Active weather returns today and persists through the weekend into early next week. Periods of rain, mountain snow (heavy at times) and gusty wind are expected.
Discussion
Large blocking ridge continues to lift north toward Alaska allowing energy across the Pacific to reach NorCal. The first system is approaching early this morning with considerable clouds now covering the region. This will once again inhibit fog formation early this morning. Current temperatures are running around 4-8 degrees milder compared to 24 hours ago and are in the mid 40s to lower 50s in the Central Valley, and mainly in the 20s and 30s over the mountains.
The warm front is moving overhead early this morning and some light precipitation is beginning to show up on radar across the northern mountains and far north end of the Sacramento Valley. The warm front will lift north this morning with precipitation expected to begin increasing across northwest California as the cold front moves in, and then spread south and east reaching the Sacramento area and Sierra by later this afternoon and evening.
Southerly wind will also increase by later this morning as surface pressure gradient tightens with the approach of the front. Gusts up to 40 mph will be possible across the northern half of the Sacramento Valley this afternoon, and gusts of 50 mph or higher will be possible across exposed higher terrain areas. Wind will decrease this evening behind the cold front.
QPF hasn’t changed much through Thursday and is still around 0.50″ or less through most of the Central Valley (around an inch up by Redding), and 1.50″ to 3.50″ over the mountains. Rain with the cold front will likely develop around early afternoon up by Redding, and reach the Sacramento and Stockton area later in the afternoon or by the evening commute.
In the Sierra and south Cascades, the higher elevations may see some flurries or a dusting of snow this morning as the warm front lifts north (especially up by Mt Lassen), but the more impactful snow will develop this afternoon and continue overnight into early Thursday morning.
Snowfall rates of 1-2 inches per hour will be possible above 6k ft with 1-2 feet of accumulation expected over the higher passes by Thursday morning leading to major travel impacts.
A relative break is expected through most of Thursday and Friday as short-wave ridging transits the area.
The first wave of the weekend series looks to have slowed somewhat, and precipitation is more likely to arrive Saturday afternoon and evening. Snow levels are expected to be a little higher with significant accumulation mainly near the higher passes.
Extended Discussion (Sunday through Wednesday)
An active weather period continues through Wednesday as several waves of precipitation move through our area.
By Sunday, our pattern will be dominated by troughing and west-southwesterly flow. An upper-level low, coupled with moistureflow from the tropics in the Pacific will bring periods of moderate to heavy rainfall, high-elevation mountain snowfall, and gusty southerly winds throughout the extended period.
Widespread precipitation continues through Sunday morning, before a brief break ahead of another wave of precipitation beginning Sunday night. The National Blend of Models (NBM) is advertising a 50-90% probability of exceeding 1.00″ of rainfall in the Valley through Sunday, with the probabilities greater than 70% for the northern Sac Valley.
NBM snowfall probabilities of exceeding 8.00″ or more are 45-65% along the I-80 corridor. Snow levels are forecast to be 6000-7000 feet during the first wave of precipitation, lowering to 5000 to 6000 Sunday evening prior to the second wave. Gusty southerly winds of 30 mph or more in the Valley are forecast to accompany this first wave as well.
We’ll see a brief reprieve in precipitation before the second wave arrives Sunday evening, lasting through Wednesday.
This “break” will be characterized by light rain/mountain snow Sunday afternoon.
In regards to the second round of precipitation, the NBM has 50-80% probabilities of exceeding 1.00″ of rainfall over the Valley/Foothills with probabilities greater than 65% north of I-80.
Snowfall probabilities of 12.00″ inches or more are 60-80% along I-80 and US HWY-50. Snow levels are forecast to lower to around 5000-6000 feet Sunday night through Wednesday.
Gusty winds of 20 to 30 mph are expected as well for this second wave.
Make sure to check road conditions frequently and check the forecast often for updates, especially if you have holiday travel plans. Forecast uncertainty persists regarding timing and precipitation amounts, so keep up to date with the latest forecast by checking our social media and website.