Breezy northerly winds, dry conditions, and near normal temperatures are anticipated today. Increasing precipitation chances are then expected from Friday into the weekend. Quieter weather and a slight warming trend are then in store early to mid next week.
Discussion
Early this morning, quiet weather is being observed over interior NorCal. Resultant temperatures throughout the valley are in the 50s to 60s, with 40s to 50s across the foothills and mountains at this time. Latest satellite imagery shows nary a cloud in the sky over the forecast area as well.
After a cool start to the morning, look for high temperatures to rebound back to near normal values by the afternoon. Northerly winds do look to increase throughout the day as well, but remain generally light, with only occasional gusts over 20 mph for portions of the northern Sacramento Valley expected.
Moving toward the end of the week and into the weekend, a shift in the overall pattern looks to take place. Upper level troughing currently positioned over the Pacific Northwest is expected to dig southward and deepen over interior NorCal. This will result in temperatures cooling to well below normal over the weekend, as well as precipitation chances increasing across the forecast area.
The timing and location of the trough will have a large bearing on the overall timing and location of attendant precipitation impacts. Highest probabilities for appreciable precipitation are anticipated across the mountains, with lower, but still nonzero chances throughout the foothills and adjacent portions of the Valley.
Latest NBM guidance indicates a 30-50% chance of precipitation exceeding 0.5″ over the mountains, with a 20-40% chance of precipitation exceeding 0.25″ across the Valley and foothills. Despite the overall cooling trend expected with this system, some weak instability may be present on Saturday, which may lead to some isolated thunderstorm activity as well. Any thunderstorms that do develop would have the potential for occasional lightning, brief heavy rainfall and gusty erratic winds.
Precipitation chances begin to taper off on Sunday, with only slight (15-25%) chances remaining possible over the Sierra.
Extended Discussion (Monday through Thursday)
By early next week, the upper trough is generally expected to have pushed eastward toward the Four Corners region. This will leave interior NorCal underneath dry northerly flow on the back side of this system. As a result, cool temperatures and dry weather are anticipated on Monday.
Cluster analysis continues to favor ridging building in behind the weekend trough that is set to impact the region. This will lead to persistent quiet and drying weather throughout the majority of the long term period. Resultant temperatures look to creep upwards to near to slightly above normal values for early October across mid to late week.