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Widespread sprinkles, or light showers, possible today. Mainly late day thunderstorm chances expected over the Sierra Nevada through the week. Cooler temperatures persist today before warming to above average again by mid-week.
Monsoon moisture covers the region early this morning with TPW around 1 to 1.25 inches. The deepening moisture, but lack of strong lift or much elevated instability, is resulting in scattered light showers across the northern Sierra and southern Cascade Range with a few sprinkles at the lower elevations. Still doesn’t appear like there will be much chance for thunder early this morning.
The Delta Breeze has fizzled out for the most part as the marine layer becomes more shallow (down to around 1k ft deep at Fort Ord) and surface pressure gradients have balanced out. Current temperatures are mostly a bit cooler compared to 24 hours ago, but areas influenced by the Delta Breeze are actually running about 2-5 degrees milder compared to early Monday.
The remnants of the inverted trough will lift north across the area today. This feature is really stretched out and likely won’t provide too much lift. Best chance of showers today will be across the northern half of the forecast area with thunder chances expected mainly to the north and east with better instability later this afternoon. Temperatures will continue to be affected by the cloud cover with many inland areas expected to be around 10 degrees cooler compared to Monday. The waning Delta Breeze, and increased sunshine in the afternoon, will likely result in warmer temperatures today across the Delta, southern Sacramento Valley and northern San Joaquin Valley.
The upper level ridge will build back into the area Wednesday into the end of the week which will bring a warming trend to the region and we will see highs push back into the triple digits across the Valley. Milder overnight lows will also contribute to a return of moderate heat risk by Thursday. Diurnal thunderstorm chances will continue each day across the northern Sierra.
Extended Discussion (Saturday through Tuesday)
Upper high becomes reestablished over the 4-Corners region early next week as Eastern Pacific trough deepens, bringing southwesterly flow to interior NorCal. This should bring above normal temperatures that gradually cool towards the end of the period. Forecast highs in the Valley will be in the 90s. Monsoonal moisture surge could cause a few thunderstorms to develop along the Sierra crest over the weekend, mainly south of I-80.