Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
309 FXUS66 KSTO 270944 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 244 AM PDT Fri Sep 27 2024 .Synopsis... A strong warming trend begins today, with well above normal temperatures continuing into next week, peaking early in the week, with widespread triple digit highs in the Delta and Valley possible by Tuesday. Northerly winds and low humidity could bring elevated fire conditions early next week. && .Discussion... The area is currently between a weak low off the coast and ridging centered over the Four Corners region. This ridging is expanding westward into the area with increasing heights over interior NorCal. The marine layer is much shallower (~500 feet) than yesterday, being compressed by the ridging and onshore flow is much weaker this morning. This will result in less onshore cooling, lower humidity and a lack of marine stratus clouds spreading in through the Delta, unlike early yesterday. High temperatures this afternoon will be much warmer, 6-12 degrees above normal for this time of year. For the Valley and Delta this will mean mid 90s to 100. Humidity will drop into the teens to low 20s. Winds will be light and variable today, limiting fire concerns for the time being. The low off the coast will phase with Pacific Northwest troughing bringing a return to light onshore flow, a little higher humidity and slightly less hot temperatures, especially for Delta breeze influenced areas. Highs will still be around 5-10 degrees warmer than normal, though. Sunday evening and overnight hours, the low will move into Southern California. Eastern Pacific ridging extends over the area, with the 4 Corners ridging extending westward. This will bring hot temperatures and widespread Moderate HeatRisk. Drying northerly winds will develop Sunday night through Monday, with gusts to 20-25 mph by mid-day. Afternoon humidity will drop into the 10-20% range for much of the area. The winds and low humidity will combine to bring elevated fire weather concerns to our area, especially over the northern and western Sacramento Valley, and into the foothills. && .EXTENDED DISCUSSION (Tuesday THROUGH Friday)... Strong high pressure in EPAC extends inland over NorCal early next week resulting in well above normal temperatures with moderate to locally major heat risk. Areas of gusty north to east wind combined with low humidity continue elevated fire weather conditions in the Sacramento Valley and adjacent foothills early Tuesday. Upper ridging weakens through the second half of the week as short wave trough progresses through the PacNW. Models differ with how deep the troughing extends south, and clusters showing large variability. NBM leans towards GFS with deeper upper troughing extending into NorCal, while EC maintains more ridging aloft. For now, forecast leans towards NBM solution with cooling trend Wednesday into Friday with increased onshore flow and higher humidity. NBM advertising near normal high temperatures Thursday, then below normal Friday. && .AVIATION... VFR conditions over interior NorCal next 24 hrs with sfc wind below 12 kts. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$