Near to slightly below normal high temperatures expected through Saturday, then above normal Sunday into early next week. Isolated thunderstorms possible over the mountains Friday into the weekend. Best potential for thunderstorms will be over the weekend, especially over the Sierra and southern Cascades.
Discussion
Heights/thicknesses forecast to trend down today into midweek as upper troughing increases over interior NorCal. Marine layer depth has risen per Fort Ord profiler and flow through the Carquinez Strait has strengthened significantly overnight. As a result, low level CAA working its way through the Delta into the S Sac Valley this morning. 24hr temp changes showing KSUU running 11 degrees cooler with 4 to 7 degrees of cooling around the greater Sacramento area at this time. 850 mb temps drop into the lower 20s Deg C today, which taken dry adiabatically to the surface equates to 90s across the Sac/N San Joaquin Valleys this afternoon. Flow through the Carquinez Strait looks remain moderately strong today, which will result in additional cooling in Delta breeze influenced areas.
Short wave trough progged to move into the Pac NW Wednesday which will help to further lower heights over CWA and deepen marine layer. Potential for some morning stratus development into the S Sac Valley although any development near sunrise should be short lived. AMS continues to synoptically cool Wednesday with highs in the Central Valley forecast in the low to mid 90s, with 80s in Delta breeze influenced areas.
Below normal high temperatures expected to continue through the remainder of the week. Post tropical Eugene and associated residual mid-level moisture modeled to move into southern portions of the CWA towards the end of the week. Elevated instability progs showing potential for isolated high based thunderstorms over portions of our Northern Sierra Nevada zone Friday afternoon/evening.
Extended Discussion (Saturday through Tuesday)
Cluster analysis indicates that troughing over California will persist into the weekend, as the remnants of T.S. Eugene continue to influence the upper level pattern. Despite this, temperatures will look to warm to near normal on Saturday and back up above normal from Sunday into early next week. This will be the result of generally increasing heights aloft as ridging over the south central US begins to build westward once again moving into early next week. Rather, the primary impacts of the troughing over the region will be periodic chances for thunderstorm development across the weekend.
Persistent southwesterly onshore flow is expected to advect mid-level moisture across portions of interior NorCal on Saturday and Sunday. With enhanced lift from the approaching remnants of T.S. Eugene, there will be a slight chance (15-25%) for thunderstorm activity generally along and east of the Sierra crest and throughout the northern Sacramento Valley on Saturday and Sunday.
Moving into early next week, there is good ensemble consensus that ridging aloft will become the primary feature over the region. This will lead to another bout of warm, above normal temperatures throughout interior NorCal.
While there is still some spread regarding the exact degree of heating, there is increasing confidence in seeing widespread triple digits Monday and Tuesday throughout the Valley. Probabilities of exceeding 100F are generally in the 60-90% range Monday and Tuesday for Valley locations, with highest chances across the northern Sacramento Valley.