snow chances are likely but details on timing aren’t great at the moment.