August 29, 2023 at 9:10 AM The National Weather Service in Sacramento has issued a Red Flag Warning for gusty winds and low humidity, which is in effect from 11 PM this evening to 8 PM PDT Wednesday. The Fire Weather Watch is no longer in effect.
Dry and seasonably warm weather prevails through mid-week. Increasing breezy to gusty northerly winds tonight and Wednesday may result in critical fire weather conditions. A cooling trend with some showers and isolated thunderstorms possible Friday into the weekend.
Discussion
GOES-West reveals clear skies across interior NorCal early this morning. Current temperatures are mainly in the mid 60s to low 70s across the Valley. HRRR smoke suggest some possible wildfiresmoke intrusion into portions of the northern Sacramento Valley this morning.
Expect Valley temperatures in the low to mid 90s this afternoon, with 80s to low 90s in the foothills, and 70s to mid 80s in the mountains. Slightly warmer temperatures are expected on Wednesday as Valley locations approach the century mark, with some areas of Moderate HeatRisk across portions of the southern Sacramento Valley and Delta. Ensembles and clusters show the trough tracking through northern CA today and moving into the northern Rockies on Wednesday. This will enhance offshore surface pressure gradients, resulting in breezy northerly winds tonight into Wednesday.
The Extreme Forecast Index (EFI) continues to highlight the elevated offshore winds. Peak wind gusts of 25 to 35 mph can be expected across the northern, central, and west side of the Sacramento Valley. Latest HREF and NBM guidance indicate a 20-50% probability of exceeding 40 mph along the west side of the Sacramento Valley tonight through Wednesday morning.
The low humidity values combined with breezy northerly winds could result in critical fire weather conditions along the western edge of the Sacramento Valley tonight through Wednesday.
A Fire Weather Watch remains in effect tonight through Wednesday. Avoid outdoor activities that can create sparks. The northerly winds may push wildfiresmoke into the Sacramento and northern San Joaquin valleys Wednesday morning per latest HRRR guidance.
Breezy winds are forecast to decrease Wednesday evening with an increase in onshore flow anticipated on Thursday.
Ensembles and clusters advertise an unseasonably strong upper low dropping south into NorCal late this week. This will lead to a significant cooling trend, with Valley highs cooling into the mid 70s to low 80s by Friday (10-25 degrees below seasonal normals).
There is also the potential for some showers and isolated thunderstorms for the Coastal Range, southern cascades, northern Sierra, and the northern/central Sacramento Valley on Friday. The EFI also depicts elevated onshore winds Thursday afternoon into Friday.
Extended Discussion (Saturday through Tuesday)
566 DM upper low located over the CWA Saturday will keep a threat of showers over interior NorCal. Decreasing threat of showers Sunday as upper low pushes into the Great Basin and upstream upper ridging builds inland. EC shows another deeper upper low moving across northern portions of CA late Monday into Tuesday. GFS, ensembles, and NBM support broader troughing aloft. Both suggest drier weather early next week.
High temperatues trend up through the extended period from upwards of 20 degrees below normal Saturday, to around 3 to 10 degrees below normal Tuesday.