Discussion
Early morning GOES-West satellite imagery and RADAR illustrate scattered showers over portions of interior NorCal with snow showers up in the mountains. Latest weather observations are indicating cooler temperatures across the area, around 2 to 10 degrees difference from 24 hours ago, valid at 230 AM PST. The Winter Weather Advisory remains in effect through 4 PM PST this afternoon to address any additional travel impacts associated with the mountain snow showers above 3000 to 4000 feet. Additional precipitation amounts of a few hundredths in the Valley up to a quarter inch in portions of the foothills are forecast today. There is a 30 to 70 percent probability of additional snow amounts of 4 inches or greater in the mountains today as well.
Low temperatures Thursday night will be on the colder side, in the 30s in the Valley, 20s to 30s in the foothills, and teens to 20s in the mountains. Dry and warmer daytime weather returns Friday and through the weekend. Valley high temperatures start off in the mid 60s on Friday and increase to the upper 60s to low 70s by Sunday under upper level ridging. Northerly flow will develop on Friday behind the passage of the current weather system, and some gusts of around 15 to 20 mph will be possible at times in the Valley, with gusts up to 20 to 30 mph in the mountains. Tranquil weather is overall in store Friday through Sunday, before active weather makes a return for next week.
Extended Discussion (Monday through Thursday)
Ensemble guidance and cluster analysis show high confidence in an active weather pattern returning to the forecast over the extended forecast period with multiple weather systems moving through Monday and again Tuesday through Thursday bringing along rain, wind and mountain snow impacts to interior northern California.
Here is a look at some 72 hour probabilities from the National Blend of Models (NBM) ending 5 AM Thursday:
Probability of Rain > 1 inch: 55-95%
Probability of Rain > 2 inches: 15-30% (Valley), 50-80% (foothills)
Probability of Mountain Snow > 36 inches: 55-95%
Probability of Mountain Snow > 48 inches: 50-90%
Probability of Wind Gusts > 50 mph: 30-70% (Valley/foothills)
Probability of Wind Gusts > 65 mph: 45-75% (mountains)
In addition to the higher probabilities from the NBM, the Extreme Forecast Index (EFI) is also highlighting the potential for these impacts, especially in the middle of next week.
Although there is still some uncertainty in exact details such as snow levels, precipitation amounts and wind speeds, confidence is high in the active weather over the extended forecast period for Interior NorCal. Stay tuned for more information as we get closer and plan ahead for wet, cool and windy weather!