Another cool and dry morning ahead a weather system bringing moderate to heavy rain and snow and gusty winds Wednesday night to Friday.
Discussion
Things will remain relatively quiet throughout the morning with most precipitation falling as virga and just across the far southwestern corner of the CWA. Precipitation moves into Interior Northern CA this evening over the western side of the Valley and track westward throughout the Thursday early morning.
Thursday morning will be the wettest period, first in the Valley then by late morning over the Sierra. Snow and rain rates begin to taper down Thursday night into Friday morning with most precipitation over by very early Saturday morning. Here is a look into impacts during this stretch of weather.
Beginning with snow, snow level Wednesday night will be 1500-2500 feet over Shasta County/Coast Range areas with 3000-4500 feet over the Sierra mountains. Increasing snow levels move in from the south and by Thursday morning be 3500-5000 feet over Northern Shasta and 5000-7000 feet across the Sierra. By the evening much of Northern CA will see 4500-5500 feet before lowering to around 4000-5000 feet Friday morning. This will bring periods of moderate to heavy snowfall with feet of snow expected for the Sierra above 4500 feet and up to a foot for the Northern Shasta County areas above 2000 feet.
Additionally, there continues to a chance of snow across the lower elevations of the Northern Sac. Valley with EC and GFS Ensembles showing snow accumulations as low as Redding although is a high level of uncertainty, combined by the potential mitigating effect of snow falling on rain and/or there being a mix of rain and snow. Local effects could really come into play and in areas where cold air can be trapped may see snow but locally warmer areas see rain or mixed precipitation. No matter what, plan for slippery road conditions and travel delays as the weather system moves through.
With all that being said, Winter Storm Warnings remain in effect for Northern Shasta County/Coast Range above 2000 feet from 10 PM Wednesday to 4 AM Friday for 3-8 inches with 1-2 feet above 3500 feet and winds up to 45 MPH. For the Sierra and Southern Cascades, our Warning will be from 10 PM Wednesday to 10 PM Friday for 2-5 feet possible above 6000 feet and 5-15 inches between 4500-6000 feet and winds as high as 60 MPH. Very difficult travel conditions with chain controls and road closures are expected and heaviest snowfall is expected on Thursday with rates of 1-2 inches per hours at times.
Widespread rain will impact interior NorCal over the same timeframe. The NBM shows a 60-90% probability of 1 inch of rain or more in the Valley with a 60-90% probability of 2 inches or more in the foothills. Rain may be moderate to heavy at times, creating slick roads, mud/rock slides in the foothills, high flows on area waterways and minor flooding issues.
There is also a 10 to 20 percent probability of isolated thunderstorms Thursday afternoon through Friday that could lead to locally heavier rain amounts. A Flood Watch has been issued for elevations below the primary snow line to address these conditions.
Gusty southerly winds are forecast with this system, generally around 30 to 50 mph gusts in the lower elevations Wednesday night through early Friday, strongest on Thursday. A Wind Advisory has been issued for portions of the Valley to address impacts such as difficult driving conditions for high profile vehicles, potential power outages, downed trees or tree branches, and loose objects blowing around.
Saturday looks to be mostly a transition day after the mid week storm tapers off and we see a brief break in precipitation. Saturday evening will see light showers move ocer the Northern Sac. Valley and Southern Cascades are with 25-55% of seeing precipitation.
Extended Discussion (Sunday through Wednesday)
Ensemble guidance then indicates by Sunday morning another weather system has pushed its wave into the Northern CA, mainly over the mountains and N. Sac. Valley. This system looks much weaker than the upcoming mid- week storm, and appears to be more progressive as well. Little to no impacts are expected from this weekend storm, with just some dusting of snow, light showers, and locally breezy winds.
On Monday, as any lingering precipitation tapers off, it appears we can expect a return to drier and slightly warmer weather that continues into Tuesday.