Cool temperatures persist through the end of the week, with a slight warming trend across the weekend and into next week. Gusty north to east winds and drying conditions are also anticipated Saturday into Sunday. Dry and quieter weather is then expected early next week.
Discussion
As of early this afternoon, some lingering stratus persists over portions of the northern San Joaquin Valley, with otherwise clear skies elsewhere within interior NorCal. Despite this, temperatures across the region remain in the low 60s within the Valley and 40s to 50s at higher elevations.
With breezy northerly winds across the region prevailing this afternoon, high temperatures are only expected to warm into the mid to upper 60s across the Valley and 50s to low 60s at higher elevations. Moving into the overnight period, mostly clear skies and calming winds will aid in temperatures dropping into the mid 30s to low 40s in the Valley, with coolest temperatures expected at Valley floor locations.
As a result, some isolated instances of frost may be possible overnight into Friday morning. Large scale troughing will continue to dominate the flow pattern aloft through the end of the week and into the weekend.
Another shortwave is progged to travel through this pattern over the weekend period, but prior to this, generally quiet, dry, and cool weather is anticipated on Friday ahead of the system. As the aforementioned shortwave tracks east-southeast into the Great Basin region Saturday into Sunday, gusty north to east winds will accompany it.
At this time, winds are generally expected to increase around midday Saturday, peak during the evening and overnight hours into Sunday morning, then taper off by late day Sunday. Sustained winds of 15 to 25 mph are anticipated, with gusts up to 30 to 40 mph for Valley locations. Some areas within the mountains may see gusts to 50 mph as well.
Latest NBM probabilities indicate a 30-50% chance for portions of the Sierra to see wind gusts to 50 mph, with a 10-40% chance to see gusts to 40 mph along portions of the western Sacramento Valley. It should be noted that probabilities for gusts to 40 mph are in the 50-70% range for the Delta area as well.
Relative humidity values are also expected to fall as the dry north to east winds prevail. Afternoon minimum relative humidities plummet into the low teens to low 20s for most locations on Saturday and Sunday. Additionally, overnight relative humidity recovery will be limited to the 20 to 40 percent range for locations below 3000 feet elevation. These factors combined will result in at least elevated fire weather conditions for much of the forecast area across the weekend.
Otherwise, as this shortwave is generally expected to track inland, precipitation chances are decidedly low (less than 5%). Temperatures will begin a slight warming trend through the weekend as well, with highs in the low 70s returning to Valley locations by Sunday afternoon.
Extended Discussion (Monday through Thursday)
After the weekend and into early next week, cluster analysis of the ensembles suggest fair agreement with the placement of a ridge axis offshore the West Coast. This would result in dry, northwesterly flow for much of the Golden State early next week, along with a slight uptick in temperatures compared to the weekend.
Forecast uncertainty begins to increase by the middle of next week with respect to the timing of the ridge flattening or breaking-down over the Pacific Northwest. The Euro ensemble keeps the region generally dry through next week while a decent number of the GEFS members bring light precipitation for the northern third of California around Thursday.
The National Blend of Models (NBM) takes into account all possibilities and compromises with a 15-25% probability of precipitation from around Butte County and points north and < 15% for points south.