March 1, 2020 – A weather system continues to bring mountain and foothill snow, gusty winds, and cooler temperatures today. Sierra travel will be impacted through this morning due to periods of moderate snowfall. Strong northerly Valley winds today. Dry and warmer early next week with breezy north to easterly winds continuing.
Discussion
Moderate snowfall continues to fall over the Sierra this morning, impacting travel over Sierra passes. Upslope flow has created a near stationary band of precipitation right over the I-80 corridor east of Blue Canyon. Current Caltrans webcams show a few inches of snow covering I-80, and chain controls are in effect over many Sierra passes. Snow level radar near Colfax shows snow levels hovering between 4000-5000 feet over the past few hours. A positively-tilted trough is slowly moving through Northern California with the axis currently just north of the forecast area. Snow levels are expected to drop to around 2000-3000 feet by daybreak as the trough axis moves through. However, snowfall will decrease and become more showery by sunrise through midday, so only a light accumulation is expected with these lower snow levels. The Winter Weather Advisory remains through noon, though snow showers are likely to continue south of I-80 through the afternoon. An additional 2-5 inches of snow is expected today, most of which will fall early in the morning.
As the trough deepens and moves south today, winds will increase over the forecast area. Surface pressure gradients will tighten this afternoon and evening with models continuing to suggest a MFR-SAC gradient around 10-12 mb. North winds will be strongest in the northern and central Sacramento Valley, sustained 20 to 35 mph with gusts up to 40 to 50 mph possible. A Wind Advisory remains in effect from 10 am through 8 pm today. Although the strongest winds will decrease tonight, gusty north winds will continue through Tuesday as the upper trough closes over Southern California Monday and slowly moves southeast. One aspect to note is that minimum RH values will be very low in the Valley along with these winds. Fuels are becoming drier because of the lack of Valley rain in the past month, but they are not at at critical levels yet. Although we are not expecting enhanced fire weather concerns with this pattern, the combination of gusty winds and low RH could result in easier fire spreads if any fires were to start.
Upper level ridging builds again over California Tuesday and Wednesday, bringing dry weather and the return of above normal temperatures. Temperatures will be cool today before warming quickly Monday into midweek. Valley temperatures will once again be in the low 70s Monday and mid to upper 70s for Tuesday and Wednesday.
Extended discussion (Thursday through Sunday)
Tranquil weather expected thru Thursday as a transient upper ridge moves through resulting in high temperatures running around 8 to 12 degrees above average accompanied by abundant sunshine. By Friday and heading into next weekend, ensemble solutions continue to indicate the approach of a longwave trough. Probabilities have continued to trend toward a better chance for precipitation by as early as Friday and into the weekend. Snow levels should fall throughout the passage of the trough, reaching 2-3k feet by Sunday. It is too early to highlight actual precipitation amounts, but expect a shift in the pattern accompanied by cooling temperatures.
